Patch "tracing: Fix cpu buffers unavailable due to 'record_disabled' missed" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    tracing: Fix cpu buffers unavailable due to 'record_disabled' missed

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:
     tracing-fix-cpu-buffers-unavailable-due-to-record_di.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.



commit ed62cb20c8509994b2c4a0075c07e862dfc2f535
Author: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
Date:   Sat Aug 5 11:38:15 2023 +0800

    tracing: Fix cpu buffers unavailable due to 'record_disabled' missed
    
    [ Upstream commit b71645d6af10196c46cbe3732de2ea7d36b3ff6d ]
    
    Trace ring buffer can no longer record anything after executing
    following commands at the shell prompt:
    
      # cd /sys/kernel/tracing
      # cat tracing_cpumask
      fff
      # echo 0 > tracing_cpumask
      # echo 1 > snapshot
      # echo fff > tracing_cpumask
      # echo 1 > tracing_on
      # 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().
    
    Link: https://lkml.kernel.org/r/20230805033816.3284594-2-zhengyejian1@xxxxxxxxxx
    
    Cc: <mhiramat@xxxxxxxxxx>
    Cc: <vnagarnaik@xxxxxxxxxx>
    Cc: <shuah@xxxxxxxxxx>
    Fixes: 71babb2705e2 ("tracing: change CPU ring buffer state from tracing_cpumask")
    Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
    Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d4c381f06b7b2..edc58133ed5ed 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5171,11 +5171,17 @@ 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);
+#ifdef CONFIG_TRACER_MAX_TRACE
+			ring_buffer_record_disable_cpu(tr->max_buffer.buffer, cpu);
+#endif
 		}
 		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);
+#ifdef CONFIG_TRACER_MAX_TRACE
+			ring_buffer_record_enable_cpu(tr->max_buffer.buffer, cpu);
+#endif
 		}
 	}
 	arch_spin_unlock(&tr->max_lock);