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From d8fb64e4164d3f4c89eb58c27b2472a052359823 Mon Sep 17 00:00:00 2001
From: Gaurav Kohli <gkohli@codeaurora.org>
Date: Tue, 6 Oct 2020 15:03:53 +0530
Subject: [PATCH] tracing: Fix race in trace_open and buffer resize call
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>
---
kernel/trace/ring_buffer.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 4bf050fcfe3b..6a790901270f 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4406,6 +4406,9 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
+ /* prevent another thread from changing buffer sizes */
+ mutex_lock(&buffer->mutex);
+
atomic_inc(&buffer->resize_disabled);
atomic_inc(&cpu_buffer->record_disabled);
@@ -4428,6 +4431,8 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&buffer->resize_disabled);
+
+ mutex_unlock(&buffer->mutex);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
--
2.17.1
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