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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acl.h
// SPDX-License-Identifier: GPL-2.0
/*
* fs/f2fs/acl.h
*
* Copyright (c) 2012 Samsung Electronics Co., Ltd.
* http://www.samsung.com/
*
* Portions of this code from linux/fs/ext2/acl.h
*
* Copyright (C) 2001-2003 Andreas Gruenbacher, <agruen@suse.de>
*/
#ifndef __F2FS_ACL_H__
#define __F2FS_ACL_H__
#include <linux/posix_acl_xattr.h>
#define F2FS_ACL_VERSION 0x0001
struct f2fs_acl_entry {
__le16 e_tag;
__le16 e_perm;
__le32 e_id;
};
struct f2fs_acl_entry_short {
__le16 e_tag;
__le16 e_perm;
};
struct f2fs_acl_header {
__le32 a_version;
};
#ifdef CONFIG_F2FS_FS_POSIX_ACL
extern struct posix_acl *f2fs_get_acl(struct inode *, int);
extern int f2fs_set_acl(struct inode *, struct posix_acl *, int);
extern int f2fs_init_acl(struct inode *, struct inode *, struct page *,
struct page *);
#else
#define f2fs_get_acl NULL
#define f2fs_set_acl NULL
static inline int f2fs_init_acl(struct inode *inode, struct inode *dir,
struct page *ipage, struct page *dpage)
{
return 0;
}
#endif
#endif /* __F2FS_ACL_H__ */
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