Hi Steven, please let us know, if below looks good to you or need modifications.
Thanks Gaurav On 9/24/2020 7:25 PM, Gaurav Kohli wrote:
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 <[email protected]> Cc: [email protected] --- 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); }/**
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