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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: Dave Jones <davej@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
hifive-unleashed-5.1
Andy Lutomirski 2014-12-03 15:37:08 -08:00 committed by Linus Torvalds
parent ebcd241a63
commit 7cc78f8fa0
1 changed files with 6 additions and 2 deletions
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8
kernel/sched/core.c
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@ -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