Revision 6e2df0581f569038719cf2bc2b3baa3fcc83cab4 authored by Peter Zijlstra on 08 November 2019, 10:11:52 UTC, committed by Peter Zijlstra on 08 November 2019, 21:34:14 UTC
Commit 67692435c411 ("sched: Rework pick_next_task() slow-path") inadvertly introduced a race because it changed a previously unexplored dependency between dropping the rq->lock and sched_class::put_prev_task(). The comments about dropping rq->lock, in for example newidle_balance(), only mentions the task being current and ->on_cpu being set. But when we look at the 'change' pattern (in for example sched_setnuma()): queued = task_on_rq_queued(p); /* p->on_rq == TASK_ON_RQ_QUEUED */ running = task_current(rq, p); /* rq->curr == p */ if (queued) dequeue_task(...); if (running) put_prev_task(...); /* change task properties */ if (queued) enqueue_task(...); if (running) set_next_task(...); It becomes obvious that if we do this after put_prev_task() has already been called on @p, things go sideways. This is exactly what the commit in question allows to happen when it does: prev->sched_class->put_prev_task(rq, prev, rf); if (!rq->nr_running) newidle_balance(rq, rf); The newidle_balance() call will drop rq->lock after we've called put_prev_task() and that allows the above 'change' pattern to interleave and mess up the state. Furthermore, it turns out we lost the RT-pull when we put the last DL task. Fix both problems by extracting the balancing from put_prev_task() and doing a multi-class balance() pass before put_prev_task(). Fixes: 67692435c411 ("sched: Rework pick_next_task() slow-path") Reported-by: Quentin Perret <qperret@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Quentin Perret <qperret@google.com> Tested-by: Valentin Schneider <valentin.schneider@arm.com>
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xattr.h
/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
* Squashfs - a compressed read only filesystem for Linux
*
* Copyright (c) 2010
* Phillip Lougher <phillip@squashfs.org.uk>
*
* xattr.h
*/
#ifdef CONFIG_SQUASHFS_XATTR
extern __le64 *squashfs_read_xattr_id_table(struct super_block *, u64,
u64 *, int *);
extern int squashfs_xattr_lookup(struct super_block *, unsigned int, int *,
unsigned int *, unsigned long long *);
#else
static inline __le64 *squashfs_read_xattr_id_table(struct super_block *sb,
u64 start, u64 *xattr_table_start, int *xattr_ids)
{
ERROR("Xattrs in filesystem, these will be ignored\n");
*xattr_table_start = start;
return ERR_PTR(-ENOTSUPP);
}
static inline int squashfs_xattr_lookup(struct super_block *sb,
unsigned int index, int *count, unsigned int *size,
unsigned long long *xattr)
{
return 0;
}
#define squashfs_listxattr NULL
#define squashfs_xattr_handlers NULL
#endif
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