Commit 3fe1698b authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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



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

Reviewed-by: default avatarFrank Rowand <frank.rowand@am.sony.com>
Signed-off-by: default avatarPeter 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: default avatarIngo Molnar <mingo@elte.hu>
parent 74f8e4b2

kernel/sched.c

+3 −0
Original line number Diff line number Diff line
@@ -312,6 +312,9 @@ struct cfs_rq { 


	u64 exec_clock;

	u64 min_vruntime;

#ifndef CONFIG_64BIT

	u64 min_vruntime_copy;

#endif



	struct rb_root tasks_timeline;

	struct rb_node *rb_leftmost;

kernel/sched_fair.c

+17 −2
Original line number Diff line number Diff line
@@ -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);

#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 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

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