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sched: Deal with non-atomic min_vruntime reads on 32bits

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In order to avoid reading partial updated min_vruntime values on 32bit
implement a seqcount like solution.

Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110405152729.111378493@chello.nl
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2011-04-05 17:23:48 +02:00 • committed by Ingo Molnar
commit 3fe1698b7f
2 changed files with 20 additions and 2 deletions
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3
kernel/sched.c
View file

@ -312,6 +312,9 @@ struct cfs_rq {
u64 exec_clock; u64 exec_clock;
u64 min_vruntime; u64 min_vruntime;
#ifndef CONFIG_64BIT
u64 min_vruntime_copy;
#endif
struct rb_root tasks_timeline; struct rb_root tasks_timeline;
struct rb_node *rb_leftmost; struct rb_node *rb_leftmost;

19
kernel/sched_fair.c
View file

@ -358,6 +358,10 @@ static void update_min_vruntime(struct cfs_rq *cfs_rq)
} }
cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime); cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
#ifndef CONFIG_64BIT
smp_wmb();
cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
#endif
} }
/* /*
@ -1376,10 +1380,21 @@ static void task_waking_fair(struct task_struct *p)
{ {
struct sched_entity *se = &p->se; struct sched_entity *se = &p->se;
struct cfs_rq *cfs_rq = cfs_rq_of(se); struct cfs_rq *cfs_rq = cfs_rq_of(se);
u64 min_vruntime;
lockdep_assert_held(&task_rq(p)->lock); #ifndef CONFIG_64BIT
u64 min_vruntime_copy;
se->vruntime -= cfs_rq->min_vruntime; do {
min_vruntime_copy = cfs_rq->min_vruntime_copy;
smp_rmb();
min_vruntime = cfs_rq->min_vruntime;
} while (min_vruntime != min_vruntime_copy);
#else
min_vruntime = cfs_rq->min_vruntime;
#endif
se->vruntime -= min_vruntime;
} }
#ifdef CONFIG_FAIR_GROUP_SCHED #ifdef CONFIG_FAIR_GROUP_SCHED