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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2012-01-11 13:11:12 +0100
committerIngo Molnar <mingo@elte.hu>2012-01-11 17:15:12 +0100
commitbced76aeaca03b45e3b4bdb868cada328e497847 (patch)
treee2965b6cfecdc257a01b89ec6780b8de3b2e6d39
parent6db9dc150eabce7053c8df2a2146aa0d6748ec42 (diff)
sched: Fix lockup by limiting load-balance retries on lock-break
Eric and David reported dead machines and traced it to commit a195f004 ("sched: Fix load-balance lock-breaking"), it turns out there's still a scenario where we can end up re-trying forever. Since there is no strict forward progress guarantee in the load-balance iteration we can get stuck re-retrying the same task-set over and over. Creating a forward progress guarantee with the existing structure is somewhat non-trivial, for now simply terminate the retry loop after a few tries. Reported-by: Eric Dumazet <eric.dumazet@gmail.com> Tested-by: Eric Dumazet <eric.dumazet@gmail.com> Reported-by: David Ahern <dsahern@gmail.com> [ logic cleanup as suggested by Eric ] Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Suresh Siddha <suresh.b.siddha@intel.com> Link: http://lkml.kernel.org/r/1326297936.2442.157.camel@twins Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/sched/fair.c10
1 files changed, 7 insertions, 3 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8e42de9105f..84adb2d66cb 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3130,8 +3130,10 @@ task_hot(struct task_struct *p, u64 now, struct sched_domain *sd)
}
#define LBF_ALL_PINNED 0x01
-#define LBF_NEED_BREAK 0x02
-#define LBF_ABORT 0x04
+#define LBF_NEED_BREAK 0x02 /* clears into HAD_BREAK */
+#define LBF_HAD_BREAK 0x04
+#define LBF_HAD_BREAKS 0x0C /* count HAD_BREAKs overflows into ABORT */
+#define LBF_ABORT 0x10
/*
* can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
@@ -4508,7 +4510,9 @@ redo:
goto out_balanced;
if (lb_flags & LBF_NEED_BREAK) {
- lb_flags &= ~LBF_NEED_BREAK;
+ lb_flags += LBF_HAD_BREAK - LBF_NEED_BREAK;
+ if (lb_flags & LBF_ABORT)
+ goto out_balanced;
goto redo;
}