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From: Alexander Duyck <alexander.duyck@gmail.com>
To: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>,
	kbuild test robot <lkp@intel.com>,
	 Rong Chen <rong.a.chen@intel.com>,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	 "Kirill A. Shutemov" <kirill@shutemov.name>,
	Hugh Dickins <hughd@google.com>,
	 LKML <linux-kernel@vger.kernel.org>,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	 linux-mm <linux-mm@kvack.org>,
	Shakeel Butt <shakeelb@google.com>,
	 Matthew Wilcox <willy@infradead.org>,
	Johannes Weiner <hannes@cmpxchg.org>, Tejun Heo <tj@kernel.org>,
	 cgroups@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	 Wei Yang <richard.weiyang@gmail.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	 Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [RFC PATCH 1/3] mm: Drop locked from isolate_migratepages_block
Date: Thu, 13 Aug 2020 07:26:42 -0700
Message-ID: <CAKgT0UfO0j9yQCiQD+QDpNPCGncfH-+yP+qmEYGA_Fz=jmqAUQ@mail.gmail.com> (raw)
In-Reply-To: <4403f572-03c3-3061-6fc4-f56e3b6d7b67@linux.alibaba.com>

On Thu, Aug 13, 2020 at 12:45 AM Alex Shi <alex.shi@linux.alibaba.com> wrote:
>
>
>
> 在 2020/8/13 下午12:02, Alexander Duyck 写道:
> > -             rcu_read_lock();
> > -             lruvec = mem_cgroup_page_lruvec(page, pgdat);
> > -
> >               /* If we already hold the lock, we can skip some rechecking */
> > -             if (lruvec != locked) {
> > -                     if (locked)
> > -                             unlock_page_lruvec_irqrestore(locked, flags);
> > +             if (!lruvec || !lruvec_holds_page_lru_lock(page, lruvec)) {
>
> Ops, lruvec_holds_page_lru_lock need rcu_read_lock.

How so? The reason I wrote lruvec_holds_page_lru_lock the way I did is
that it is simply comparing the pointers held by the page and the
lruvec. It is never actually accessing any of the values, just the
pointers. As such we should be able to compare the two since the
lruvec is still locked and the the memcg and pgdat held by the lruvec
should not be changed. Likewise with the page pointers assuming the
values match.

> > +                     if (lruvec)
> > +                             unlock_page_lruvec_irqrestore(lruvec, flags);
> >
> > +                     lruvec = mem_cgroup_page_lruvec(page, pgdat);
> >                       compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
> > -                     locked = lruvec;
> >                       rcu_read_unlock();
> >
>
> and some bugs:
> [  534.564741] CPU: 23 PID: 545 Comm: kcompactd1 Kdump: loaded Tainted: G S      W         5.8.0-next-20200803-00028-g9a7ff2cd6e5c #85
> [  534.577320] Hardware name: Alibaba Alibaba Cloud ECS/Alibaba Cloud ECS, BIOS 1.0.PL.IP.P.027.02 05/29/2020
> [  534.587693] Call Trace:
> [  534.590522]  dump_stack+0x96/0xd0
> [  534.594231]  ___might_sleep.cold.90+0xff/0x115
> [  534.599102]  kcompactd+0x24b/0x370
> [  534.602904]  ? finish_wait+0x80/0x80
> [  534.606897]  ? kcompactd_do_work+0x3d0/0x3d0
> [  534.611566]  kthread+0x14e/0x170
> [  534.615182]  ? kthread_park+0x80/0x80
> [  534.619252]  ret_from_fork+0x1f/0x30
> [  535.629483] BUG: sleeping function called from invalid context at include/linux/freezer.h:57
> [  535.638691] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 545, name: kcompactd1
> [  535.647601] INFO: lockdep is turned off.

Ah, I see the bug now. It isn't the lruvec_holds_page_lru_lock that
needs the LRU lock. This is an issue as a part of a merge conflict.
There should have been an rcu_read_lock added before
mem_cgroup_page_lruvec.


  reply index

Thread overview: 102+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-25 12:59 [PATCH v17 00/21] per memcg lru lock Alex Shi
2020-07-25 12:59 ` [PATCH v17 01/21] mm/vmscan: remove unnecessary lruvec adding Alex Shi
2020-08-06  3:47   ` Alex Shi
2020-07-25 12:59 ` [PATCH v17 02/21] mm/page_idle: no unlikely double check for idle page counting Alex Shi
2020-07-25 12:59 ` [PATCH v17 03/21] mm/compaction: correct the comments of compact_defer_shift Alex Shi
2020-07-27 17:29   ` Alexander Duyck
2020-07-28 11:59     ` Alex Shi
2020-07-28 14:17       ` Alexander Duyck
2020-07-25 12:59 ` [PATCH v17 04/21] mm/compaction: rename compact_deferred as compact_should_defer Alex Shi
2020-07-25 12:59 ` [PATCH v17 05/21] mm/thp: move lru_add_page_tail func to huge_memory.c Alex Shi
2020-07-25 12:59 ` [PATCH v17 06/21] mm/thp: clean up lru_add_page_tail Alex Shi
2020-07-25 12:59 ` [PATCH v17 07/21] mm/thp: remove code path which never got into Alex Shi
2020-07-25 12:59 ` [PATCH v17 08/21] mm/thp: narrow lru locking Alex Shi
2020-07-25 12:59 ` [PATCH v17 09/21] mm/memcg: add debug checking in lock_page_memcg Alex Shi
2020-07-25 12:59 ` [PATCH v17 10/21] mm/swap: fold vm event PGROTATED into pagevec_move_tail_fn Alex Shi
2020-07-25 12:59 ` [PATCH v17 11/21] mm/lru: move lru_lock holding in func lru_note_cost_page Alex Shi
2020-08-05 21:18   ` Alexander Duyck
2020-07-25 12:59 ` [PATCH v17 12/21] mm/lru: move lock into lru_note_cost Alex Shi
2020-07-25 12:59 ` [PATCH v17 13/21] mm/lru: introduce TestClearPageLRU Alex Shi
2020-07-29  3:53   ` Alex Shi
2020-08-05 22:43     ` Alexander Duyck
2020-08-06  1:54       ` Alex Shi
2020-08-06 14:41         ` Alexander Duyck
2020-07-25 12:59 ` [PATCH v17 14/21] mm/compaction: do page isolation first in compaction Alex Shi
2020-08-04 21:35   ` Alexander Duyck
2020-08-06 18:38   ` Alexander Duyck
2020-08-07  3:24     ` Alex Shi
2020-08-07 14:51       ` Alexander Duyck
2020-08-10 13:10         ` Alex Shi
2020-08-10 14:41           ` Alexander Duyck
2020-08-11  8:22             ` Alex Shi
2020-08-11 14:47               ` Alexander Duyck
2020-08-12 11:43                 ` Alex Shi
2020-08-12 12:16                   ` Alex Shi
2020-08-12 16:51                   ` Alexander Duyck
2020-08-13  1:46                     ` Alex Shi
2020-08-13  2:17                       ` Alexander Duyck
2020-08-13  3:52                         ` Alex Shi
2020-08-13  4:02                       ` [RFC PATCH 0/3] " Alexander Duyck
2020-08-13  4:02                         ` [RFC PATCH 1/3] mm: Drop locked from isolate_migratepages_block Alexander Duyck
2020-08-13  6:56                           ` Alex Shi
2020-08-13 14:32                             ` Alexander Duyck
2020-08-14  7:25                               ` Alex Shi
2020-08-13  7:44                           ` Alex Shi
2020-08-13 14:26                             ` Alexander Duyck [this message]
2020-08-13  4:02                         ` [RFC PATCH 2/3] mm: Drop use of test_and_set_skip in favor of just setting skip Alexander Duyck
2020-08-14  7:19                           ` Alex Shi
2020-08-14 14:24                             ` Alexander Duyck
2020-08-14 21:15                               ` Alexander Duyck
2020-08-15  9:49                                 ` Alex Shi
2020-08-17 15:38                                   ` Alexander Duyck
2020-08-18  6:50                           ` Alex Shi
2020-08-13  4:02                         ` [RFC PATCH 3/3] mm: Identify compound pages sooner in isolate_migratepages_block Alexander Duyck
2020-08-14  7:20                           ` Alex Shi
2020-08-17 22:58   ` [PATCH v17 14/21] mm/compaction: do page isolation first in compaction Alexander Duyck
2020-07-25 12:59 ` [PATCH v17 15/21] mm/thp: add tail pages into lru anyway in split_huge_page() Alex Shi
2020-07-25 12:59 ` [PATCH v17 16/21] mm/swap: serialize memcg changes in pagevec_lru_move_fn Alex Shi
2020-07-25 12:59 ` [PATCH v17 17/21] mm/lru: replace pgdat lru_lock with lruvec lock Alex Shi
2020-07-27 23:34   ` Alexander Duyck
2020-07-28  7:15     ` Alex Shi
2020-07-28 11:19     ` Alex Shi
2020-07-28 14:54       ` Alexander Duyck
2020-07-29  1:00         ` Alex Shi
2020-07-29  1:27           ` Alexander Duyck
2020-07-29  2:27             ` Alex Shi
2020-07-28 15:39     ` Alex Shi
2020-07-28 15:55       ` Alexander Duyck
2020-07-29  0:48         ` Alex Shi
2020-07-29  3:54   ` Alex Shi
2020-08-06  7:41   ` Alex Shi
2020-07-25 12:59 ` [PATCH v17 18/21] mm/lru: introduce the relock_page_lruvec function Alex Shi
2020-07-29 17:52   ` Alexander Duyck
2020-07-30  6:08     ` Alex Shi
2020-07-31 14:20       ` Alexander Duyck
2020-07-31 21:14   ` [PATCH RFC] mm: Add function for testing if the current lruvec lock is valid alexander.h.duyck
2020-07-31 23:54     ` Alex Shi
2020-08-02 18:20       ` Alexander Duyck
2020-08-04  6:13         ` Alex Shi
2020-07-25 12:59 ` [PATCH v17 19/21] mm/vmscan: use relock for move_pages_to_lru Alex Shi
2020-08-03 22:49   ` Alexander Duyck
2020-08-04  6:23     ` Alex Shi
2020-07-25 12:59 ` [PATCH v17 20/21] mm/pgdat: remove pgdat lru_lock Alex Shi
2020-08-03 22:42   ` Alexander Duyck
2020-08-03 22:45     ` Alexander Duyck
2020-08-04  6:22       ` Alex Shi
2020-07-25 12:59 ` [PATCH v17 21/21] mm/lru: revise the comments of lru_lock Alex Shi
2020-08-03 22:37   ` Alexander Duyck
2020-08-04 10:04     ` Alex Shi
2020-08-04 14:29       ` Alexander Duyck
2020-08-06  1:39         ` Alex Shi
2020-08-06 16:27           ` Alexander Duyck
2020-07-27  5:40 ` [PATCH v17 00/21] per memcg lru lock Alex Shi
2020-07-29 14:49   ` Alex Shi
2020-07-29 18:06     ` Hugh Dickins
2020-07-30  2:16       ` Alex Shi
2020-08-03 15:07         ` Michal Hocko
2020-08-04  6:14           ` Alex Shi
2020-07-31 21:31 ` Alexander Duyck
2020-08-04  8:36 ` Alex Shi
2020-08-04  8:36 ` Alex Shi
2020-08-04  8:37 ` Alex Shi
2020-08-04  8:37 ` Alex Shi

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