From 68e7a4d66b0ce04bf18ff2ffded5596ab3618585 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 25 Sep 2019 23:42:42 +0200 Subject: sched/vtime: Fix guest/system mis-accounting on task switch 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. Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Cc: Wanpeng Li Fixes: 2a42eb9594a1 ("sched/cputime: Accumulate vtime on top of nsec clocksource") Link: https://lkml.kernel.org/r/20190925214242.21873-1-frederic@kernel.org Signed-off-by: Ingo Molnar --- kernel/sched/cputime.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'kernel/sched') diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 2305ce89a26c..46ed4e1383e2 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -740,7 +740,7 @@ void vtime_account_system(struct task_struct *tsk) write_seqcount_begin(&vtime->seqcount); /* We might have scheduled out from guest path */ - if (current->flags & PF_VCPU) + if (tsk->flags & PF_VCPU) vtime_account_guest(tsk, vtime); else __vtime_account_system(tsk, vtime); @@ -783,7 +783,7 @@ void vtime_guest_enter(struct task_struct *tsk) */ write_seqcount_begin(&vtime->seqcount); __vtime_account_system(tsk, vtime); - current->flags |= PF_VCPU; + tsk->flags |= PF_VCPU; write_seqcount_end(&vtime->seqcount); } EXPORT_SYMBOL_GPL(vtime_guest_enter); @@ -794,7 +794,7 @@ void vtime_guest_exit(struct task_struct *tsk) write_seqcount_begin(&vtime->seqcount); vtime_account_guest(tsk, vtime); - current->flags &= ~PF_VCPU; + tsk->flags &= ~PF_VCPU; write_seqcount_end(&vtime->seqcount); } EXPORT_SYMBOL_GPL(vtime_guest_exit); -- cgit v1.2.3-58-ga151