This is a note to let you know that I've just added the patch titled
ring-buffer: Protect ring_buffer_reset() from reentrancy
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ring-buffer-protect-ring_buffer_reset-from-reentrancy.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 51d157946666382e779f94c39891e8e9a020da78 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
Date: Mon, 8 Nov 2021 10:58:10 -0500
Subject: ring-buffer: Protect ring_buffer_reset() from reentrancy
From: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
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@xxxxxxxxxxxxxxx
Fixes: b23d7a5f4a07a ("ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU")
Reported-by: "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@xxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/trace/ring_buffer.c | 5 +++++
1 file changed, 5 insertions(+)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -5233,6 +5233,9 @@ void ring_buffer_reset(struct trace_buff
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
+ /* prevent another thread from changing buffer sizes */
+ mutex_lock(&buffer->mutex);
+
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
@@ -5251,6 +5254,8 @@ void ring_buffer_reset(struct trace_buff
atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&cpu_buffer->resize_disabled);
}
+
+ mutex_unlock(&buffer->mutex);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset);
Patches currently in stable-queue which might be from rostedt@xxxxxxxxxxx are
queue-5.15/ia64-kprobes-fix-to-pass-correct-trampoline-address-to-the-handler.patch
queue-5.15/ring-buffer-protect-ring_buffer_reset-from-reentrancy.patch
