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author | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2015-02-13 14:49:02 +0100 |
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committer | Rafael J. Wysocki <rjw@rjwysocki.net> | 2015-02-15 19:39:40 +0100 |
commit | 060407aed56c00960c9b5f70f5d19b2823adffd7 (patch) | |
tree | 1a3e285bb6af775bfd75e4b5143548687d773861 /drivers/idle | |
parent | affe3e85ae78507cc953f3f700e0644e50844cff (diff) | |
download | op-kernel-dev-060407aed56c00960c9b5f70f5d19b2823adffd7.zip op-kernel-dev-060407aed56c00960c9b5f70f5d19b2823adffd7.tar.gz |
timekeeping: Make it safe to use the fast timekeeper while suspended
Theoretically, ktime_get_mono_fast_ns() may be executed after
timekeeping has been suspended (or before it is resumed) which
in turn may lead to undefined behavior, for example, when the
clocksource read from timekeeping_get_ns() called by it is
not accessible at that time.
Prevent that from happening by setting up a dummy readout base for
the fast timekeeper during timekeeping_suspend() such that it will
always return the same number of cycles.
After the last timekeeping_update() in timekeeping_suspend() the
clocksource is read and the result is stored as cycles_at_suspend.
The readout base from the current timekeeper is copied onto the
dummy and the ->read pointer of the dummy is set to a routine
unconditionally returning cycles_at_suspend. Next, the dummy is
passed to update_fast_timekeeper().
Then, ktime_get_mono_fast_ns() will work until the subsequent
timekeeping_resume() and the proper readout base for the fast
timekeeper will be restored by the timekeeping_update() called
right after clearing timekeeping_suspended.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Diffstat (limited to 'drivers/idle')
0 files changed, 0 insertions, 0 deletions