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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=M3olL4PCIPnsY+XsG6ODxFPkLeYPL3IXmw45N+fdrVs=; b=KOl/QWMYgqza+52Rqzn04PjPOzGad51V76vkA+HmYZlgqe0l0sZBUpoYmo0i4+q5K9 m4VSbTYMT10+9I7z0DPZRD4CPavmctlHPcujVLwFtKH9UHcsovv3Kc08TBS4AVZ8DKat BXF6PCe25O9iQ5nrBADNG1Rz7X8Csfxg6GsEAHybiRz6NFbxAD8tMs3CM0twAYKkqyx+ W35bt1xw59GiYjXsfoqzCYjw7ykizHs0OJXQLs229z97SqUCzgzvRS9lXhxm/NdDd5md bd2GObAo+FGUGKNZ62iDIrlYt18i1O/2hnbhrxwYNKB7BY4j/bqkmlubHzwqxwZW3iaq xDuQ== X-Gm-Message-State: AOAM533BqPQhLuPS+zcV4Sd6Q+nwqN454S1aNj0L8cOrShBQEEOlU7T3 ePVjJ+YTN4Nik9y14X7ucBX0+5LverKHXILUwHw= X-Google-Smtp-Source: ABdhPJwKXPdOdSXdF4nkEob3263c0W+0zCyiiXlZN+Nj1BOEgtL2N6pRj+PERlK2r3mZ779LDmusd/VgET5Rl4TfoEw= X-Received: by 2002:a50:8d85:: with SMTP id r5mr19954555edh.312.1633372137470; Mon, 04 Oct 2021 11:28:57 -0700 (PDT) MIME-Version: 1.0 References: <67906bf5-4de9-8433-3d70-cc8fc5cc2347@linux.alibaba.com> <3d264ed9-f8fd-60d4-7125-f9f745ebeb52@google.com> In-Reply-To: From: Yang Shi Date: Mon, 4 Oct 2021 11:28:45 -0700 Message-ID: Subject: Re: [PATCH v2 1/2] mm, thp: check page mapping when truncating page cache To: Matthew Wilcox Cc: Hugh Dickins , Song Liu , Rongwei Wang , Andrew Morton , Linux MM , Linux Kernel Mailing List , William Kucharski Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: DA1DF20061D7 X-Stat-Signature: a5ukiafj3otmaogr8zby8wy6wxu8keay Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=ED7KbLk3; spf=pass (imf26.hostedemail.com: domain of shy828301@gmail.com designates 209.85.208.49 as permitted sender) smtp.mailfrom=shy828301@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam06 X-HE-Tag: 1633372138-977912 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 Sat, Oct 2, 2021 at 10:09 AM Matthew Wilcox wrote: > > On Thu, Sep 30, 2021 at 10:39:14AM -0700, Yang Shi wrote: > > On Thu, Sep 30, 2021 at 9:49 AM Hugh Dickins wrote: > > > 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 > > > > Makes sense to me. We should be able to check S_ISREG() in khugepaged, > > if it is not a regular file, just bail out. Sounds not that nasty to > > me AFAIU. > > I don't see why we should have an S_ISREG() check. I agree it's not the > intended usecase, but it ought to work fine. Unless there's something > I'm missing? Check out this bug report: https://lore.kernel.org/lkml/CACkBjsYwLYLRmX8GpsDpMthagWOjWWrNxqY6ZLNQVr6yx+f5vA@mail.gmail.com/ and the patch from me: https://lore.kernel.org/linux-mm/20210917205731.262693-1-shy828301@gmail.com/ I don't think we handle buffers correctly for file THP, right? My patch is ad hoc, so I thought Hugh's suggestion makes some sense to me. Why do we have THP collapsed for unintended usecase in the first place?