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ring-buffer: Ensure proper resetting of atomic variables in ring_buffer_reset_online_cpus

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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: b23d7a5f4a ("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>
This commit is contained in:
Tze-nan Wu 2023-04-26 14:20:23 +08:00 committed by Steven Rostedt (Google)
parent fa359d0685
commit 7c339fb4d8
1 changed files with 13 additions and 3 deletions
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16
kernel/trace/ring_buffer.c
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@ -5326,6 +5326,9 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
}
EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
/* Flag to ensure proper resetting of atomic variables */
#define RESET_BIT (1 << 30)
/**
* ring_buffer_reset_online_cpus - reset a ring buffer per CPU buffer
* @buffer: The ring buffer to reset a per cpu buffer of
@ -5342,20 +5345,27 @@ void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
for_each_online_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
atomic_inc(&cpu_buffer->resize_disabled);
atomic_add(RESET_BIT, &cpu_buffer->resize_disabled);
atomic_inc(&cpu_buffer->record_disabled);
}
/* Make sure all commits have finished */
synchronize_rcu();
for_each_online_buffer_cpu(buffer, cpu) {
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
/*
* If a CPU came online during the synchronize_rcu(), then
* ignore it.
*/
if (!(atomic_read(&cpu_buffer->resize_disabled) & RESET_BIT))
continue;
reset_disabled_cpu_buffer(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&cpu_buffer->resize_disabled);
atomic_sub(RESET_BIT, &cpu_buffer->resize_disabled);
}
mutex_unlock(&buffer->mutex);