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Commit 7cc78f8f authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Linus Torvalds
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context_tracking: Restore previous state in schedule_user 



It appears that some SCHEDULE_USER (asm for schedule_user) callers
in arch/x86/kernel/entry_64.S are called from RCU kernel context,
and schedule_user will return in RCU user context.  This causes RCU
warnings and possible failures.

This is intended to be a minimal fix suitable for 3.18.

Reported-and-tested-by: default avatarDave Jones <davej@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Acked-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarAndy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ebcd241a

kernel/sched/core.c

+6 −2
Original line number Diff line number Diff line
@@ -2874,10 +2874,14 @@ asmlinkage __visible void __sched schedule_user(void) 
	 * or we have been woken up remotely but the IPI has not yet arrived,

	 * we haven't yet exited the RCU idle mode. Do it here manually until

	 * we find a better solution.

	 *

	 * NB: There are buggy callers of this function.  Ideally we

	 * should warn if prev_state != IN_USER, but that will trigger

	 * too frequently to make sense yet.

	 */

	user_exit();

	enum ctx_state prev_state = exception_enter();

	schedule();

	user_enter();

	exception_exit(prev_state);

}

#endif