linux.git/kernel/trace/trace_events_hist.c, branch v6.12.80

tracing: Fix checking of freed trace_event_file for hist files

2026-03-04T12:21:59+00:00

[ Upstream commit f0a0da1f907e8488826d91c465f7967a56a95aca ]

The event_hist_open() and event_hist_poll() functions currently retrieve
a trace_event_file pointer from a file struct by invoking
event_file_data(), which simply returns file->f_inode->i_private. The
functions then check if the pointer is NULL to determine whether the event
is still valid. This approach is flawed because i_private is assigned when
an eventfs inode is allocated and remains set throughout its lifetime.
Instead, the code should call event_file_file(), which checks for
EVENT_FILE_FL_FREED. Using the incorrect access function may result in the
code potentially opening a hist file for an event that is being removed or
becoming stuck while polling on this file.

Correct the access method to event_file_file() in both functions.

Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers 
Cc: Tom Zanussi 
Link: https://patch.msgid.link/20260219162737.314231-2-petr.pavlu@suse.com
Fixes: 1bd13edbbed6 ("tracing/hist: Add poll(POLLIN) support on hist file")
Signed-off-by: Petr Pavlu 
Acked-by: Masami Hiramatsu (Google) 
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Sasha Levin

tracing: Properly process error handling in event_hist_trigger_parse()

2026-03-04T12:20:24+00:00

[ Upstream commit 0550069cc25f513ce1f109c88f7c1f01d63297db ]

Memory allocated with trigger_data_alloc() requires trigger_data_free()
for proper cleanup.

Replace kfree() with trigger_data_free() to fix this.

Found via static analysis and code review.

This isn't a real bug due to the current code basically being an open
coded version of trigger_data_free() without the synchronization. The
synchronization isn't needed as this is the error path of creation and
there's nothing to synchronize against yet. Replace the kfree() to be
consistent with the allocation.

Cc: Masami Hiramatsu 
Cc: Mathieu Desnoyers 
Cc: Tom Zanussi 
Link: https://patch.msgid.link/20251211100058.2381268-1-linmq006@gmail.com
Fixes: e1f187d09e11 ("tracing: Have existing event_command.parse() implementations use helpers")
Signed-off-by: Miaoqian Lin 
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Sasha Levin

tracing: Fix crash on synthetic stacktrace field usage

2026-01-30T09:28:46+00:00

commit 90f9f5d64cae4e72defd96a2a22760173cb3c9ec upstream.

When creating a synthetic event based on an existing synthetic event that
had a stacktrace field and the new synthetic event used that field a
kernel crash occurred:

 ~# cd /sys/kernel/tracing
 ~# echo 's:stack unsigned long stack[];' > dynamic_events
 ~# echo 'hist:keys=prev_pid:s0=common_stacktrace if prev_state & 3' >> events/sched/sched_switch/trigger
 ~# echo 'hist:keys=next_pid:s1=$s0:onmatch(sched.sched_switch).trace(stack,$s1)' >> events/sched/sched_switch/trigger

The above creates a synthetic event that takes a stacktrace when a task
schedules out in a non-running state and passes that stacktrace to the
sched_switch event when that task schedules back in. It triggers the
"stack" synthetic event that has a stacktrace as its field (called "stack").

 ~# echo 's:syscall_stack s64 id; unsigned long stack[];' >> dynamic_events
 ~# echo 'hist:keys=common_pid:s2=stack' >> events/synthetic/stack/trigger
 ~# echo 'hist:keys=common_pid:s3=$s2,i0=id:onmatch(synthetic.stack).trace(syscall_stack,$i0,$s3)' >> events/raw_syscalls/sys_exit/trigger

The above makes another synthetic event called "syscall_stack" that
attaches the first synthetic event (stack) to the sys_exit trace event and
records the stacktrace from the stack event with the id of the system call
that is exiting.

When enabling this event (or using it in a historgram):

 ~# echo 1 > events/synthetic/syscall_stack/enable

Produces a kernel crash!

 BUG: unable to handle page fault for address: 0000000000400010
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: Oops: 0000 [#1] SMP PTI
 CPU: 6 UID: 0 PID: 1257 Comm: bash Not tainted 6.16.3+deb14-amd64 #1 PREEMPT(lazy)  Debian 6.16.3-1
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
 RIP: 0010:trace_event_raw_event_synth+0x90/0x380
 Code: c5 00 00 00 00 85 d2 0f 84 e1 00 00 00 31 db eb 34 0f 1f 00 66 66 2e 0f 1f 84 00 00 00 00 00 66 66 2e 0f 1f 84 00 00 00 00 00 <49> 8b 04 24 48 83 c3 01 8d 0c c5 08 00 00 00 01 cd 41 3b 5d 40 0f
 RSP: 0018:ffffd2670388f958 EFLAGS: 00010202
 RAX: ffff8ba1065cc100 RBX: 0000000000000000 RCX: 0000000000000000
 RDX: 0000000000000001 RSI: fffff266ffda7b90 RDI: ffffd2670388f9b0
 RBP: 0000000000000010 R08: ffff8ba104e76000 R09: ffffd2670388fa50
 R10: ffff8ba102dd42e0 R11: ffffffff9a908970 R12: 0000000000400010
 R13: ffff8ba10a246400 R14: ffff8ba10a710220 R15: fffff266ffda7b90
 FS:  00007fa3bc63f740(0000) GS:ffff8ba2e0f48000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000400010 CR3: 0000000107f9e003 CR4: 0000000000172ef0
 Call Trace:
  
  ? __tracing_map_insert+0x208/0x3a0
  action_trace+0x67/0x70
  event_hist_trigger+0x633/0x6d0
  event_triggers_call+0x82/0x130
  trace_event_buffer_commit+0x19d/0x250
  trace_event_raw_event_sys_exit+0x62/0xb0
  syscall_exit_work+0x9d/0x140
  do_syscall_64+0x20a/0x2f0
  ? trace_event_raw_event_sched_switch+0x12b/0x170
  ? save_fpregs_to_fpstate+0x3e/0x90
  ? _raw_spin_unlock+0xe/0x30
  ? finish_task_switch.isra.0+0x97/0x2c0
  ? __rseq_handle_notify_resume+0xad/0x4c0
  ? __schedule+0x4b8/0xd00
  ? restore_fpregs_from_fpstate+0x3c/0x90
  ? switch_fpu_return+0x5b/0xe0
  ? do_syscall_64+0x1ef/0x2f0
  ? do_fault+0x2e9/0x540
  ? __handle_mm_fault+0x7d1/0xf70
  ? count_memcg_events+0x167/0x1d0
  ? handle_mm_fault+0x1d7/0x2e0
  ? do_user_addr_fault+0x2c3/0x7f0
  entry_SYSCALL_64_after_hwframe+0x76/0x7e

The reason is that the stacktrace field is not labeled as such, and is
treated as a normal field and not as a dynamic event that it is.

In trace_event_raw_event_synth() the event is field is still treated as a
dynamic array, but the retrieval of the data is considered a normal field,
and the reference is just the meta data:

// Meta data is retrieved instead of a dynamic array
  str_val = (char *)(long)var_ref_vals[val_idx];

// Then when it tries to process it:
  len = *((unsigned long *)str_val) + 1;

It triggers a kernel page fault.

To fix this, first when defining the fields of the first synthetic event,
set the filter type to FILTER_STACKTRACE. This is used later by the second
synthetic event to know that this field is a stacktrace. When creating
the field of the new synthetic event, have it use this FILTER_STACKTRACE
to know to create a stacktrace field to copy the stacktrace into.

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu 
Cc: Mathieu Desnoyers 
Cc: Tom Zanussi 
Link: https://patch.msgid.link/20260122194824.6905a38e@gandalf.local.home
Fixes: 00cf3d672a9d ("tracing: Allow synthetic events to pass around stacktraces")
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Greg Kroah-Hartman

tracing: Fix memory leaks in create_field_var()

2025-11-13T20:34:39+00:00

[ Upstream commit 80f0d631dcc76ee1b7755bfca1d8417d91d71414 ]

The function create_field_var() allocates memory for 'val' through
create_hist_field() inside parse_atom(), and for 'var' through
create_var(), which in turn allocates var->type and var->var.name
internally. Simply calling kfree() to release these structures will
result in memory leaks.

Use destroy_hist_field() to properly free 'val', and explicitly release
the memory of var->type and var->var.name before freeing 'var' itself.

Link: https://patch.msgid.link/20251106120132.3639920-1-zilin@seu.edu.cn
Fixes: 02205a6752f22 ("tracing: Add support for 'field variables'")
Signed-off-by: Zilin Guan 
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Sasha Levin

tracing: Rename event_trigger_alloc() to trigger_data_alloc()

2025-06-19T13:31:48+00:00

[ Upstream commit f2947c4b7d0f235621c5daf78aecfbd6e22c05e5 ]

The function event_trigger_alloc() creates an event_trigger_data
descriptor and states that it needs to be freed via event_trigger_free().
This is incorrect, it needs to be freed by trigger_data_free() as
event_trigger_free() adds ref counting.

Rename event_trigger_alloc() to trigger_data_alloc() and state that it
needs to be freed via trigger_data_free(). This naming convention
was introducing bugs.

Cc: Masami Hiramatsu 
Cc: Mark Rutland 
Cc: Mathieu Desnoyers 
Cc: Andrew Morton 
Cc: Tom Zanussi 
Link: https://lore.kernel.org/20250507145455.776436410@goodmis.org
Fixes: 86599dbe2c527 ("tracing: Add helper functions to simplify event_command.parse() callback handling")
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Sasha Levin

tracing: Move histogram trigger variables from stack to per CPU structure

2025-06-19T13:31:46+00:00

[ Upstream commit 7ab0fc61ce73040f89b12d76a8279995ec283541 ]

The histogram trigger has three somewhat large arrays on the kernel stack:

	unsigned long entries[HIST_STACKTRACE_DEPTH];
	u64 var_ref_vals[TRACING_MAP_VARS_MAX];
	char compound_key[HIST_KEY_SIZE_MAX];

Checking the function event_hist_trigger() stack frame size, it currently
uses 816 bytes for its stack frame due to these variables!

Instead, allocate a per CPU structure that holds these arrays for each
context level (normal, softirq, irq and NMI). That is, each CPU will have
4 of these structures. This will be allocated when the first histogram
trigger is enabled and freed when the last is disabled. When the
histogram callback triggers, it will request this structure. The request
will disable preemption, get the per CPU structure at the index of the
per CPU variable, and increment that variable.

The callback will use the arrays in this structure to perform its work and
then release the structure. That in turn will simply decrement the per CPU
index and enable preemption.

Moving the variables from the kernel stack to the per CPU structure brings
the stack frame of event_hist_trigger() down to just 112 bytes.

Cc: Mathieu Desnoyers 
Cc: Tom Zanussi 
Link: https://lore.kernel.org/20250407123851.74ea8d58@gandalf.local.home
Fixes: 067fe038e70f6 ("tracing: Add variable reference handling to hist triggers")
Reviewed-by: Masami Hiramatsu (Google) 
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Sasha Levin

tracing: Correct the refcount if the hist/hist_debug file fails to open

2025-04-10T12:39:35+00:00

[ Upstream commit 0b4ffbe4888a2c71185eaf5c1a02dd3586a9bc04 ]

The function event_{hist,hist_debug}_open() maintains the refcount of
'file->tr' and 'file' through tracing_open_file_tr(). However, it does
not roll back these counts on subsequent failure paths, resulting in a
refcount leak.

A very obvious case is that if the hist/hist_debug file belongs to a
specific instance, the refcount leak will prevent the deletion of that
instance, as it relies on the condition 'tr->ref == 1' within
__remove_instance().

Fix this by calling tracing_release_file_tr() on all failure paths in
event_{hist,hist_debug}_open() to correct the refcount.

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu 
Cc: Mathieu Desnoyers 
Cc: Zheng Yejian 
Link: https://lore.kernel.org/20250314065335.1202817-1-wutengda@huaweicloud.com
Fixes: 1cc111b9cddc ("tracing: Fix uaf issue when open the hist or hist_debug file")
Signed-off-by: Tengda Wu 
Signed-off-by: Steven Rostedt (Google) 
Signed-off-by: Sasha Levin

tracing/hist: Support POLLPRI event for poll on histogram

2025-04-10T12:39:35+00:00

[ Upstream commit 66fc6f521a0b91051ce6968a216a30bc52267bf8 ]

Since POLLIN will not be flushed until the hist file is read, the user
needs to repeatedly read() and poll() on the hist file for monitoring the
event continuously. But the read() is somewhat redundant when the user is
only monitoring for event updates.

Add POLLPRI poll event on the hist file so the event returns when a
histogram is updated after open(), poll() or read(). Thus it is possible
to wait for the next event without having to issue a read().

Cc: Shuah Khan 
Cc: Mathieu Desnoyers 
Link: https://lore.kernel.org/173527248770.464571.2536902137325258133.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) 
Reviewed-by: Tom Zanussi 
Signed-off-by: Steven Rostedt (Google) 
Stable-dep-of: 0b4ffbe4888a ("tracing: Correct the refcount if the hist/hist_debug file fails to open")
Signed-off-by: Sasha Levin

tracing/hist: Add poll(POLLIN) support on hist file

2025-04-10T12:39:35+00:00

[ Upstream commit 1bd13edbbed6e7e396f1aab92b224a4775218e68 ]

Add poll syscall support on the `hist` file. The Waiter will be waken
up when the histogram is updated with POLLIN.

Currently, there is no way to wait for a specific event in userspace.
So user needs to peek the `trace` periodicaly, or wait on `trace_pipe`.
But it is not a good idea to peek at the `trace` for an event that
randomly happens. And `trace_pipe` is not coming back until a page is
filled with events.

This allows a user to wait for a specific event on the `hist` file. User
can set a histogram trigger on the event which they want to monitor
and poll() on its `hist` file. Since this poll() returns POLLIN, the next
poll() will return soon unless a read() happens on that hist file.

NOTE: To read the hist file again, you must set the file offset to 0,
but just for monitoring the event, you may not need to read the
histogram.

Cc: Shuah Khan 
Cc: Mathieu Desnoyers 
Link: https://lore.kernel.org/173527247756.464571.14236296701625509931.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) 
Reviewed-by: Tom Zanussi 
Signed-off-by: Steven Rostedt (Google) 
Stable-dep-of: 0b4ffbe4888a ("tracing: Correct the refcount if the hist/hist_debug file fails to open")
Signed-off-by: Sasha Levin

tracing: Switch trace_events_hist.c code over to use guard()

2025-04-10T12:39:35+00:00

[ Upstream commit 2b36a97aeeb71b1e4a48bfedc7f21f44aeb1e6fb ]

There are a couple functions in trace_events_hist.c that have "goto out" or
equivalent on error in order to release locks that were taken. This can be
error prone or just simply make the code more complex.

Switch every location that ends with unlocking a mutex on error over to
using the guard(mutex)() infrastructure to let the compiler worry about
releasing locks. This makes the code easier to read and understand.

Cc: Masami Hiramatsu 
Cc: Mark Rutland 
Cc: Mathieu Desnoyers 
Cc: Andrew Morton 
Cc: Peter Zijlstra 
Link: https://lore.kernel.org/20241219201345.694601480@goodmis.org
Signed-off-by: Steven Rostedt (Google) 
Stable-dep-of: 0b4ffbe4888a ("tracing: Correct the refcount if the hist/hist_debug file fails to open")
Signed-off-by: Sasha Levin