Patch "ring-buffer: Force absolute timestamp on discard of event" has been added to the 6.1-stable tree

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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

    ring-buffer: Force absolute timestamp on discard of event

to the 6.1-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:
     ring-buffer-force-absolute-timestamp-on-discard-of-e.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 1249c67fa9a9b3ae207b53fcbefa8dac3acbc308
Author: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Date:   Wed Dec 6 10:02:44 2023 -0500

    ring-buffer: Force absolute timestamp on discard of event
    
    [ Upstream commit b2dd797543cfa6580eac8408dd67fa02164d9e56 ]
    
    There's a race where if an event is discarded from the ring buffer and an
    interrupt were to happen at that time and insert an event, the time stamp
    is still used from the discarded event as an offset. This can screw up the
    timings.
    
    If the event is going to be discarded, set the "before_stamp" to zero.
    When a new event comes in, it compares the "before_stamp" with the
    "write_stamp" and if they are not equal, it will insert an absolute
    timestamp. This will prevent the timings from getting out of sync due to
    the discarded event.
    
    Link: https://lore.kernel.org/linux-trace-kernel/20231206100244.5130f9b3@xxxxxxxxxxxxxxxxxx
    
    Cc: stable@xxxxxxxxxxxxxxx
    Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
    Cc: Mark Rutland <mark.rutland@xxxxxxx>
    Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
    Fixes: 6f6be606e763f ("ring-buffer: Force before_stamp and write_stamp to be different on discard")
    Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index f3c4bb54a0485..c02a4cb879913 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3025,22 +3025,19 @@ rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
 			local_read(&bpage->write) & ~RB_WRITE_MASK;
 		unsigned long event_length = rb_event_length(event);
 
+		/*
+		 * For the before_stamp to be different than the write_stamp
+		 * to make sure that the next event adds an absolute
+		 * value and does not rely on the saved write stamp, which
+		 * is now going to be bogus.
+		 */
+		rb_time_set(&cpu_buffer->before_stamp, 0);
+
 		/* Something came in, can't discard */
 		if (!rb_time_cmpxchg(&cpu_buffer->write_stamp,
 				       write_stamp, write_stamp - delta))
 			return 0;
 
-		/*
-		 * It's possible that the event time delta is zero
-		 * (has the same time stamp as the previous event)
-		 * in which case write_stamp and before_stamp could
-		 * be the same. In such a case, force before_stamp
-		 * to be different than write_stamp. It doesn't
-		 * matter what it is, as long as its different.
-		 */
-		if (!delta)
-			rb_time_set(&cpu_buffer->before_stamp, 0);
-
 		/*
 		 * If an event were to come in now, it would see that the
 		 * write_stamp and the before_stamp are different, and assume




[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux