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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id x62sm664859oig.24.2021.09.30.09.49.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Sep 2021 09:49:33 -0700 (PDT) Date: Thu, 30 Sep 2021 09:49:21 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.anvils To: Matthew Wilcox cc: Hugh Dickins , Song Liu , Rongwei Wang , Andrew Morton , Linux MM , Linux Kernel Mailing List , William Kucharski Subject: Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page cache In-Reply-To: Message-ID: References: <68737431-01d2-e6e3-5131-7d7c731e49ae@linux.alibaba.com> <67906bf5-4de9-8433-3d70-cc8fc5cc2347@linux.alibaba.com> <3d264ed9-f8fd-60d4-7125-f9f745ebeb52@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. If you're thinking of something else, please send a link if you can - thanks. Hugh