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Date: Sat, 2 Oct 2021 10:22:23 +0800 From: Rongwei Wang <rongwei.wang@...ux.alibaba.com> To: Hugh Dickins <hughd@...gle.com>, Matthew Wilcox <willy@...radead.org> Cc: Song Liu <song@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Linux MM <linux-mm@...ck.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, William Kucharski <william.kucharski@...cle.com> Subject: Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page cache On 10/1/21 12:49 AM, Hugh Dickins wrote: > On Thu, 30 Sep 2021, Matthew Wilcox wrote: >> On Wed, Sep 29, 2021 at 10:24:44PM -0700, Hugh Dickins wrote: >>> >>> Aside from the above page->index mischeck in find_lock_entries(), >>> I now think this bug needs nothing more than simply removing the >>> VM_BUG_ON_PAGE(PageTail(page), page) from truncate_inode_page(). >> >> I don't think that's right. This bug was also observed when calling >> truncate(), so there's clearly a situation where two concurrent calls >> to truncate_pagecache() leaves a THP in the cache. > > I assume you're thinking of one of the fuzzer blkdev ones: > https://lore.kernel.org/linux-mm/CACkBjsbtF_peC7N_4mRfHML_BeiPe+O9DahTfr84puSG_J9rcQ@mail.gmail.com/ > or > https://lore.kernel.org/lkml/CACkBjsYwLYLRmX8GpsDpMthagWOjWWrNxqY6ZLNQVr6yx+f5vA@mail.gmail.com/ > > I haven't started on those ones yet: yes, I imagine one or both of those > will need a further fix (S_ISREG() check somewhere if we're lucky; but > could well be nastier); but for the bug in this thread, I expect > removing the VM_BUG_ON_PAGE(PageTail) to be enough. Thanks for your advices! I'm so sorry that delay the test due to my recent vacation. I plan to start further test tomorrow. I think removing the VM_BUG_ON_PAGE(PageTail) is a good idea, but also think using filemap_invalidate_lock is safer and necessary. And of course, this is just my own view! So, now, I tend to use filemap_invalidate_lock and either check page mapping again or remove VM_BUG_ON_PAGE(PageTail). Anyway, I will run more tests and then give feedback. Thanks! > > If you're thinking of something else, please send a link if you can - thanks. > > Hugh >
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