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The kprobes and synth event generation test modules add events and lock
(get a reference) those event file reference in module init function,
and unlock and delete it in module exit function. This is because those
are designed for playing as modules.
If we make those modules as built-in, those events are left locked in the
kernel, and never be removed. This causes kprobe event self-test failure
as below.
[ 97.349708] ------------[ cut here ]------------
[ 97.353453] WARNING: CPU: 3 PID: 1 at kernel/trace/trace_kprobe.c:2133 kprobe_trace_self_tests_init+0x3f1/0x480
[ 97.357106] Modules linked in:
[ 97.358488] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 6.9.0-g699646734ab5-dirty #14
[ 97.361556] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
[ 97.363880] RIP: 0010:kprobe_trace_self_tests_init+0x3f1/0x480
[ 97.365538] Code: a8 24 08 82 e9 ae fd ff ff 90 0f 0b 90 48 c7 c7 e5 aa 0b 82 e9 ee fc ff ff 90 0f 0b 90 48 c7 c7 2d 61 06 82 e9 8e fd ff ff 90 <0f> 0b 90 48 c7 c7 33 0b 0c 82 89 c6 e8 6e 03 1f ff 41 ff c7 e9 90
[ 97.370429] RSP: 0000:ffffc90000013b50 EFLAGS: 00010286
[ 97.371852] RAX: 00000000fffffff0 RBX: ffff888005919c00 RCX: 0000000000000000
[ 97.373829] RDX: ffff888003f40000 RSI: ffffffff8236a598 RDI: ffff888003f40a68
[ 97.375715] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
[ 97.377675] R10: ffffffff811c9ae5 R11: ffffffff8120c4e0 R12: 0000000000000000
[ 97.379591] R13: 0000000000000001 R14: 0000000000000015 R15: 0000000000000000
[ 97.381536] FS: 0000000000000000(0000) GS:ffff88807dcc0000(0000) knlGS:0000000000000000
[ 97.383813] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 97.385449] CR2: 0000000000000000 CR3: 0000000002244000 CR4: 00000000000006b0
[ 97.387347] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 97.389277] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 97.391196] Call Trace:
[ 97.391967] <TASK>
[ 97.392647] ? __warn+0xcc/0x180
[ 97.393640] ? kprobe_trace_self_tests_init+0x3f1/0x480
[ 97.395181] ? report_bug+0xbd/0x150
[ 97.396234] ? handle_bug+0x3e/0x60
[ 97.397311] ? exc_invalid_op+0x1a/0x50
[ 97.398434] ? asm_exc_invalid_op+0x1a/0x20
[ 97.399652] ? trace_kprobe_is_busy+0x20/0x20
[ 97.400904] ? tracing_reset_all_online_cpus+0x15/0x90
[ 97.402304] ? kprobe_trace_self_tests_init+0x3f1/0x480
[ 97.403773] ? init_kprobe_trace+0x50/0x50
[ 97.404972] do_one_initcall+0x112/0x240
[ 97.406113] do_initcall_level+0x95/0xb0
[ 97.407286] ? kernel_init+0x1a/0x1a0
[ 97.408401] do_initcalls+0x3f/0x70
[ 97.409452] kernel_init_freeable+0x16f/0x1e0
[ 97.410662] ? rest_init+0x1f0/0x1f0
[ 97.411738] kernel_init+0x1a/0x1a0
[ 97.412788] ret_from_fork+0x39/0x50
[ 97.413817] ? rest_init+0x1f0/0x1f0
[ 97.414844] ret_from_fork_asm+0x11/0x20
[ 97.416285] </TASK>
[ 97.417134] irq event stamp: 13437323
[ 97.418376] hardirqs last enabled at (13437337): [<ffffffff8110bc0c>] console_unlock+0x11c/0x150
[ 97.421285] hardirqs last disabled at (13437370): [<ffffffff8110bbf1>] console_unlock+0x101/0x150
[ 97.423838] softirqs last enabled at (13437366): [<ffffffff8108e17f>] handle_softirqs+0x23f/0x2a0
[ 97.426450] softirqs last disabled at (13437393): [<ffffffff8108e346>] __irq_exit_rcu+0x66/0xd0
[ 97.428850] ---[ end trace 0000000000000000 ]---
And also, since we can not cleanup dynamic_event file, ftracetest are
failed too.
To avoid these issues, build these tests only as modules.
Link: https://lore.kernel.org/all/171811263754.85078.5877446624311852525.stgit@devnote2/
Fixes: 9fe41efaca08 ("tracing: Add synth event generation test module")
Fixes: 64836248dda2 ("tracing: Add kprobe event command generation test module")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
Pull probes updates from Masami Hiramatsu:
- tracing/probes: Add new pseudo-types %pd and %pD support for dumping
dentry name from 'struct dentry *' and file name from 'struct file *'
- uprobes performance optimizations:
- Speed up the BPF uprobe event by delaying the fetching of the
uprobe event arguments that are not used in BPF
- Avoid locking by speculatively checking whether uprobe event is
valid
- Reduce lock contention by using read/write_lock instead of
spinlock for uprobe list operation. This improved BPF uprobe
benchmark result 43% on average
- rethook: Remove non-fatal warning messages when tracing stack from
BPF and skip rcu_is_watching() validation in rethook if possible
- objpool: Optimize objpool (which is used by kretprobes and fprobe as
rethook backend storage) by inlining functions and avoid caching
nr_cpu_ids because it is a const value
- fprobe: Add entry/exit callbacks types (code cleanup)
- kprobes: Check ftrace was killed in kprobes if it uses ftrace
* tag 'probes-v6.10' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
kprobe/ftrace: bail out if ftrace was killed
selftests/ftrace: Fix required features for VFS type test case
objpool: cache nr_possible_cpus() and avoid caching nr_cpu_ids
objpool: enable inlining objpool_push() and objpool_pop() operations
rethook: honor CONFIG_FTRACE_VALIDATE_RCU_IS_WATCHING in rethook_try_get()
ftrace: make extra rcu_is_watching() validation check optional
uprobes: reduce contention on uprobes_tree access
rethook: Remove warning messages printed for finding return address of a frame.
fprobe: Add entry/exit callbacks types
selftests/ftrace: add fprobe test cases for VFS type "%pd" and "%pD"
selftests/ftrace: add kprobe test cases for VFS type "%pd" and "%pD"
Documentation: tracing: add new type '%pd' and '%pD' for kprobe
tracing/probes: support '%pD' type for print struct file's name
tracing/probes: support '%pd' type for print struct dentry's name
uprobes: add speculative lockless system-wide uprobe filter check
uprobes: prepare uprobe args buffer lazily
uprobes: encapsulate preparation of uprobe args buffer
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Pull RCU updates from Uladzislau Rezki:
- Fix a lockdep complain for lazy-preemptible kernel, remove redundant
BH disable for TINY_RCU, remove redundant READ_ONCE() in tree.c, fix
false positives KCSAN splat and fix buffer overflow in the
print_cpu_stall_info().
- Misc updates related to bpf, tracing and update the MAINTAINERS file.
- An improvement of a normal synchronize_rcu() call in terms of
latency. It maintains a separate track for sync. users only. This
approach bypasses per-cpu nocb-lists thus sync-users do not depend on
nocb-list length and how fast regular callbacks are processed.
- RCU tasks: switch tasks RCU grace periods to sleep at TASK_IDLE
priority, fix some comments, add some diagnostic warning to the
exit_tasks_rcu_start() and fix a buffer overflow in the
show_rcu_tasks_trace_gp_kthread().
- RCU torture: Increase memory to guest OS, fix a Tasks Rude RCU
testing, some updates for TREE09, dump mode information to debug GP
kthread state, remove redundant READ_ONCE(), fix some comments about
RCU_TORTURE_PIPE_LEN and pipe_count, remove some redundant pointer
initialization, fix a hung splat task by when the rcutorture tests
start to exit, fix invalid context warning, add '--do-kvfree'
parameter to torture test and use slow register unregister callbacks
only for rcutype test.
* tag 'rcu.next.v6.10' of https://github.com/urezki/linux: (48 commits)
rcutorture: Use rcu_gp_slow_register/unregister() only for rcutype test
torture: Scale --do-kvfree test time
rcutorture: Fix invalid context warning when enable srcu barrier testing
rcutorture: Make stall-tasks directly exit when rcutorture tests end
rcutorture: Removing redundant function pointer initialization
rcutorture: Make rcutorture support print rcu-tasks gp state
rcutorture: Use the gp_kthread_dbg operation specified by cur_ops
rcutorture: Re-use value stored to ->rtort_pipe_count instead of re-reading
rcutorture: Fix rcu_torture_one_read() pipe_count overflow comment
rcutorture: Remove extraneous rcu_torture_pipe_update_one() READ_ONCE()
rcu: Allocate WQ with WQ_MEM_RECLAIM bit set
rcu: Support direct wake-up of synchronize_rcu() users
rcu: Add a trace event for synchronize_rcu_normal()
rcu: Reduce synchronize_rcu() latency
rcu: Fix buffer overflow in print_cpu_stall_info()
rcu: Mollify sparse with RCU guard
rcu-tasks: Fix show_rcu_tasks_trace_gp_kthread buffer overflow
rcu-tasks: Fix the comments for tasks_rcu_exit_srcu_stall_timer
rcu-tasks: Replace exit_tasks_rcu_start() initialization with WARN_ON_ONCE()
rcu: Remove redundant CONFIG_PROVE_RCU #if condition
...
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Introduce CONFIG_FTRACE_VALIDATE_RCU_IS_WATCHING config option to
control whether ftrace low-level code performs additional
rcu_is_watching()-based validation logic in an attempt to catch noinstr
violations.
This check is expected to never be true and is mostly useful for
low-level validation of ftrace subsystem invariants. For most users it
should probably be kept disabled to eliminate unnecessary runtime
overhead.
This improves BPF multi-kretprobe (relying on ftrace and rethook
infrastructure) runtime throughput by 2%, according to BPF benchmarks ([0]).
[0] https://lore.kernel.org/bpf/CAEf4BzauQ2WKMjZdc9s0rBWa01BYbgwHN6aNDXQSHYia47pQ-w@mail.gmail.com/
Link: https://lore.kernel.org/all/20240418190909.704286-1-andrii@kernel.org/
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
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Fix FTRACE_RECORD_RECURSION_SIZE entry, replace tab with
a space character. It helps Kconfig parsers to read file
without error.
Link: https://lore.kernel.org/linux-trace-kernel/20240322121801.1803948-1-ppandit@redhat.com
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fixes: 773c16705058 ("ftrace: Add recording of functions that caused recursion")
Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Currently, if a Kconfig option depends on TASKS_RCU, it conditionally does
"select TASKS_RCU if PREEMPTION". This works, but requires any change in
this enablement logic to be replicated across all such "select" clauses.
A new NEED_TASKS_RCU Kconfig option has been created to allow this
enablement logic to be in one place in kernel/rcu/Kconfig.
Therefore, select the new NEED_TASKS_RCU Kconfig option instead of the
old TASKS_RCU option.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: <linux-trace-kernel@vger.kernel.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
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git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
Pull probes updates from Masami Hiramatsu:
- fprobe: Pass return address to the fprobe entry/exit callbacks so
that the callbacks don't need to analyze pt_regs/stack to find the
function return address.
- kprobe events: cleanup usage of TPARG_FL_FENTRY and TPARG_FL_RETURN
flags so that those are not set at once.
- fprobe events:
- Add a new fprobe events for tracing arbitrary function entry and
exit as a trace event.
- Add a new tracepoint events for tracing raw tracepoint as a
trace event. This allows user to trace non user-exposed
tracepoints.
- Move eprobe's event parser code into probe event common file.
- Introduce BTF (BPF type format) support to kernel probe (kprobe,
fprobe and tracepoint probe) events so that user can specify
traced function arguments by name. This also applies the type of
argument when fetching the argument.
- Introduce '$arg*' wildcard support if BTF is available. This
expands the '$arg*' meta argument to all function argument
automatically.
- Check the return value types by BTF. If the function returns
'void', '$retval' is rejected.
- Add some selftest script for fprobe events, tracepoint events
and BTF support.
- Update documentation about the fprobe events.
- Some fixes for above features, document and selftests.
- selftests for ftrace (in addition to the new fprobe events):
- Add a test case for multiple consecutive probes in a function
which checks if ftrace based kprobe, optimized kprobe and normal
kprobe can be defined in the same target function.
- Add a test case for optimized probe, which checks whether kprobe
can be optimized or not.
* tag 'probes-v6.5' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing/probes: Fix tracepoint event with $arg* to fetch correct argument
Documentation: Fix typo of reference file name
tracing/probes: Fix to return NULL and keep using current argc
selftests/ftrace: Add new test case which checks for optimized probes
selftests/ftrace: Add new test case which adds multiple consecutive probes in a function
Documentation: tracing/probes: Add fprobe event tracing document
selftests/ftrace: Add BTF arguments test cases
selftests/ftrace: Add tracepoint probe test case
tracing/probes: Add BTF retval type support
tracing/probes: Add $arg* meta argument for all function args
tracing/probes: Support function parameters if BTF is available
tracing/probes: Move event parameter fetching code to common parser
tracing/probes: Add tracepoint support on fprobe_events
selftests/ftrace: Add fprobe related testcases
tracing/probes: Add fprobe events for tracing function entry and exit.
tracing/probes: Avoid setting TPARG_FL_FENTRY and TPARG_FL_RETURN
fprobe: Pass return address to the handlers
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Analyzing system call failures with the function_graph tracer can be a
time-consuming process, particularly when locating the kernel function
that first returns an error in the trace logs. This change aims to
simplify the process by recording the function return value to the
'retval' member of 'ftrace_graph_ret' and printing it when outputting
the trace log.
We have introduced new trace options: funcgraph-retval and
funcgraph-retval-hex. The former controls whether to display the return
value, while the latter controls the display format.
Please note that even if a function's return type is void, a return
value will still be printed. You can simply ignore it.
This patch only establishes the fundamental infrastructure. Subsequent
patches will make this feature available on some commonly used processor
architectures.
Here is an example:
I attempted to attach the demo process to a cpu cgroup, but it failed:
echo `pidof demo` > /sys/fs/cgroup/cpu/test/tasks
-bash: echo: write error: Invalid argument
The strace logs indicate that the write system call returned -EINVAL(-22):
...
write(1, "273\n", 4) = -1 EINVAL (Invalid argument)
...
To capture trace logs during a write system call, use the following
commands:
cd /sys/kernel/debug/tracing/
echo 0 > tracing_on
echo > trace
echo *sys_write > set_graph_function
echo *spin* > set_graph_notrace
echo *rcu* >> set_graph_notrace
echo *alloc* >> set_graph_notrace
echo preempt* >> set_graph_notrace
echo kfree* >> set_graph_notrace
echo $$ > set_ftrace_pid
echo function_graph > current_tracer
echo 1 > options/funcgraph-retval
echo 0 > options/funcgraph-retval-hex
echo 1 > tracing_on
echo `pidof demo` > /sys/fs/cgroup/cpu/test/tasks
echo 0 > tracing_on
cat trace > ~/trace.log
To locate the root cause, search for error code -22 directly in the file
trace.log and identify the first function that returned -22. Once you
have identified this function, examine its code to determine the root
cause.
For example, in the trace log below, cpu_cgroup_can_attach
returned -22 first, so we can focus our analysis on this function to
identify the root cause.
...
1) | cgroup_migrate() {
1) 0.651 us | cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */
1) | cgroup_migrate_execute() {
1) | cpu_cgroup_can_attach() {
1) | cgroup_taskset_first() {
1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */
1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */
1) 0.380 us | sched_rt_can_attach(); /* = 0x0 */
1) 2.335 us | } /* cpu_cgroup_can_attach = -22 */
1) 4.369 us | } /* cgroup_migrate_execute = -22 */
1) 7.143 us | } /* cgroup_migrate = -22 */
...
Link: https://lkml.kernel.org/r/1fc502712c981e0e6742185ba242992170ac9da8.1680954589.git.pengdonglin@sangfor.com.cn
Tested-by: Florian Kauer <florian.kauer@linutronix.de>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Donglin Peng <pengdonglin@sangfor.com.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Support function or tracepoint parameters by name if BTF support is enabled
and the event is for function entry (this feature can be used with kprobe-
events, fprobe-events and tracepoint probe events.)
Note that the BTF variable syntax does not require a prefix. If it starts
with an alphabetic character or an underscore ('_') without a prefix like
'$' and '%', it is considered as a BTF variable.
If you specify only the BTF variable name, the argument name will also
be the same name instead of 'arg*'.
# echo 'p vfs_read count pos' >> dynamic_events
# echo 'f vfs_write count pos' >> dynamic_events
# echo 't sched_overutilized_tp rd overutilized' >> dynamic_events
# cat dynamic_events
p:kprobes/p_vfs_read_0 vfs_read count=count pos=pos
f:fprobes/vfs_write__entry vfs_write count=count pos=pos
t:tracepoints/sched_overutilized_tp sched_overutilized_tp rd=rd overutilized=overutilized
Link: https://lore.kernel.org/all/168507474014.913472.16963996883278039183.stgit@mhiramat.roam.corp.google.com/
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
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Add fprobe events for tracing function entry and exit instead of kprobe
events. With this change, we can continue to trace function entry/exit
even if the CONFIG_KPROBES_ON_FTRACE is not available. Since
CONFIG_KPROBES_ON_FTRACE requires the CONFIG_DYNAMIC_FTRACE_WITH_REGS,
it is not available if the architecture only supports
CONFIG_DYNAMIC_FTRACE_WITH_ARGS. And that means kprobe events can not
probe function entry/exit effectively on such architecture.
But this can be solved if the dynamic events supports fprobe events.
The fprobe event is a new dynamic events which is only for the function
(symbol) entry and exit. This event accepts non register fetch arguments
so that user can trace the function arguments and return values.
The fprobe events syntax is here;
f[:[GRP/][EVENT]] FUNCTION [FETCHARGS]
f[MAXACTIVE][:[GRP/][EVENT]] FUNCTION%return [FETCHARGS]
E.g.
# echo 'f vfs_read $arg1' >> dynamic_events
# echo 'f vfs_read%return $retval' >> dynamic_events
# cat dynamic_events
f:fprobes/vfs_read__entry vfs_read arg1=$arg1
f:fprobes/vfs_read__exit vfs_read%return arg1=$retval
# echo 1 > events/fprobes/enable
# head -n 20 trace | tail
# TASK-PID CPU# ||||| TIMESTAMP FUNCTION
# | | | ||||| | |
sh-142 [005] ...1. 448.386420: vfs_read__entry: (vfs_read+0x4/0x340) arg1=0xffff888007f7c540
sh-142 [005] ..... 448.386436: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=0x1
sh-142 [005] ...1. 448.386451: vfs_read__entry: (vfs_read+0x4/0x340) arg1=0xffff888007f7c540
sh-142 [005] ..... 448.386458: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=0x1
sh-142 [005] ...1. 448.386469: vfs_read__entry: (vfs_read+0x4/0x340) arg1=0xffff888007f7c540
sh-142 [005] ..... 448.386476: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=0x1
sh-142 [005] ...1. 448.602073: vfs_read__entry: (vfs_read+0x4/0x340) arg1=0xffff888007f7c540
sh-142 [005] ..... 448.602089: vfs_read__exit: (ksys_read+0x75/0x100 <- vfs_read) arg1=0x1
Link: https://lore.kernel.org/all/168507469754.913472.6112857614708350210.stgit@mhiramat.roam.corp.google.com/
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/all/202302011530.7vm4O8Ro-lkp@intel.com/
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
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The user events was added a bit prematurely, and there were a few kernel
developers that had issues with it. The API also needed a bit of work to
make sure it would be stable. It was decided to make user events "broken"
until this was settled. Now it has a new API that appears to be as stable
as it will be without the use of a crystal ball. It's being used within
Microsoft as is, which means the API has had some testing in real world
use cases. It went through many discussions in the bi-weekly tracing
meetings, and there's been no more comments about updates.
I feel this is good to go.
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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As part of the discussions for user_events aligned with user space
tracers, it was determined that user programs should register a aligned
value to set or clear a bit when an event becomes enabled. Currently a
shared page is being used that requires mmap(). Remove the shared page
implementation and move to a user registered address implementation.
In this new model during the event registration from user programs 3 new
values are specified. The first is the address to update when the event
is either enabled or disabled. The second is the bit to set/clear to
reflect the event being enabled. The third is the size of the value at
the specified address.
This allows for a local 32/64-bit value in user programs to support
both kernel and user tracers. As an example, setting bit 31 for kernel
tracers when the event becomes enabled allows for user tracers to use
the other bits for ref counts or other flags. The kernel side updates
the bit atomically, user programs need to also update these values
atomically.
User provided addresses must be aligned on a natural boundary, this
allows for single page checking and prevents odd behaviors such as a
enable value straddling 2 pages instead of a single page. Currently
page faults are only logged, future patches will handle these.
Link: https://lkml.kernel.org/r/20230328235219.203-4-beaub@linux.microsoft.com
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Direct called trampolines can be called in two ways:
- either from the ftrace callsite. In this case, they do not access any
struct ftrace_regs nor pt_regs
- Or, if a ftrace ops is also attached, from the end of a ftrace
trampoline. In this case, the call_direct_funcs ops is in charge of
setting the direct call trampoline's address in a struct ftrace_regs
Since:
commit 9705bc709604 ("ftrace: pass fregs to arch_ftrace_set_direct_caller()")
The later case no longer requires a full pt_regs. It only needs a struct
ftrace_regs so DIRECT_CALLS can work with both WITH_ARGS or WITH_REGS.
With architectures like arm64 already abandoning WITH_REGS in favor of
WITH_ARGS, it's important to have DIRECT_CALLS work WITH_ARGS only.
Link: https://lkml.kernel.org/r/20230321140424.345218-7-revest@chromium.org
Signed-off-by: Florent Revest <revest@chromium.org>
Co-developed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
Pull tracing updates from Steven Rostedt:
- Add function names as a way to filter function addresses
- Add sample module to test ftrace ops and dynamic trampolines
- Allow stack traces to be passed from beginning event to end event for
synthetic events. This will allow seeing the stack trace of when a
task is scheduled out and recorded when it gets scheduled back in.
- Add trace event helper __get_buf() to use as a temporary buffer when
printing out trace event output.
- Add kernel command line to create trace instances on boot up.
- Add enabling of events to instances created at boot up.
- Add trace_array_puts() to write into instances.
- Allow boot instances to take a snapshot at the end of boot up.
- Allow live patch modules to include trace events
- Minor fixes and clean ups
* tag 'trace-v6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (31 commits)
tracing: Remove unnecessary NULL assignment
tracepoint: Allow livepatch module add trace event
tracing: Always use canonical ftrace path
tracing/histogram: Fix stacktrace histogram Documententation
tracing/histogram: Fix stacktrace key
tracing/histogram: Fix a few problems with stacktrace variable printing
tracing: Add BUILD_BUG() to make sure stacktrace fits in strings
tracing/histogram: Don't use strlen to find length of stacktrace variables
tracing: Allow boot instances to have snapshot buffers
tracing: Add trace_array_puts() to write into instance
tracing: Add enabling of events to boot instances
tracing: Add creation of instances at boot command line
tracing: Fix trace_event_raw_event_synth() if else statement
samples: ftrace: Make some global variables static
ftrace: sample: avoid open-coded 64-bit division
samples: ftrace: Include the nospec-branch.h only for x86
tracing: Acquire buffer from temparary trace sequence
tracing/histogram: Wrap remaining shell snippets in code blocks
tracing/osnoise: No need for schedule_hrtimeout range
bpf/tracing: Use stage6 of tracing to not duplicate macros
...
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git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
Pull arm64 updates from Catalin Marinas:
- Support for arm64 SME 2 and 2.1. SME2 introduces a new 512-bit
architectural register (ZT0, for the look-up table feature) that
Linux needs to save/restore
- Include TPIDR2 in the signal context and add the corresponding
kselftests
- Perf updates: Arm SPEv1.2 support, HiSilicon uncore PMU updates, ACPI
support to the Marvell DDR and TAD PMU drivers, reset DTM_PMU_CONFIG
(ARM CMN) at probe time
- Support for DYNAMIC_FTRACE_WITH_CALL_OPS on arm64
- Permit EFI boot with MMU and caches on. Instead of cleaning the
entire loaded kernel image to the PoC and disabling the MMU and
caches before branching to the kernel bare metal entry point, leave
the MMU and caches enabled and rely on EFI's cacheable 1:1 mapping of
all of system RAM to populate the initial page tables
- Expose the AArch32 (compat) ELF_HWCAP features to user in an arm64
kernel (the arm32 kernel only defines the values)
- Harden the arm64 shadow call stack pointer handling: stash the shadow
stack pointer in the task struct on interrupt, load it directly from
this structure
- Signal handling cleanups to remove redundant validation of size
information and avoid reading the same data from userspace twice
- Refactor the hwcap macros to make use of the automatically generated
ID registers. It should make new hwcaps writing less error prone
- Further arm64 sysreg conversion and some fixes
- arm64 kselftest fixes and improvements
- Pointer authentication cleanups: don't sign leaf functions, unify
asm-arch manipulation
- Pseudo-NMI code generation optimisations
- Minor fixes for SME and TPIDR2 handling
- Miscellaneous updates: ARCH_FORCE_MAX_ORDER is now selectable,
replace strtobool() to kstrtobool() in the cpufeature.c code, apply
dynamic shadow call stack in two passes, intercept pfn changes in
set_pte_at() without the required break-before-make sequence, attempt
to dump all instructions on unhandled kernel faults
* tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (130 commits)
arm64: fix .idmap.text assertion for large kernels
kselftest/arm64: Don't require FA64 for streaming SVE+ZA tests
kselftest/arm64: Copy whole EXTRA context
arm64: kprobes: Drop ID map text from kprobes blacklist
perf: arm_spe: Print the version of SPE detected
perf: arm_spe: Add support for SPEv1.2 inverted event filtering
perf: Add perf_event_attr::config3
arm64/sme: Fix __finalise_el2 SMEver check
drivers/perf: fsl_imx8_ddr_perf: Remove set-but-not-used variable
arm64/signal: Only read new data when parsing the ZT context
arm64/signal: Only read new data when parsing the ZA context
arm64/signal: Only read new data when parsing the SVE context
arm64/signal: Avoid rereading context frame sizes
arm64/signal: Make interface for restore_fpsimd_context() consistent
arm64/signal: Remove redundant size validation from parse_user_sigframe()
arm64/signal: Don't redundantly verify FPSIMD magic
arm64/cpufeature: Use helper macros to specify hwcaps
arm64/cpufeature: Always use symbolic name for feature value in hwcaps
arm64/sysreg: Initial unsigned annotations for ID registers
arm64/sysreg: Initial annotation of signed ID registers
...
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The canonical location for the tracefs filesystem is at /sys/kernel/tracing.
But, from Documentation/trace/ftrace.rst:
Before 4.1, all ftrace tracing control files were within the debugfs
file system, which is typically located at /sys/kernel/debug/tracing.
For backward compatibility, when mounting the debugfs file system,
the tracefs file system will be automatically mounted at:
/sys/kernel/debug/tracing
Many comments and Kconfig help messages in the tracing code still refer
to this older debugfs path, so let's update them to avoid confusion.
Link: https://lore.kernel.org/linux-trace-kernel/20230215223350.2658616-2-zwisler@google.com
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com>
Signed-off-by: Ross Zwisler <zwisler@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Fix some editorial nits in trace Kconfig.
Link: https://lkml.kernel.org/r/20230124181647.15902-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Architectures without dynamic ftrace trampolines incur an overhead when
multiple ftrace_ops are enabled with distinct filters. in these cases,
each call site calls a common trampoline which uses
ftrace_ops_list_func() to iterate over all enabled ftrace functions, and
so incurs an overhead relative to the size of this list (including RCU
protection overhead).
Architectures with dynamic ftrace trampolines avoid this overhead for
call sites which have a single associated ftrace_ops. In these cases,
the dynamic trampoline is customized to branch directly to the relevant
ftrace function, avoiding the list overhead.
On some architectures it's impractical and/or undesirable to implement
dynamic ftrace trampolines. For example, arm64 has limited branch ranges
and cannot always directly branch from a call site to an arbitrary
address (e.g. from a kernel text address to an arbitrary module
address). Calls from modules to core kernel text can be indirected via
PLTs (allocated at module load time) to address this, but the same is
not possible from calls from core kernel text.
Using an indirect branch from a call site to an arbitrary trampoline is
possible, but requires several more instructions in the function
prologue (or immediately before it), and/or comes with far more complex
requirements for patching.
Instead, this patch adds a new option, where an architecture can
associate each call site with a pointer to an ftrace_ops, placed at a
fixed offset from the call site. A shared trampoline can recover this
pointer and call ftrace_ops::func() without needing to go via
ftrace_ops_list_func(), avoiding the associated overhead.
This avoids issues with branch range limitations, and avoids the need to
allocate and manipulate dynamic trampolines, making it far simpler to
implement and maintain, while having similar performance
characteristics.
Note that this allows for dynamic ftrace_ops to be invoked directly from
an architecture's ftrace_caller trampoline, whereas existing code forces
the use of ftrace_ops_get_list_func(), which is in part necessary to
permit the ftrace_ops to be freed once unregistered *and* to avoid
branch/address-generation range limitation on some architectures (e.g.
where ops->func is a module address, and may be outside of the direct
branch range for callsites within the main kernel image).
The CALL_OPS approach avoids this problems and is safe as:
* The existing synchronization in ftrace_shutdown() using
ftrace_shutdown() using synchronize_rcu_tasks_rude() (and
synchronize_rcu_tasks()) ensures that no tasks hold a stale reference
to an ftrace_ops (e.g. in the middle of the ftrace_caller trampoline,
or while invoking ftrace_ops::func), when that ftrace_ops is
unregistered.
Arguably this could also be relied upon for the existing scheme,
permitting dynamic ftrace_ops to be invoked directly when ops->func is
in range, but this will require additional logic to handle branch
range limitations, and is not handled by this patch.
* Each callsite's ftrace_ops pointer literal can hold any valid kernel
address, and is updated atomically. As an architecture's ftrace_caller
trampoline will atomically load the ops pointer then dereference
ops->func, there is no risk of invoking ops->func with a mismatches
ops pointer, and updates to the ops pointer do not require special
care.
A subsequent patch will implement architectures support for arm64. There
should be no functional change as a result of this patch alone.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Florent Revest <revest@chromium.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230123134603.1064407-2-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux
Pull powerpc updates from Michael Ellerman:
- Add powerpc qspinlock implementation optimised for large system
scalability and paravirt. See the merge message for more details
- Enable objtool to be built on powerpc to generate mcount locations
- Use a temporary mm for code patching with the Radix MMU, so the
writable mapping is restricted to the patching CPU
- Add an option to build the 64-bit big-endian kernel with the ELFv2
ABI
- Sanitise user registers on interrupt entry on 64-bit Book3S
- Many other small features and fixes
Thanks to Aboorva Devarajan, Angel Iglesias, Benjamin Gray, Bjorn
Helgaas, Bo Liu, Chen Lifu, Christoph Hellwig, Christophe JAILLET,
Christophe Leroy, Christopher M. Riedl, Colin Ian King, Deming Wang,
Disha Goel, Dmitry Torokhov, Finn Thain, Geert Uytterhoeven, Gustavo A.
R. Silva, Haowen Bai, Joel Stanley, Jordan Niethe, Julia Lawall, Kajol
Jain, Laurent Dufour, Li zeming, Miaoqian Lin, Michael Jeanson, Nathan
Lynch, Naveen N. Rao, Nayna Jain, Nicholas Miehlbradt, Nicholas Piggin,
Pali Rohár, Randy Dunlap, Rohan McLure, Russell Currey, Sathvika
Vasireddy, Shaomin Deng, Stephen Kitt, Stephen Rothwell, Thomas
Weißschuh, Tiezhu Yang, Uwe Kleine-König, Xie Shaowen, Xiu Jianfeng,
XueBing Chen, Yang Yingliang, Zhang Jiaming, ruanjinjie, Jessica Yu,
and Wolfram Sang.
* tag 'powerpc-6.2-1' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux: (181 commits)
powerpc/code-patching: Fix oops with DEBUG_VM enabled
powerpc/qspinlock: Fix 32-bit build
powerpc/prom: Fix 32-bit build
powerpc/rtas: mandate RTAS syscall filtering
powerpc/rtas: define pr_fmt and convert printk call sites
powerpc/rtas: clean up includes
powerpc/rtas: clean up rtas_error_log_max initialization
powerpc/pseries/eeh: use correct API for error log size
powerpc/rtas: avoid scheduling in rtas_os_term()
powerpc/rtas: avoid device tree lookups in rtas_os_term()
powerpc/rtasd: use correct OF API for event scan rate
powerpc/rtas: document rtas_call()
powerpc/pseries: unregister VPA when hot unplugging a CPU
powerpc/pseries: reset the RCU watchdogs after a LPM
powerpc: Take in account addition CPU node when building kexec FDT
powerpc: export the CPU node count
powerpc/cpuidle: Set CPUIDLE_FLAG_POLLING for snooze state
powerpc/dts/fsl: Fix pca954x i2c-mux node names
cxl: Remove unnecessary cxl_pci_window_alignment()
selftests/powerpc: Fix resource leaks
...
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git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
Pull tracing updates from Steven Rostedt:
- Add options to the osnoise tracer:
- 'panic_on_stop' option that panics the kernel if osnoise is
greater than some user defined threshold.
- 'preempt' option, to test noise while preemption is disabled
- 'irq' option, to test noise when interrupts are disabled
- Add .percent and .graph suffix to histograms to give different
outputs
- Add nohitcount to disable showing hitcount in histogram output
- Add new __cpumask() to trace event fields to annotate that a unsigned
long array is a cpumask to user space and should be treated as one.
- Add trace_trigger kernel command line parameter to enable trace event
triggers at boot up. Useful to trace stack traces, disable tracing
and take snapshots.
- Fix x86/kmmio mmio tracer to work with the updates to lockdep
- Unify the panic and die notifiers
- Add back ftrace_expect reference that is used to extract more
information in the ftrace_bug() code.
- Have trigger filter parsing errors show up in the tracing error log.
- Updated MAINTAINERS file to add kernel tracing mailing list and
patchwork info
- Use IDA to keep track of event type numbers.
- And minor fixes and clean ups
* tag 'trace-v6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (44 commits)
tracing: Fix cpumask() example typo
tracing: Improve panic/die notifiers
ftrace: Prevent RCU stall on PREEMPT_VOLUNTARY kernels
tracing: Do not synchronize freeing of trigger filter on boot up
tracing: Remove pointer (asterisk) and brackets from cpumask_t field
tracing: Have trigger filter parsing errors show up in error_log
x86/mm/kmmio: Remove redundant preempt_disable()
tracing: Fix infinite loop in tracing_read_pipe on overflowed print_trace_line
Documentation/osnoise: Add osnoise/options documentation
tracing/osnoise: Add preempt and/or irq disabled options
tracing/osnoise: Add PANIC_ON_STOP option
Documentation/osnoise: Escape underscore of NO_ prefix
tracing: Fix some checker warnings
tracing/osnoise: Make osnoise_options static
tracing: remove unnecessary trace_trigger ifdef
ring-buffer: Handle resize in early boot up
tracing/hist: Fix issue of losting command info in error_log
tracing: Fix issue of missing one synthetic field
tracing/hist: Fix out-of-bound write on 'action_data.var_ref_idx'
tracing/hist: Fix wrong return value in parse_action_params()
...
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Both CONFIG_OSNOISE_TRACER and CONFIG_HWLAT_TRACER partially enables the
CONFIG_TRACER_MAX_TRACE code, but that is complicated and has
introduced a bug; It declares tracing_max_lat_fops data structure outside
of #ifdefs, but since it is defined only when CONFIG_TRACER_MAX_TRACE=y
or CONFIG_HWLAT_TRACER=y, if only CONFIG_OSNOISE_TRACER=y, that
declaration comes to a definition(!).
To fix this issue, and do not repeat the similar problem, makes
CONFIG_OSNOISE_TRACER and CONFIG_HWLAT_TRACER enables the
CONFIG_TRACER_MAX_TRACE always. It has there benefits;
- Fix the tracing_max_lat_fops bug
- Simplify the #ifdefs
- CONFIG_TRACER_MAX_TRACE code is fully enabled, or not.
Link: https://lore.kernel.org/linux-trace-kernel/167033628155.4111793.12185405690820208159.stgit@devnote3
Fixes: 424b650f35c7 ("tracing: Fix missing osnoise tracer on max_latency")
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: stable@vger.kernel.org
Reported-by: David Howells <dhowells@redhat.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Link: https://lore.kernel.org/all/166992525941.1716618.13740663757583361463.stgit@warthog.procyon.org.uk/ (original thread and v1)
Link: https://lore.kernel.org/all/202212052253.VuhZ2ulJ-lkp@intel.com/T/#u (v1 error report)
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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In subsequent patches we'll arrange for architectures to have an
ftrace_regs which is entirely distinct from pt_regs. In preparation for
this, we need to minimize the use of pt_regs to where strictly necessary
in the core ftrace code.
This patch adds new ftrace_regs_{get,set}_*() helpers which can be used
to manipulate ftrace_regs. When CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS=y,
these can always be used on any ftrace_regs, and when
CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS=n these can be used when regs are
available. A new ftrace_regs_has_args(fregs) helper is added which code
can use to check when these are usable.
Co-developed-by: Florent Revest <revest@chromium.org>
Signed-off-by: Florent Revest <revest@chromium.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20221103170520.931305-4-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
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Some architectures (powerpc) may not support ftrace locations being nop'ed
out at build time. Introduce CONFIG_HAVE_OBJTOOL_NOP_MCOUNT for objtool, as
a means for architectures to enable nop'ing of ftrace locations. Add --mnop
as an option to objtool --mcount, to indicate support for the same.
Also, make sure that --mnop can be passed as an option to objtool only when
--mcount is passed.
Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221114175754.1131267-12-sv@linux.ibm.com
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x86 will shortly start using -fpatchable-function-entry for purposes
other than ftrace, make sure the __patchable_function_entry section
isn't merged in the mcount_loc section.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220903131154.420467-2-jolsa@kernel.org
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RV is a lightweight (yet rigorous) method that complements classical
exhaustive verification techniques (such as model checking and
theorem proving) with a more practical approach to complex systems.
RV works by analyzing the trace of the system's actual execution,
comparing it against a formal specification of the system behavior.
RV can give precise information on the runtime behavior of the
monitored system while enabling the reaction for unexpected
events, avoiding, for example, the propagation of a failure on
safety-critical systems.
The development of this interface roots in the development of the
paper:
De Oliveira, Daniel Bristot; Cucinotta, Tommaso; De Oliveira, Romulo
Silva. Efficient formal verification for the Linux kernel. In:
International Conference on Software Engineering and Formal Methods.
Springer, Cham, 2019. p. 315-332.
And:
De Oliveira, Daniel Bristot. Automata-based formal analysis
and verification of the real-time Linux kernel. PhD Thesis, 2020.
The RV interface resembles the tracing/ interface on purpose. The current
path for the RV interface is /sys/kernel/tracing/rv/.
It presents these files:
"available_monitors"
- List the available monitors, one per line.
For example:
# cat available_monitors
wip
wwnr
"enabled_monitors"
- Lists the enabled monitors, one per line;
- Writing to it enables a given monitor;
- Writing a monitor name with a '!' prefix disables it;
- Truncating the file disables all enabled monitors.
For example:
# cat enabled_monitors
# echo wip > enabled_monitors
# echo wwnr >> enabled_monitors
# cat enabled_monitors
wip
wwnr
# echo '!wip' >> enabled_monitors
# cat enabled_monitors
wwnr
# echo > enabled_monitors
# cat enabled_monitors
#
Note that more than one monitor can be enabled concurrently.
"monitoring_on"
- It is an on/off general switcher for monitoring. Note
that it does not disable enabled monitors or detach events,
but stop the per-entity monitors of monitoring the events
received from the system. It resembles the "tracing_on" switcher.
"monitors/"
Each monitor will have its one directory inside "monitors/". There
the monitor specific files will be presented.
The "monitors/" directory resembles the "events" directory on
tracefs.
For example:
# cd monitors/wip/
# ls
desc enable
# cat desc
wakeup in preemptive per-cpu testing monitor.
# cat enable
0
For further information, see the comments in the header of
kernel/trace/rv/rv.c from this patch.
Link: https://lkml.kernel.org/r/a4bfe038f50cb047bfb343ad0e12b0e646ab308b.1659052063.git.bristot@kernel.org
Cc: Wim Van Sebroeck <wim@linux-watchdog.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Gabriele Paoloni <gpaoloni@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Tao Zhou <tao.zhou@linux.dev>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-trace-devel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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It was brought up that on ARMv7, that because the FUNCTION_TRACER does not
use nops to keep function tracing disabled because of the use of a link
register, it does have some performance impact.
The start of functions when -pg is used to compile the kernel is:
push {lr}
bl 8010e7c0 <__gnu_mcount_nc>
When function tracing is tuned off, it becomes:
push {lr}
add sp, sp, #4
Which just puts the stack back to its normal location. But these two
instructions at the start of every function does incur some overhead.
Be more honest in the Kconfig FUNCTION_TRACER description and specify that
the overhead being in the noise was x86 specific, but other architectures
may vary.
Link: https://lore.kernel.org/all/20220705105416.GE5208@pengutronix.de/
Link: https://lkml.kernel.org/r/20220706161231.085a83da@gandalf.local.home
Reported-by: Sascha Hauer <sha@pengutronix.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
|
