Messages in this thread Patch in this message | | | Date | Wed, 11 Jan 2012 22:17:09 -0800 | From | tip-bot for Peter Zijlstra <> | Subject | [tip:sched/urgent] sched: Fix lockup by limiting load-balance retries on lock-break |
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Commit-ID: bced76aeaca03b45e3b4bdb868cada328e497847 Gitweb: http://git.kernel.org/tip/bced76aeaca03b45e3b4bdb868cada328e497847 Author: Peter Zijlstra <a.p.zijlstra@chello.nl> AuthorDate: Wed, 11 Jan 2012 13:11:12 +0100 Committer: Ingo Molnar <mingo@elte.hu> 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@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> --- 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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