On Wed, Sep 25, 2019 at 11:42:42PM +0200, Frederic Weisbecker wrote: > vtime_account_system() assumes that the target task to account cputime > to is always the current task. This is most often true indeed except on > task switch where we call: > > vtime_common_task_switch(prev) > vtime_account_system(prev) > > Here prev is the scheduling-out task where we account the cputime to. It > doesn't match current that is already the scheduling-in task at this > stage of the context switch. > > So we end up checking the wrong task flags to determine if we are > accounting guest or system time to the previous task. > > As a result the wrong task is used to check if the target is running in > guest mode. We may then spuriously account or leak either system or > guest time on task switch. > > Fix this assumption and also turn vtime_guest_enter/exit() to use the > task passed in parameter as well to avoid future similar issues. > > Fixes: 2a42eb9594a1 ("sched/cputime: Accumulate vtime on top of nsec > clocksource") > Signed-off-by: Frederic Weisbecker <frede...@kernel.org> > Cc: Thomas Gleixner <t...@linutronix.de> > Cc: Rik van Riel <r...@redhat.com> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Wanpeng Li <wanpen...@tencent.com> > Cc: Ingo Molnar <mi...@kernel.org>
Thanks!