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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id i16sm87516otc.61.2021.01.05.13.13.51 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Tue, 05 Jan 2021 13:13:51 -0800 (PST) Date: Tue, 5 Jan 2021 13:13:40 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Linus Torvalds cc: Hugh Dickins , Andrew Morton , Matthew Wilcox , syzbot , Linux Kernel Mailing List , Linux-MM , syzkaller-bugs Subject: Re: kernel BUG at mm/page-writeback.c:LINE! In-Reply-To: Message-ID: References: <000000000000886dbd05b7ffa8db@google.com> <20210104124153.0992b1f7fd1a145e193a333f@linux-foundation.org> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 5 Jan 2021, Linus Torvalds wrote: > On Tue, Jan 5, 2021 at 11:31 AM Linus Torvalds > wrote: > > On Mon, Jan 4, 2021 at 7:29 PM Hugh Dickins wrote: > > > > > > > So the one-liner of changing the "if" to "while" in > > > > wait_on_page_writeback() should get us back to what we used to do. > > > > > > I think that is the realistic way to go. > > > > Yeah, that's what I'll do. > > I took your "way to go" statement as an ack, and made it all be commit > c2407cf7d22d ("mm: make wait_on_page_writeback() wait for multiple > pending writebacks"). Great, thanks, I see it now. 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. But if it were reverted, we'd need some other fix for the PageTail part of it; and I still cannot think of anywhere else where we knowingly operated on a struct page without holding a reference; and there have been no adverse reports on its extra get_page+put_page. So I think it's safest to leave it in. Hugh