Update a stale comment from the old vtime era and document some locking that might be non obvious.
Signed-off-by: Frederic Weisbecker <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Li Zhong <[email protected]> Cc: Mike Galbraith <[email protected]> Cc: Kevin Hilman <[email protected]> --- include/linux/context_tracking.h | 8 ++------ kernel/sched/cputime.c | 7 +++++++ 2 files changed, 9 insertions(+), 6 deletions(-) diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h index 5984f25..12045ce 100644 --- a/include/linux/context_tracking.h +++ b/include/linux/context_tracking.h @@ -72,8 +72,8 @@ extern void guest_exit(void); static inline void guest_enter(void) { /* - * This is running in ioctl context so we can avoid - * the call to vtime_account() with its unnecessary idle check. + * This is running in ioctl context so its safe + * to assume the pending cputime to flush is stime. */ vtime_account_system(current); current->flags |= PF_VCPU; @@ -81,10 +81,6 @@ static inline void guest_enter(void) static inline void guest_exit(void) { - /* - * This is running in ioctl context so we can avoid - * the call to vtime_account() with its unnecessary idle check. - */ vtime_account_system(current); current->flags &= ~PF_VCPU; } diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index a7959e0..223a35e 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -712,6 +712,13 @@ void vtime_user_enter(struct task_struct *tsk) void vtime_guest_enter(struct task_struct *tsk) { + /* + * The flags must be updated under the lock with + * the vtime_snap flush and update. + * That enforces a right ordering and update sequence + * synchronization against the reader (task_gtime()) + * that can thus safely catch up with a tickless delta. + */ write_seqlock(&tsk->vtime_seqlock); __vtime_account_system(tsk); current->flags |= PF_VCPU; -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
