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Stephen Boyd
5ae8aabeae
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 <[email protected]> Signed-off-by: Stephen Boyd <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Will Deacon <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Josh Cartwright <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: John Stultz <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]>