ring_buffer: tracing: Inherit the tracing setting to next ring buffer (73c8d894) · Commits · 戴 / test

Maintain the tracing on/off setting of the ring_buffer when switching to the trace buffer snapshot. Taking a snapshot is done by swapping the backup ring buffer (max_tr_buffer). But since the tracing on/off setting is defined by the ring buffer, when swapping it, the tracing on/off setting can also be changed. This causes a strange result like below: /sys/kernel/debug/tracing # cat tracing_on 1 /sys/kernel/debug/tracing # echo 0 > tracing_on /sys/kernel/debug/tracing # cat tracing_on 0 /sys/kernel/debug/tracing # echo 1 > snapshot /sys/kernel/debug/tracing # cat tracing_on 1 /sys/kernel/debug/tracing # echo 1 > snapshot /sys/kernel/debug/tracing # cat tracing_on 0 We don't touch tracing_on, but snapshot changes tracing_on setting each time. This is an anomaly, because user doesn't know that each "ring_buffer" stores its own tracing-enable state and the snapshot is done by swapping ring buffers. Link: http://lkml.kernel.org/r/153149929558.11274.11730609978254724394.stgit@devbox Cc: Ingo Molnar <mingo@redhat.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Tom Zanussi <tom.zanussi@linux.intel.com> Cc: Hiraku Toyooka <hiraku.toyooka@cybertrust.co.jp> Cc: stable@vger.kernel.org Fixes: ("tracing: Make a snapshot feature available from userspace") Signed-off-by:

Masami Hiramatsu <mhiramat@kernel.org> [ Updated commit log and comment in the code ] Signed-off-by:

Steven Rostedt (VMware) <rostedt@goodmis.org>

include/linux/ring_buffer.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -165,6 +165,7 @@ void ring_buffer_record_enable(struct ring_buffer *buffer);
		void ring_buffer_record_off(struct ring_buffer *buffer);
		void ring_buffer_record_on(struct ring_buffer *buffer);
		int ring_buffer_record_is_on(struct ring_buffer *buffer);
		int ring_buffer_record_is_set_on(struct ring_buffer *buffer);
		void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu);
		void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu);

kernel/trace/ring_buffer.c

+16 −0

Original line number	Diff line number	Diff line
		@@ -3226,6 +3226,22 @@ int ring_buffer_record_is_on(struct ring_buffer *buffer)
		return !atomic_read(&buffer->record_disabled);
		}

		/**
		* ring_buffer_record_is_set_on - return true if the ring buffer is set writable
		* @buffer: The ring buffer to see if write is set enabled
		*
		* Returns true if the ring buffer is set writable by ring_buffer_record_on().
		* Note that this does NOT mean it is in a writable state.
		*
		* It may return true when the ring buffer has been disabled by
		* ring_buffer_record_disable(), as that is a temporary disabling of
		* the ring buffer.
		*/
		int ring_buffer_record_is_set_on(struct ring_buffer *buffer)
		{
		return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF);
		}

		/**
		* ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
		* @buffer: The ring buffer to stop writes to.

kernel/trace/trace.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -1373,6 +1373,12 @@ update_max_tr(struct trace_array tr, struct task_struct tsk, int cpu)

		arch_spin_lock(&tr->max_lock);

		/* Inherit the recordable setting from trace_buffer */
		if (ring_buffer_record_is_set_on(tr->trace_buffer.buffer))
		ring_buffer_record_on(tr->max_buffer.buffer);
		else
		ring_buffer_record_off(tr->max_buffer.buffer);

		swap(tr->trace_buffer.buffer, tr->max_buffer.buffer);

		__update_max_tr(tr, tsk, cpu);

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