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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	 syzbot <syzbot+2fc0712f8f8b8b8fa0ef@syzkaller.appspotmail.com>,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	 syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Subject: Re: kernel BUG at mm/page-writeback.c:LINE!
Date: Tue, 5 Jan 2021 13:22:49 -0800	[thread overview]
Message-ID: <CAHk-=wiGHdRRmZtrcUt6g6hmATkmueNVLNnSHSBoUp-v-Qy5sw@mail.gmail.com> (raw)
In-Reply-To: <alpine.LSU.2.11.2101051235500.5906@eggly.anvils>

On Tue, Jan 5, 2021 at 1:13 PM Hugh Dickins <hughd@google.com> wrote:
>
> I was going to raise a question, whether you should now revert
> 073861ed77b6 ("mm: fix VM_BUG_ON(PageTail) and BUG_ON(PageWriteback)"):
> which would not have gone in like that if c2407cf7d22d were already in.

Honestly, even if it wasn't for that PageTail issue, I think
073861ed77b6 is just the right thing to do anyway. It just feels _so_
much safer to not have the possibility of that page wait thing
following while the page is possibly then being free'd and re-used at
the same time.

So I think the only reason to revert that commit would be if we were
to find that it's a huge performance problem to raise the page
refcount temporarily. Which I think is very unlikely (since we already
dirty the page structure due to the page flags modification - although
they are far enough apart that it might be a different cacheline).

                   Linus


  reply	other threads:[~2021-01-05 21:23 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-03 14:19 syzbot
2021-01-04 20:41 ` Andrew Morton
2021-01-04 21:52   ` Linus Torvalds
2021-01-05  3:28     ` Hugh Dickins
2021-01-05 19:31       ` Linus Torvalds
2021-01-05 19:53         ` Linus Torvalds
2021-01-05 21:13           ` Hugh Dickins
2021-01-05 21:22             ` Linus Torvalds [this message]
2021-01-05 21:34               ` Matthew Wilcox
2021-01-09  2:04           ` Linus Torvalds
2021-01-12 10:44             ` Jan Kara
2021-01-12 17:35               ` Linus Torvalds

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