Commit-ID: bced76aeaca03b45e3b4bdb868cada328e497847
Gitweb: http://git.kernel.org/tip/bced76aeaca03b45e3b4bdb868cada328e497847
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Wed, 11 Jan 2012 13:11:12 +0100
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Wed, 11 Jan 2012 17:15:12 +0100
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@xxxxxxxxx>
Tested-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Reported-by: David Ahern <dsahern@xxxxxxxxx>
[ logic cleanup as suggested by Eric ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1326297936.2442.157.camel@twins
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
kernel/sched/fair.c | 10 +++++++---
1 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8e42de9..84adb2d 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;
}
--
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