Trace ring buffer can no longer record anything after executing like: # cd /sys/kernel/tracing # cat tracing_cpumask fff # echo 0 > tracing_cpumask # echo 1 > snapshot # echo fff > tracing_cpumask # echo "hello world" > trace_marker -bash: echo: write error: Bad file descriptor
The root cause is that: 1. After `echo 0 > tracing_cpumask`, 'record_disabled' of cpu buffers in 'tr->array_buffer.buffer' became 1 (see tracing_set_cpumask()); 2. After `echo 1 > snapshot`, 'tr->array_buffer.buffer' is swapped with 'tr->max_buffer.buffer', then the 'record_disabled' became 0 (see update_max_tr()); 3. After `echo fff > tracing_cpumask`, the 'record_disabled' become -1; Then array_buffer and max_buffer are both unavailable due to value of 'record_disabled' is not 0.
To fix it, enable or disable both array_buffer and max_buffer at the same time in tracing_set_cpumask().
Fixes: 71babb2705e2 ("tracing: change CPU ring buffer state from tracing_cpumask") Signed-off-by: Zheng Yejian zhengyejian1@huawei.com --- kernel/trace/trace.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index b8870078ef58..691ec4d4cd19 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -5277,11 +5277,13 @@ int tracing_set_cpumask(struct trace_array *tr, !cpumask_test_cpu(cpu, tracing_cpumask_new)) { atomic_inc(&per_cpu_ptr(tr->array_buffer.data, cpu)->disabled); ring_buffer_record_disable_cpu(tr->array_buffer.buffer, cpu); + ring_buffer_record_disable_cpu(tr->max_buffer.buffer, cpu); } if (!cpumask_test_cpu(cpu, tr->tracing_cpumask) && cpumask_test_cpu(cpu, tracing_cpumask_new)) { atomic_dec(&per_cpu_ptr(tr->array_buffer.data, cpu)->disabled); ring_buffer_record_enable_cpu(tr->array_buffer.buffer, cpu); + ring_buffer_record_enable_cpu(tr->max_buffer.buffer, cpu); } } arch_spin_unlock(&tr->max_lock);