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[ Upstream commit 8a96c0288d0737ad77882024974c075345c72011 ]
When ring_buffer_swap_cpu was called during resize process,
the cpu buffer was swapped in the middle, resulting in incorrect state.
Continuing to run in the wrong state will result in oops.
This issue can be easily reproduced using the following two scripts:
/tmp # cat test1.sh
//#! /bin/sh
for i in `seq 0 100000`
do
echo 2000 > /sys/kernel/debug/tracing/buffer_size_kb
sleep 0.5
echo 5000 > /sys/kernel/debug/tracing/buffer_size_kb
sleep 0.5
done
/tmp # cat test2.sh
//#! /bin/sh
for i in `seq 0 100000`
do
echo irqsoff > /sys/kernel/debug/tracing/current_tracer
sleep 1
echo nop > /sys/kernel/debug/tracing/current_tracer
sleep 1
done
/tmp # ./test1.sh &
/tmp # ./test2.sh &
A typical oops log is as follows, sometimes with other different oops logs.
[ 231.711293] WARNING: CPU: 0 PID: 9 at kernel/trace/ring_buffer.c:2026 rb_update_pages+0x378/0x3f8
[ 231.713375] Modules linked in:
[ 231.714735] CPU: 0 PID: 9 Comm: kworker/0:1 Tainted: G W 6.5.0-rc1-00276-g20edcec23f92 #15
[ 231.716750] Hardware name: linux,dummy-virt (DT)
[ 231.718152] Workqueue: events update_pages_handler
[ 231.719714] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 231.721171] pc : rb_update_pages+0x378/0x3f8
[ 231.722212] lr : rb_update_pages+0x25c/0x3f8
[ 231.723248] sp : ffff800082b9bd50
[ 231.724169] x29: ffff800082b9bd50 x28: ffff8000825f7000 x27: 0000000000000000
[ 231.726102] x26: 0000000000000001 x25: fffffffffffff010 x24: 0000000000000ff0
[ 231.728122] x23: ffff0000c3a0b600 x22: ffff0000c3a0b5c0 x21: fffffffffffffe0a
[ 231.730203] x20: ffff0000c3a0b600 x19: ffff0000c0102400 x18: 0000000000000000
[ 231.732329] x17: 0000000000000000 x16: 0000000000000000 x15: 0000ffffe7aa8510
[ 231.734212] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000002
[ 231.736291] x11: ffff8000826998a8 x10: ffff800082b9baf0 x9 : ffff800081137558
[ 231.738195] x8 : fffffc00030e82c8 x7 : 0000000000000000 x6 : 0000000000000001
[ 231.740192] x5 : ffff0000ffbafe00 x4 : 0000000000000000 x3 : 0000000000000000
[ 231.742118] x2 : 00000000000006aa x1 : 0000000000000001 x0 : ffff0000c0007208
[ 231.744196] Call trace:
[ 231.744892] rb_update_pages+0x378/0x3f8
[ 231.745893] update_pages_handler+0x1c/0x38
[ 231.746893] process_one_work+0x1f0/0x468
[ 231.747852] worker_thread+0x54/0x410
[ 231.748737] kthread+0x124/0x138
[ 231.749549] ret_from_fork+0x10/0x20
[ 231.750434] ---[ end trace 0000000000000000 ]---
[ 233.720486] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[ 233.721696] Mem abort info:
[ 233.721935] ESR = 0x0000000096000004
[ 233.722283] EC = 0x25: DABT (current EL), IL = 32 bits
[ 233.722596] SET = 0, FnV = 0
[ 233.722805] EA = 0, S1PTW = 0
[ 233.723026] FSC = 0x04: level 0 translation fault
[ 233.723458] Data abort info:
[ 233.723734] ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
[ 233.724176] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 233.724589] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 233.725075] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000104943000
[ 233.725592] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
[ 233.726231] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
[ 233.726720] Modules linked in:
[ 233.727007] CPU: 0 PID: 9 Comm: kworker/0:1 Tainted: G W 6.5.0-rc1-00276-g20edcec23f92 #15
[ 233.727777] Hardware name: linux,dummy-virt (DT)
[ 233.728225] Workqueue: events update_pages_handler
[ 233.728655] pstate: 200000c5 (nzCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 233.729054] pc : rb_update_pages+0x1a8/0x3f8
[ 233.729334] lr : rb_update_pages+0x154/0x3f8
[ 233.729592] sp : ffff800082b9bd50
[ 233.729792] x29: ffff800082b9bd50 x28: ffff8000825f7000 x27: 0000000000000000
[ 233.730220] x26: 0000000000000000 x25: ffff800082a8b840 x24: ffff0000c0102418
[ 233.730653] x23: 0000000000000000 x22: fffffc000304c880 x21: 0000000000000003
[ 233.731105] x20: 00000000000001f4 x19: ffff0000c0102400 x18: ffff800082fcbc58
[ 233.731727] x17: 0000000000000000 x16: 0000000000000001 x15: 0000000000000001
[ 233.732282] x14: ffff8000825fe0c8 x13: 0000000000000001 x12: 0000000000000000
[ 233.732709] x11: ffff8000826998a8 x10: 0000000000000ae0 x9 : ffff8000801b760c
[ 233.733148] x8 : fefefefefefefeff x7 : 0000000000000018 x6 : ffff0000c03298c0
[ 233.733553] x5 : 0000000000000002 x4 : 0000000000000000 x3 : 0000000000000000
[ 233.733972] x2 : ffff0000c3a0b600 x1 : 0000000000000000 x0 : 0000000000000000
[ 233.734418] Call trace:
[ 233.734593] rb_update_pages+0x1a8/0x3f8
[ 233.734853] update_pages_handler+0x1c/0x38
[ 233.735148] process_one_work+0x1f0/0x468
[ 233.735525] worker_thread+0x54/0x410
[ 233.735852] kthread+0x124/0x138
[ 233.736064] ret_from_fork+0x10/0x20
[ 233.736387] Code: 92400000 910006b5 aa000021 aa0303f7 (f9400060)
[ 233.736959] ---[ end trace 0000000000000000 ]---
After analysis, the seq of the error is as follows [1-5]:
int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size,
int cpu_id)
{
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
//1. get cpu_buffer, aka cpu_buffer(A)
...
...
schedule_work_on(cpu,
&cpu_buffer->update_pages_work);
//2. 'update_pages_work' is queue on 'cpu', cpu_buffer(A) is passed to
// update_pages_handler, do the update process, set 'update_done' in
// complete(&cpu_buffer->update_done) and to wakeup resize process.
//---->
//3. Just at this moment, ring_buffer_swap_cpu is triggered,
//cpu_buffer(A) be swaped to cpu_buffer(B), the max_buffer.
//ring_buffer_swap_cpu is called as the 'Call trace' below.
Call trace:
dump_backtrace+0x0/0x2f8
show_stack+0x18/0x28
dump_stack+0x12c/0x188
ring_buffer_swap_cpu+0x2f8/0x328
update_max_tr_single+0x180/0x210
check_critical_timing+0x2b4/0x2c8
tracer_hardirqs_on+0x1c0/0x200
trace_hardirqs_on+0xec/0x378
el0_svc_common+0x64/0x260
do_el0_svc+0x90/0xf8
el0_svc+0x20/0x30
el0_sync_handler+0xb0/0xb8
el0_sync+0x180/0x1c0
//<----
/* wait for all the updates to complete */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
//4. get cpu_buffer, cpu_buffer(B) is used in the following process,
//the state of cpu_buffer(A) and cpu_buffer(B) is totally wrong.
//for example, cpu_buffer(A)->update_done will leave be set 1, and will
//not 'wait_for_completion' at the next resize round.
if (!cpu_buffer->nr_pages_to_update)
continue;
if (cpu_online(cpu))
wait_for_completion(&cpu_buffer->update_done);
cpu_buffer->nr_pages_to_update = 0;
}
...
}
//5. the state of cpu_buffer(A) and cpu_buffer(B) is totally wrong,
//Continuing to run in the wrong state, then oops occurs.
Link: https://lore.kernel.org/linux-trace-kernel/202307191558478409990@zte.com.cn
Signed-off-by: Chen Lin <chen.lin5@zte.com.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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[ Upstream commit 2d093282b0d4357373497f65db6a05eb0c28b7c8 ]
When pages are removed in rb_remove_pages(), 'cpu_buffer->read' is set
to 0 in order to make sure any read iterators reset themselves. However,
this will mess 'entries' stating, see following steps:
# cd /sys/kernel/tracing/
# 1. Enlarge ring buffer prepare for later reducing:
# echo 20 > per_cpu/cpu0/buffer_size_kb
# 2. Write a log into ring buffer of cpu0:
# taskset -c 0 echo "hello1" > trace_marker
# 3. Read the log:
# cat per_cpu/cpu0/trace_pipe
<...>-332 [000] ..... 62.406844: tracing_mark_write: hello1
# 4. Stop reading and see the stats, now 0 entries, and 1 event readed:
# cat per_cpu/cpu0/stats
entries: 0
[...]
read events: 1
# 5. Reduce the ring buffer
# echo 7 > per_cpu/cpu0/buffer_size_kb
# 6. Now entries became unexpected 1 because actually no entries!!!
# cat per_cpu/cpu0/stats
entries: 1
[...]
read events: 0
To fix it, introduce 'page_removed' field to count total removed pages
since last reset, then use it to let read iterators reset themselves
instead of changing the 'read' pointer.
Link: https://lore.kernel.org/linux-trace-kernel/20230724054040.3489499-1-zhengyejian1@huawei.com
Cc: <mhiramat@kernel.org>
Cc: <vnagarnaik@google.com>
Fixes: 83f40318dab0 ("ring-buffer: Make removal of ring buffer pages atomic")
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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commit 7e42907f3a7b4ce3a2d1757f6d78336984daf8f5 upstream.
Soft lockup occurs when reading file 'trace_pipe':
watchdog: BUG: soft lockup - CPU#6 stuck for 22s! [cat:4488]
[...]
RIP: 0010:ring_buffer_empty_cpu+0xed/0x170
RSP: 0018:ffff88810dd6fc48 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000246 RCX: ffffffff93d1aaeb
RDX: ffff88810a280040 RSI: 0000000000000008 RDI: ffff88811164b218
RBP: ffff88811164b218 R08: 0000000000000000 R09: ffff88815156600f
R10: ffffed102a2acc01 R11: 0000000000000001 R12: 0000000051651901
R13: 0000000000000000 R14: ffff888115e49500 R15: 0000000000000000
[...]
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8d853c2000 CR3: 000000010dcd8000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__find_next_entry+0x1a8/0x4b0
? peek_next_entry+0x250/0x250
? down_write+0xa5/0x120
? down_write_killable+0x130/0x130
trace_find_next_entry_inc+0x3b/0x1d0
tracing_read_pipe+0x423/0xae0
? tracing_splice_read_pipe+0xcb0/0xcb0
vfs_read+0x16b/0x490
ksys_read+0x105/0x210
? __ia32_sys_pwrite64+0x200/0x200
? switch_fpu_return+0x108/0x220
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x61/0xc6
Through the vmcore, I found it's because in tracing_read_pipe(),
ring_buffer_empty_cpu() found some buffer is not empty but then it
cannot read anything due to "rb_num_of_entries() == 0" always true,
Then it infinitely loop the procedure due to user buffer not been
filled, see following code path:
tracing_read_pipe() {
... ...
waitagain:
tracing_wait_pipe() // 1. find non-empty buffer here
trace_find_next_entry_inc() // 2. loop here try to find an entry
__find_next_entry()
ring_buffer_empty_cpu(); // 3. find non-empty buffer
peek_next_entry() // 4. but peek always return NULL
ring_buffer_peek()
rb_buffer_peek()
rb_get_reader_page()
// 5. because rb_num_of_entries() == 0 always true here
// then return NULL
// 6. user buffer not been filled so goto 'waitgain'
// and eventually leads to an deadloop in kernel!!!
}
By some analyzing, I found that when resetting ringbuffer, the 'entries'
of its pages are not all cleared (see rb_reset_cpu()). Then when reducing
the ringbuffer, and if some reduced pages exist dirty 'entries' data, they
will be added into 'cpu_buffer->overrun' (see rb_remove_pages()), which
cause wrong 'overrun' count and eventually cause the deadloop issue.
To fix it, we need to clear every pages in rb_reset_cpu().
Link: https://lore.kernel.org/linux-trace-kernel/20230708225144.3785600-1-zhengyejian1@huawei.com
Cc: stable@vger.kernel.org
Fixes: a5fb833172eca ("ring-buffer: Fix uninitialized read_stamp")
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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ring_buffer_reset_online_cpus
[ Upstream commit 7c339fb4d8577792378136c15fde773cfb863cb8 ]
In ring_buffer_reset_online_cpus, the buffer_size_kb write operation
may permanently fail if the cpu_online_mask changes between two
for_each_online_buffer_cpu loops. The number of increases and decreases
on both cpu_buffer->resize_disabled and cpu_buffer->record_disabled may be
inconsistent, causing some CPUs to have non-zero values for these atomic
variables after the function returns.
This issue can be reproduced by "echo 0 > trace" while hotplugging cpu.
After reproducing success, we can find out buffer_size_kb will not be
functional anymore.
To prevent leaving 'resize_disabled' and 'record_disabled' non-zero after
ring_buffer_reset_online_cpus returns, we ensure that each atomic variable
has been set up before atomic_sub() to it.
Link: https://lore.kernel.org/linux-trace-kernel/20230426062027.17451-1-Tze-nan.Wu@mediatek.com
Cc: stable@vger.kernel.org
Cc: <mhiramat@kernel.org>
Cc: npiggin@gmail.com
Fixes: b23d7a5f4a07 ("ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU")
Reviewed-by: Cheng-Jui Wang <cheng-jui.wang@mediatek.com>
Signed-off-by: Tze-nan Wu <Tze-nan.Wu@mediatek.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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commit 675751bb20634f981498c7d66161584080cc061e upstream.
If something was written to the buffer just before destruction,
it may be possible (maybe not in a real system, but it did
happen in ARCH=um with time-travel) to destroy the ringbuffer
before the IRQ work ran, leading this KASAN report (or a crash
without KASAN):
BUG: KASAN: slab-use-after-free in irq_work_run_list+0x11a/0x13a
Read of size 8 at addr 000000006d640a48 by task swapper/0
CPU: 0 PID: 0 Comm: swapper Tainted: G W O 6.3.0-rc1 #7
Stack:
60c4f20f 0c203d48 41b58ab3 60f224fc
600477fa 60f35687 60c4f20f 601273dd
00000008 6101eb00 6101eab0 615be548
Call Trace:
[<60047a58>] show_stack+0x25e/0x282
[<60c609e0>] dump_stack_lvl+0x96/0xfd
[<60c50d4c>] print_report+0x1a7/0x5a8
[<603078d3>] kasan_report+0xc1/0xe9
[<60308950>] __asan_report_load8_noabort+0x1b/0x1d
[<60232844>] irq_work_run_list+0x11a/0x13a
[<602328b4>] irq_work_tick+0x24/0x34
[<6017f9dc>] update_process_times+0x162/0x196
[<6019f335>] tick_sched_handle+0x1a4/0x1c3
[<6019fd9e>] tick_sched_timer+0x79/0x10c
[<601812b9>] __hrtimer_run_queues.constprop.0+0x425/0x695
[<60182913>] hrtimer_interrupt+0x16c/0x2c4
[<600486a3>] um_timer+0x164/0x183
[...]
Allocated by task 411:
save_stack_trace+0x99/0xb5
stack_trace_save+0x81/0x9b
kasan_save_stack+0x2d/0x54
kasan_set_track+0x34/0x3e
kasan_save_alloc_info+0x25/0x28
____kasan_kmalloc+0x8b/0x97
__kasan_kmalloc+0x10/0x12
__kmalloc+0xb2/0xe8
load_elf_phdrs+0xee/0x182
[...]
The buggy address belongs to the object at 000000006d640800
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 584 bytes inside of
freed 1024-byte region [000000006d640800, 000000006d640c00)
Add the appropriate irq_work_sync() so the work finishes before
the buffers are destroyed.
Prior to the commit in the Fixes tag below, there was only a
single global IRQ work, so this issue didn't exist.
Link: https://lore.kernel.org/linux-trace-kernel/20230427175920.a76159263122.I8295e405c44362a86c995e9c2c37e3e03810aa56@changeid
Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 15693458c4bc ("tracing/ring-buffer: Move poll wake ups into ring buffer code")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit 6455b6163d8c680366663cdb8c679514d55fc30c upstream.
When user reads file 'trace_pipe', kernel keeps printing following logs
that warn at "cpu_buffer->reader_page->read > rb_page_size(reader)" in
rb_get_reader_page(). It just looks like there's an infinite loop in
tracing_read_pipe(). This problem occurs several times on arm64 platform
when testing v5.10 and below.
Call trace:
rb_get_reader_page+0x248/0x1300
rb_buffer_peek+0x34/0x160
ring_buffer_peek+0xbc/0x224
peek_next_entry+0x98/0xbc
__find_next_entry+0xc4/0x1c0
trace_find_next_entry_inc+0x30/0x94
tracing_read_pipe+0x198/0x304
vfs_read+0xb4/0x1e0
ksys_read+0x74/0x100
__arm64_sys_read+0x24/0x30
el0_svc_common.constprop.0+0x7c/0x1bc
do_el0_svc+0x2c/0x94
el0_svc+0x20/0x30
el0_sync_handler+0xb0/0xb4
el0_sync+0x160/0x180
Then I dump the vmcore and look into the problematic per_cpu ring_buffer,
I found that tail_page/commit_page/reader_page are on the same page while
reader_page->read is obviously abnormal:
tail_page == commit_page == reader_page == {
.write = 0x100d20,
.read = 0x8f9f4805, // Far greater than 0xd20, obviously abnormal!!!
.entries = 0x10004c,
.real_end = 0x0,
.page = {
.time_stamp = 0x857257416af0,
.commit = 0xd20, // This page hasn't been full filled.
// .data[0...0xd20] seems normal.
}
}
The root cause is most likely the race that reader and writer are on the
same page while reader saw an event that not fully committed by writer.
To fix this, add memory barriers to make sure the reader can see the
content of what is committed. Since commit a0fcaaed0c46 ("ring-buffer: Fix
race between reset page and reading page") has added the read barrier in
rb_get_reader_page(), here we just need to add the write barrier.
Link: https://lore.kernel.org/linux-trace-kernel/20230325021247.2923907-1-zhengyejian1@huawei.com
Cc: stable@vger.kernel.org
Fixes: 77ae365eca89 ("ring-buffer: make lockless")
Suggested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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[ Upstream commit 3e4272b9954094907f16861199728f14002fcaf6 ]
In a previous commit 7433632c9ff6, buffer, buffer->buffers and
buffer->buffers[cpu] in ring_buffer_wake_waiters() can be NULL,
and thus the related checks are added.
However, in the same call stack, these variables are also used in
ring_buffer_free_read_page():
tracing_buffers_release()
ring_buffer_wake_waiters(iter->array_buffer->buffer)
cpu_buffer = buffer->buffers[cpu] -> Add checks by previous commit
ring_buffer_free_read_page(iter->array_buffer->buffer)
cpu_buffer = buffer->buffers[cpu] -> No check
Thus, to avod possible null-pointer derefernces, the related checks
should be added.
These results are reported by a static tool designed by myself.
Link: https://lkml.kernel.org/r/20230113125501.760324-1-baijiaju1990@gmail.com
Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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commit 8843e06f67b14f71c044bf6267b2387784c7e198 upstream.
It seems a data race between ring_buffer writing and integrity check.
That is, RB_FLAG of head_page is been updating, while at same time
RB_FLAG was cleared when doing integrity check rb_check_pages():
rb_check_pages() rb_handle_head_page():
-------- --------
rb_head_page_deactivate()
rb_head_page_set_normal()
rb_head_page_activate()
We do intergrity test of the list to check if the list is corrupted and
it is still worth doing it. So, let's refactor rb_check_pages() such that
we no longer clear and set flag during the list sanity checking.
[1] and [2] are the test to reproduce and the crash report respectively.
1:
``` read_trace.sh
while true;
do
# the "trace" file is closed after read
head -1 /sys/kernel/tracing/trace > /dev/null
done
```
``` repro.sh
sysctl -w kernel.panic_on_warn=1
# function tracer will writing enough data into ring_buffer
echo function > /sys/kernel/tracing/current_tracer
./read_trace.sh &
./read_trace.sh &
./read_trace.sh &
./read_trace.sh &
./read_trace.sh &
./read_trace.sh &
./read_trace.sh &
./read_trace.sh &
```
2:
------------[ cut here ]------------
WARNING: CPU: 9 PID: 62 at kernel/trace/ring_buffer.c:2653
rb_move_tail+0x450/0x470
Modules linked in:
CPU: 9 PID: 62 Comm: ksoftirqd/9 Tainted: G W 6.2.0-rc6+
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
RIP: 0010:rb_move_tail+0x450/0x470
Code: ff ff 4c 89 c8 f0 4d 0f b1 02 48 89 c2 48 83 e2 fc 49 39 d0 75 24
83 e0 03 83 f8 02 0f 84 e1 fb ff ff 48 8b 57 10 f0 ff 42 08 <0f> 0b 83
f8 02 0f 84 ce fb ff ff e9 db
RSP: 0018:ffffb5564089bd00 EFLAGS: 00000203
RAX: 0000000000000000 RBX: ffff9db385a2bf81 RCX: ffffb5564089bd18
RDX: ffff9db281110100 RSI: 0000000000000fe4 RDI: ffff9db380145400
RBP: ffff9db385a2bf80 R08: ffff9db385a2bfc0 R09: ffff9db385a2bfc2
R10: ffff9db385a6c000 R11: ffff9db385a2bf80 R12: 0000000000000000
R13: 00000000000003e8 R14: ffff9db281110100 R15: ffffffffbb006108
FS: 0000000000000000(0000) GS:ffff9db3bdcc0000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005602323024c8 CR3: 0000000022e0c000 CR4: 00000000000006e0
Call Trace:
<TASK>
ring_buffer_lock_reserve+0x136/0x360
? __do_softirq+0x287/0x2df
? __pfx_rcu_softirq_qs+0x10/0x10
trace_function+0x21/0x110
? __pfx_rcu_softirq_qs+0x10/0x10
? __do_softirq+0x287/0x2df
function_trace_call+0xf6/0x120
0xffffffffc038f097
? rcu_softirq_qs+0x5/0x140
rcu_softirq_qs+0x5/0x140
__do_softirq+0x287/0x2df
run_ksoftirqd+0x2a/0x30
smpboot_thread_fn+0x188/0x220
? __pfx_smpboot_thread_fn+0x10/0x10
kthread+0xe7/0x110
? __pfx_kthread+0x10/0x10
ret_from_fork+0x2c/0x50
</TASK>
---[ end trace 0000000000000000 ]---
[ crash report and test reproducer credit goes to Zheng Yejian]
Link: https://lore.kernel.org/linux-trace-kernel/1676376403-16462-1-git-send-email-quic_mojha@quicinc.com
Cc: <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Fixes: 1039221cc278 ("ring-buffer: Do not disable recording when there is an iterator")
Reported-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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[ Upstream commit 31029a8b2c7e656a0289194ef16415050ae4c4ac ]
The function ring_buffer_nr_dirty_pages() was created to find out how many
pages are filled in the ring buffer. There's two running counters. One is
incremented whenever a new page is touched (pages_touched) and the other
is whenever a page is read (pages_read). The dirty count is the number
touched minus the number read. This is used to determine if a blocked task
should be woken up if the percentage of the ring buffer it is waiting for
is hit.
The problem is that it does not take into account dropped pages (when the
new writes overwrite pages that were not read). And then the dirty pages
will always be greater than the percentage.
This makes the "buffer_percent" file inaccurate, as the number of dirty
pages end up always being larger than the percentage, event when it's not
and this causes user space to be woken up more than it wants to be.
Add a new counter to keep track of lost pages, and include that in the
accounting of dirty pages so that it is actually accurate.
Link: https://lkml.kernel.org/r/20221021123013.55fb6055@gandalf.local.home
Fixes: 2c2b0a78b3739 ("ring-buffer: Add percentage of ring buffer full to wake up reader")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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commit 42fb0a1e84ff525ebe560e2baf9451ab69127e2b upstream.
Currently the way polling works on the ring buffer is broken. It will
return immediately if there's any data in the ring buffer whereas a read
will block until the watermark (defined by the tracefs buffer_percent file)
is hit.
That is, a select() or poll() will return as if there's data available,
but then the following read will block. This is broken for the way
select()s and poll()s are supposed to work.
Have the polling on the ring buffer also block the same way reads and
splice does on the ring buffer.
Link: https://lkml.kernel.org/r/20221020231427.41be3f26@gandalf.local.home
Cc: Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Primiano Tucci <primiano@google.com>
Cc: stable@vger.kernel.org
Fixes: 1e0d6714aceb7 ("ring-buffer: Do not wake up a splice waiter when page is not full")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit 56f4ca0a79a9f1af98f26c54b9b89ba1f9bcc6bd upstream.
rb_head_page_deactivate() expects cpu_buffer to contain a valid list of
->pages, so verify that the list is actually present before calling it.
Found by Linux Verification Center (linuxtesting.org) with the SVACE
static analysis tool.
Link: https://lkml.kernel.org/r/20221114143129.3534443-1-d-tatianin@yandex-team.ru
Cc: stable@vger.kernel.org
Fixes: 77ae365eca895 ("ring-buffer: make lockless")
Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit a0fcaaed0c46cf9399d3a2d6e0c87ddb3df0e044 upstream.
The ring buffer is broken up into sub buffers (currently of page size).
Each sub buffer has a pointer to its "tail" (the last event written to the
sub buffer). When a new event is requested, the tail is locally
incremented to cover the size of the new event. This is done in a way that
there is no need for locking.
If the tail goes past the end of the sub buffer, the process of moving to
the next sub buffer takes place. After setting the current sub buffer to
the next one, the previous one that had the tail go passed the end of the
sub buffer needs to be reset back to the original tail location (before
the new event was requested) and the rest of the sub buffer needs to be
"padded".
The race happens when a reader takes control of the sub buffer. As readers
do a "swap" of sub buffers from the ring buffer to get exclusive access to
the sub buffer, it replaces the "head" sub buffer with an empty sub buffer
that goes back into the writable portion of the ring buffer. This swap can
happen as soon as the writer moves to the next sub buffer and before it
updates the last sub buffer with padding.
Because the sub buffer can be released to the reader while the writer is
still updating the padding, it is possible for the reader to see the event
that goes past the end of the sub buffer. This can cause obvious issues.
To fix this, add a few memory barriers so that the reader definitely sees
the updates to the sub buffer, and also waits until the writer has put
back the "tail" of the sub buffer back to the last event that was written
on it.
To be paranoid, it will only spin for 1 second, otherwise it will
warn and shutdown the ring buffer code. 1 second should be enough as
the writer does have preemption disabled. If the writer doesn't move
within 1 second (with preemption disabled) something is horribly
wrong. No interrupt should last 1 second!
Link: https://lore.kernel.org/all/20220830120854.7545-1-jiazi.li@transsion.com/
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216369
Link: https://lkml.kernel.org/r/20220929104909.0650a36c@gandalf.local.home
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org
Fixes: c7b0930857e22 ("ring-buffer: prevent adding write in discarded area")
Reported-by: Jiazi.Li <jiazi.li@transsion.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit 7e9fbbb1b776d8d7969551565bc246f74ec53b27 upstream.
On closing of a file that represents a ring buffer or flushing the file,
there may be waiters on the ring buffer that needs to be woken up and exit
the ring_buffer_wait() function.
Add ring_buffer_wake_waiters() to wake up the waiters on the ring buffer
and allow them to exit the wait loop.
Link: https://lkml.kernel.org/r/20220928133938.28dc2c27@gandalf.local.home
Cc: stable@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Fixes: 15693458c4bc0 ("tracing/ring-buffer: Move poll wake ups into ring buffer code")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit ec0bbc5ec5664dcee344f79373852117dc672c86 upstream.
The wake up waiters only checks the "wakeup_full" variable and not the
"full_waiters_pending". The full_waiters_pending is set when a waiter is
added to the wait queue. The wakeup_full is only set when an event is
triggered, and it clears the full_waiters_pending to avoid multiple calls
to irq_work_queue().
The irq_work callback really needs to check both wakeup_full as well as
full_waiters_pending such that this code can be used to wake up waiters
when a file is closed that represents the ring buffer and the waiters need
to be woken up.
Link: https://lkml.kernel.org/r/20220927231824.209460321@goodmis.org
Cc: stable@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Fixes: 15693458c4bc0 ("tracing/ring-buffer: Move poll wake ups into ring buffer code")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit 3b19d614b61b93a131f463817e08219c9ce1fee3 upstream.
The logic to know when the shortest waiters on the ring buffer should be
woken up or not has uses a less than instead of a greater than compare,
which causes the shortest_full to actually be the longest.
Link: https://lkml.kernel.org/r/20220927231823.718039222@goodmis.org
Cc: stable@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Fixes: 2c2b0a78b3739 ("ring-buffer: Add percentage of ring buffer full to wake up reader")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit fa8f4a89736b654125fb254b0db753ac68a5fced upstream.
If a page is partially read, and then the splice system call is run
against the ring buffer, it will always fail to read, no matter how much
is in the ring buffer. That's because the code path for a partial read of
the page does will fail if the "full" flag is set.
The splice system call wants full pages, so if the read of the ring buffer
is not yet full, it should return zero, and the splice will block. But if
a previous read was done, where the beginning has been consumed, it should
still be given to the splice caller if the rest of the page has been
written to.
This caused the splice command to never consume data in this scenario, and
let the ring buffer just fill up and lose events.
Link: https://lkml.kernel.org/r/20220927144317.46be6b80@gandalf.local.home
Cc: stable@vger.kernel.org
Fixes: 8789a9e7df6bf ("ring-buffer: read page interface")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit 51d157946666382e779f94c39891e8e9a020da78 upstream.
The resetting of the entire ring buffer use to simply go through and reset
each individual CPU buffer that had its own protection and synchronization.
But this was very slow, due to performing a synchronization for each CPU.
The code was reshuffled to do one disabling of all CPU buffers, followed
by a single RCU synchronization, and then the resetting of each of the CPU
buffers. But unfortunately, the mutex that prevented multiple occurrences
of resetting the buffer was not moved to the upper function, and there is
nothing to protect from it.
Take the ring buffer mutex around the global reset.
Cc: stable@vger.kernel.org
Fixes: b23d7a5f4a07a ("ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU")
Reported-by: "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit 67f0d6d9883c13174669f88adac4f0ee656cc16a upstream.
The "rb_per_cpu_empty()" misinterpret the condition (as not-empty) when
"head_page" and "commit_page" of "struct ring_buffer_per_cpu" points to
the same buffer page, whose "buffer_data_page" is empty and "read" field
is non-zero.
An error scenario could be constructed as followed (kernel perspective):
1. All pages in the buffer has been accessed by reader(s) so that all of
them will have non-zero "read" field.
2. Read and clear all buffer pages so that "rb_num_of_entries()" will
return 0 rendering there's no more data to read. It is also required
that the "read_page", "commit_page" and "tail_page" points to the same
page, while "head_page" is the next page of them.
3. Invoke "ring_buffer_lock_reserve()" with large enough "length"
so that it shot pass the end of current tail buffer page. Now the
"head_page", "commit_page" and "tail_page" points to the same page.
4. Discard current event with "ring_buffer_discard_commit()", so that
"head_page", "commit_page" and "tail_page" points to a page whose buffer
data page is now empty.
When the error scenario has been constructed, "tracing_read_pipe" will
be trapped inside a deadloop: "trace_empty()" returns 0 since
"rb_per_cpu_empty()" returns 0 when it hits the CPU containing such
constructed ring buffer. Then "trace_find_next_entry_inc()" always
return NULL since "rb_num_of_entries()" reports there's no more entry
to read. Finally "trace_seq_to_user()" returns "-EBUSY" spanking
"tracing_read_pipe" back to the start of the "waitagain" loop.
I've also written a proof-of-concept script to construct the scenario
and trigger the bug automatically, you can use it to trace and validate
my reasoning above:
https://github.com/aegistudio/RingBufferDetonator.git
Tests has been carried out on linux kernel 5.14-rc2
(2734d6c1b1a089fb593ef6a23d4b70903526fe0c), my fixed version
of kernel (for testing whether my update fixes the bug) and
some older kernels (for range of affected kernels). Test result is
also attached to the proof-of-concept repository.
Link: https://lore.kernel.org/linux-trace-devel/YPaNxsIlb2yjSi5Y@aegistudio/
Link: https://lore.kernel.org/linux-trace-devel/YPgrN85WL9VyrZ55@aegistudio
Cc: stable@vger.kernel.org
Fixes: bf41a158cacba ("ring-buffer: make reentrant")
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Haoran Luo <www@aegistudio.net>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit 6f6be606e763f2da9fc21de00538c97fe4ca1492 upstream.
Part of the logic of the new time stamp code depends on the before_stamp and
the write_stamp to be different if the write_stamp does not match the last
event on the buffer, as it will be used to calculate the delta of the next
event written on the buffer.
The discard logic depends on this, as the next event to come in needs to
inject a full timestamp as it can not rely on the last event timestamp in
the buffer because it is unknown due to events after it being discarded. But
by changing the write_stamp back to the time before it, it forces the next
event to use a full time stamp, instead of relying on it.
The issue came when a full time stamp was used for the event, and
rb_time_delta() returns zero in that case. The update to the write_stamp
(which subtracts delta) made it not change. Then when the event is removed
from the buffer, because the before_stamp and write_stamp still match, the
next event written would calculate its delta from the write_stamp, but that
would be wrong as the write_stamp is of the time of the event that was
discarded.
In the case that the delta change being made to write_stamp is zero, set the
before_stamp to zero as well, and this will force the next event to inject a
full timestamp and not use the current write_stamp.
Cc: stable@vger.kernel.org
Fixes: a389d86f7fd09 ("ring-buffer: Have nested events still record running time stamp")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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commit adab66b71abfe206a020f11e561f4df41f0b2aba upstream.
It was believed that metag was the only architecture that required the ring
buffer to keep 8 byte words aligned on 8 byte architectures, and with its
removal, it was assumed that the ring buffer code did not need to handle
this case. It appears that sparc64 also requires this.
The following was reported on a sparc64 boot up:
kernel: futex hash table entries: 65536 (order: 9, 4194304 bytes, linear)
kernel: Running postponed tracer tests:
kernel: Testing tracer function:
kernel: Kernel unaligned access at TPC[552a20] trace_function+0x40/0x140
kernel: Kernel unaligned access at TPC[552a24] trace_function+0x44/0x140
kernel: Kernel unaligned access at TPC[552a20] trace_function+0x40/0x140
kernel: Kernel unaligned access at TPC[552a24] trace_function+0x44/0x140
kernel: Kernel unaligned access at TPC[552a20] trace_function+0x40/0x140
kernel: PASSED
Need to put back the 64BIT aligned code for the ring buffer.
Link: https://lore.kernel.org/r/CADxRZqzXQRYgKc=y-KV=S_yHL+Y8Ay2mh5ezeZUnpRvg+syWKw@mail.gmail.com
Cc: stable@vger.kernel.org
Fixes: 86b3de60a0b6 ("ring-buffer: Remove HAVE_64BIT_ALIGNED_ACCESS")
Reported-by: Anatoly Pugachev <matorola@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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The current ring buffer logic checks to see if the updating of the event
buffer was interrupted, and if it is, it will try to fix up the before stamp
with the write stamp to make them equal again. This logic is flawed, because
if it is not interrupted, the two are guaranteed to be different, as the
current event just updated the before stamp before allocation. This
guarantees that the next event (this one or another interrupting one) will
think it interrupted the time updates of a previous event and inject an
absolute time stamp to compensate.
The correct logic is to always update the timestamps when traversing to a
new sub buffer.
Cc: stable@vger.kernel.org
Fixes: a389d86f7fd09 ("ring-buffer: Have nested events still record running time stamp")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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In the slow path of __rb_reserve_next() a nested event(s) can happen
between evaluating the timestamp delta of the current event and updating
write_stamp via local_cmpxchg(); in this case the delta is not valid
anymore and it should be set to 0 (same timestamp as the interrupting
event), since the event that we are currently processing is not the last
event in the buffer.
Link: https://lkml.kernel.org/r/X8IVJcp1gRE+FJCJ@xps-13-7390
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lwn.net/Articles/831207
Fixes: a389d86f7fd0 ("ring-buffer: Have nested events still record running time stamp")
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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The write stamp, used to calculate deltas between events, was updated with
the stale "ts" value in the "info" structure, and not with the updated "ts"
variable. This caused the deltas between events to be inaccurate, and when
crossing into a new sub buffer, had time go backwards.
Link: https://lkml.kernel.org/r/20201124223917.795844-1-elavila@google.com
Cc: stable@vger.kernel.org
Fixes: a389d86f7fd09 ("ring-buffer: Have nested events still record running time stamp")
Reported-by: "J. Avila" <elavila@google.com>
Tested-by: Daniel Mentz <danielmentz@google.com>
Tested-by: Will McVicker <willmcvicker@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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The recursion protection of the ring buffer depends on preempt_count() to be
correct. But it is possible that the ring buffer gets called after an
interrupt comes in but before it updates the preempt_count(). This will
trigger a false positive in the recursion code.
Use the same trick from the ftrace function callback recursion code which
uses a "transition" bit that gets set, to allow for a single recursion for
to handle transitions between contexts.
Cc: stable@vger.kernel.org
Fixes: 567cd4da54ff4 ("ring-buffer: User context bit recursion checking")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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The function changed at some point, but the description was not
updated.
Link: https://lkml.kernel.org/r/20201017095246.5170-1-hqjagain@gmail.com
Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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We don't need to check the new buffer size, and the return value
had confused resize_buffer_duplicate_size().
...
ret = ring_buffer_resize(trace_buf->buffer,
per_cpu_ptr(size_buf->data,cpu_id)->entries, cpu_id);
if (ret == 0)
per_cpu_ptr(trace_buf->data, cpu_id)->entries =
per_cpu_ptr(size_buf->data, cpu_id)->entries;
...
Link: https://lkml.kernel.org/r/20201019142242.11560-1-hqjagain@gmail.com
Cc: stable@vger.kernel.org
Fixes: d60da506cbeb3 ("tracing: Add a resize function to make one buffer equivalent to another buffer")
Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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Below race can come, if trace_open and resize of
cpu buffer is running parallely on different cpus
CPUX CPUY
ring_buffer_resize
atomic_read(&buffer->resize_disabled)
tracing_open
tracing_reset_online_cpus
ring_buffer_reset_cpu
rb_reset_cpu
rb_update_pages
remove/insert pages
resetting pointer
This race can cause data abort or some times infinte loop in
rb_remove_pages and rb_insert_pages while checking pages
for sanity.
Take buffer lock to fix this.
Link: https://lkml.kernel.org/r/1601976833-24377-1-git-send-email-gkohli@codeaurora.org
Cc: stable@vger.kernel.org
Fixes: b23d7a5f4a07a ("ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU")
Signed-off-by: Gaurav Kohli <gkohli@codeaurora.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull tracing updates from Steven Rostedt:
- The biggest news in that the tracing ring buffer can now time events
that interrupted other ring buffer events.
Before this change, if an interrupt came in while recording another
event, and that interrupt also had an event, those events would all
have the same time stamp as the event it interrupted.
Now, with the new design, those events will have a unique time stamp
and rightfully display the time for those events that were recorded
while interrupting another event.
- Bootconfig how has an "override" operator that lets the users have a
default config, but then add options to override the default.
- A fix was made to properly filter function graph tracing to the
ftrace PIDs. This came in at the end of the -rc cycle, and needs to
be backported.
- Several clean ups, performance updates, and minor fixes as well.
* tag 'trace-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (39 commits)
tracing: Add trace_array_init_printk() to initialize instance trace_printk() buffers
kprobes: Fix compiler warning for !CONFIG_KPROBES_ON_FTRACE
tracing: Use trace_sched_process_free() instead of exit() for pid tracing
bootconfig: Fix to find the initargs correctly
Documentation: bootconfig: Add bootconfig override operator
tools/bootconfig: Add testcases for value override operator
lib/bootconfig: Add override operator support
kprobes: Remove show_registers() function prototype
tracing/uprobe: Remove dead code in trace_uprobe_register()
kprobes: Fix NULL pointer dereference at kprobe_ftrace_handler
ftrace: Fix ftrace_trace_task return value
tracepoint: Use __used attribute definitions from compiler_attributes.h
tracepoint: Mark __tracepoint_string's __used
trace : Have tracing buffer info use kvzalloc instead of kzalloc
tracing: Remove outdated comment in stack handling
ftrace: Do not let direct or IPMODIFY ftrace_ops be added to module and set trampolines
ftrace: Setup correct FTRACE_FL_REGS flags for module
tracing/hwlat: Honor the tracing_cpumask
tracing/hwlat: Drop the duplicate assignment in start_kthread()
tracing: Save one trace_event->type by using __TRACE_LAST_TYPE
...
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Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings
(e.g. "unused variable"). If the compiler thinks it is uninitialized,
either simply initialize the variable or make compiler changes.
In preparation for removing[2] the[3] macro[4], remove all remaining
needless uses with the following script:
git grep '\buninitialized_var\b' | cut -d: -f1 | sort -u | \
xargs perl -pi -e \
's/\buninitialized_var\(([^\)]+)\)/\1/g;
s:\s*/\* (GCC be quiet|to make compiler happy) \*/$::g;'
drivers/video/fbdev/riva/riva_hw.c was manually tweaked to avoid
pathological white-space.
No outstanding warnings were found building allmodconfig with GCC 9.3.0
for x86_64, i386, arm64, arm, powerpc, powerpc64le, s390x, mips, spar |
