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Subject[PATCH v1] trace: Fix race in trace_open and buffer resize call
Date
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.

Signed-off-by: Gaurav Kohli <gkohli@codeaurora.org>
Cc: stable@vger.kernel.org
---
Changes since v0:
-Addressed Steven's review comments.

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 93ef0ab..15bf28b 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4866,6 +4866,9 @@ void ring_buffer_reset_cpu(struct trace_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(&cpu_buffer->resize_disabled);
atomic_inc(&cpu_buffer->record_disabled);

@@ -4876,6 +4879,8 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)

atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&cpu_buffer->resize_disabled);
+
+ mutex_unlock(&buffer->mutex);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);

@@ -4889,6 +4894,9 @@ void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;

+ /* prevent another thread from changing buffer sizes */
+ mutex_lock(&buffer->mutex);
+
for_each_online_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];

@@ -4907,6 +4915,8 @@ void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&cpu_buffer->resize_disabled);
}
+
+ mutex_unlock(&buffer->mutex);
}

/**
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
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