From 5ae8aabeaec3fe69c4fb21cbe5b17b72b35b5892 Mon Sep 17 00:00:00 2001 From: Stephen Boyd Date: Mon, 17 Feb 2014 10:45:36 -0800 Subject: [PATCH] sched_clock: Prevent callers from seeing half-updated data The generic sched_clock registration function was previously done lockless, due to the fact that it was expected to be called only once. However, now there are systems that may register multiple sched_clock sources, for which the lack of locking has casued problems: If two sched_clock sources are registered we may end up in a situation where a call to sched_clock() may be accessing the epoch cycle count for the old counter and the cycle count for the new counter. This can lead to confusing results where sched_clock() values jump and then are reset to 0 (due to the way the registration function forces the epoch_ns to be 0). Fix this by reorganizing the registration function to hold the seqlock for as short a time as possible while we update the clock_data structure for a new counter. We also put any accumulated time into epoch_ns instead of resetting the time to 0 so that the clock doesn't reset after each successful registration. [jstultz: Added extra context to the commit message] Reported-by: Will Deacon Signed-off-by: Stephen Boyd Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Will Deacon Cc: Peter Zijlstra Cc: Josh Cartwright Link: http://lkml.kernel.org/r/1392662736-7803-2-git-send-email-john.stultz@linaro.org Signed-off-by: John Stultz Signed-off-by: Thomas Gleixner --- Reading git-format-patch failed