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[23.128.96.18]) by mx.google.com with ESMTP id h1si428968edv.341.2021.09.08.14.50.33; Wed, 08 Sep 2021 14:50:56 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20210112 header.b=Csehjym8; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234144AbhIHVtc (ORCPT + 99 others); Wed, 8 Sep 2021 17:49:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231639AbhIHVta (ORCPT ); Wed, 8 Sep 2021 17:49:30 -0400 Received: from mail-ej1-x62f.google.com (mail-ej1-x62f.google.com [IPv6:2a00:1450:4864:20::62f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E51C7C061575 for ; Wed, 8 Sep 2021 14:48:21 -0700 (PDT) Received: by mail-ej1-x62f.google.com with SMTP id jg16so7099468ejc.1 for ; Wed, 08 Sep 2021 14:48:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=0yNuiTKESTFJZYHvoKNI0e3rHjuRq3rggt+cKvIaRL0=; b=Csehjym8zU4lWEXymsRB65Up2LNrIqbKIAcYOaghmA+JTST600+hySk8ViX6rkngFC slztu4bQRVZI8mqU1mRoYmC/6gKy9g5eEJ0yKlqJPRPgLSLVyiUgLU3Tv3DPpDK/FvHw lLo5ONNCURy8JazgsuzmDEN0jA3SGBDsI6RAeSil7Fa6QlevCu0GkCRgT7GLudXM0ObR mIHG/1GBOabPfdEUbaQp8IuQzL77fuJ8EyZ2jucfUrVspZ98ZzMg9i+F3b46yh29SuaW qX4bE5/24K+VRK+OPwL4CmBy5/zXDrrT2Bcm5mMXKszyw6Dns8r041yyAQnPiYLr/IXw 7cVQ== X-Google-DKIM-Signature: v=1; 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:content-transfer-encoding; bh=0yNuiTKESTFJZYHvoKNI0e3rHjuRq3rggt+cKvIaRL0=; b=PuM+W0fwwjU3Av0T/dRqagPhAeoE6bnW4JMMOKAdUcemSaJy36RSUVTf5G6+NaiitO J9dGoeyRzVztBRG4Uoghwcj+0BsIE2nQIrXgeliee3wq1J79MuJntZGEelZgS9Gq1sAa TV1QlU0hZ50F4pQjoj+UnsJpQPRWfSswy27UEDTED63BvrT44ERbMuLKwJyoVTJL/FYa KStUUz+a8Vyb/4km9esvfK5Zs1OW/W4L1bUp8eZmvMKmIPK6tehRXLqgnvO7cCxvht7I Bpp1Hq0nI1GvgRWZNmjR+kDPdR6i9yUfpEHA7JvyEgy3dDZp9B0DhB8EMTHiO35fJZ7P Uu7w== X-Gm-Message-State: AOAM532HSf7mEWinSWzLC3QrhkjZ17QNeZ1o8Q83uantRv431xNOt16L oDOqTZImOD2+ZKliWTOjAT78kC4FXguaaoVv/yUJFaSd X-Received: by 2002:a17:907:6297:: with SMTP id nd23mr269433ejc.62.1631137700381; Wed, 08 Sep 2021 14:48:20 -0700 (PDT) MIME-Version: 1.0 References: <20210906121200.57905-1-rongwei.wang@linux.alibaba.com> <20210906121200.57905-2-rongwei.wang@linux.alibaba.com> <38AF4DC8-5E6F-4568-B2E3-0434BD847BC9@linux.alibaba.com> In-Reply-To: <38AF4DC8-5E6F-4568-B2E3-0434BD847BC9@linux.alibaba.com> From: Yang Shi Date: Wed, 8 Sep 2021 14:48:08 -0700 Message-ID: Subject: Re: [PATCH 1/2] mm, thp: check page mapping when truncating page cache To: Rongwei Wang Cc: Linux MM , Linux Kernel Mailing List , Andrew Morton , cfijalkovich@google.com, song@kernel.org, william.kucharski@oracle.com, Hugh Dickins , Matthew Wilcox Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 7, 2021 at 7:41 PM Rongwei Wang wrote: > > > > On Sep 8, 2021, at 2:08 AM, Yang Shi wrote: > > On Mon, Sep 6, 2021 at 5:12 AM Rongwei Wang > wrote: > > > Transparent huge page has supported read-only non-shmem files. The file- > backed THP is collapsed by khugepaged and truncated when written (for > shared libraries). > > However, there is race in two possible places. > > 1) multiple writers truncate the same page cache concurrently; > 2) collapse_file rolls back when writer truncates the page cache; > > In both cases, subpage(s) of file THP can be revealed by find_get_entry > in truncate_inode_pages_range, which will trigger PageTail BUG_ON in > truncate_inode_page, as follows. > > [40326.247034] page:000000009e420ff2 refcount:1 mapcount:0 mapping:000000= 0000000000 index:0x7ff pfn:0x50c3ff > [40326.247041] head:0000000075ff816d order:9 compound_mapcount:0 compound= _pincount:0 > [40326.247046] flags: 0x37fffe0000010815(locked|uptodate|lru|arch_1|head) > [40326.247051] raw: 37fffe0000000000 fffffe0013108001 dead000000000122 de= ad000000000400 > [40326.247053] raw: 0000000000000001 0000000000000000 00000000ffffffff 00= 00000000000000 > [40326.247055] head: 37fffe0000010815 fffffe001066bd48 ffff000404183c20 0= 000000000000000 > [40326.247057] head: 0000000000000600 0000000000000000 00000001ffffffff f= fff000c0345a000 > [40326.247058] page dumped because: VM_BUG_ON_PAGE(PageTail(page)) > [40326.247077] ------------[ cut here ]------------ > [40326.247080] kernel BUG at mm/truncate.c:213! > [40326.280581] Internal error: Oops - BUG: 0 [#1] SMP > [40326.281077] Modules linked in: xfs(E) libcrc32c(E) rfkill(E) aes_ce_bl= k(E) crypto_simd(E) cryptd(E) aes_ce_cipher(E) crct10dif_ce(E) ghash_ce(E) = sha1_ce(E) uio_pdrv_genirq(E) uio(E) nfsd(E) vfat(E) fat(E) auth_rpcgss(E) = nfs_acl(E) lockd(E) grace(E) sunrpc(E) sch_fq_codel(E) ip_tables(E) ext4(E)= mbcache(E) jbd2(E) virtio_net(E) net_failover(E) virtio_blk(E) failover(E)= sha2_ce(E) sha256_arm64(E) virtio_mmio(E) virtio_pci(E) virtio_ring(E) vir= tio(E) > [40326.285130] CPU: 14 PID: 11394 Comm: check_madvise_d Kdump: loaded Tai= nted: G W E 5.10.46-hugetext+ #55 > [40326.286202] Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS 0.0.0= 02/06/2015 > [40326.286968] pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=3D--) > [40326.287584] pc : truncate_inode_page+0x64/0x70 > [40326.288040] lr : truncate_inode_page+0x64/0x70 > [40326.288498] sp : ffff80001b60b900 > [40326.288837] x29: ffff80001b60b900 x28: 00000000000007ff > [40326.289377] x27: ffff80001b60b9a0 x26: 0000000000000000 > [40326.289943] x25: 000000000000000f x24: ffff80001b60b9a0 > [40326.290485] x23: ffff80001b60ba18 x22: ffff0001e0999ea8 > [40326.291027] x21: ffff0000c21db300 x20: ffffffffffffffff > [40326.291566] x19: fffffe001310ffc0 x18: 0000000000000020 > [40326.292106] x17: 0000000000000000 x16: 0000000000000000 > [40326.292655] x15: ffff0000c21db960 x14: 3030306666666620 > [40326.293197] x13: 6666666666666666 x12: 3130303030303030 > [40326.293746] x11: ffff8000117b69b8 x10: 00000000ffff8000 > [40326.294313] x9 : ffff80001012690c x8 : 0000000000000000 > [40326.294851] x7 : ffff8000114f69b8 x6 : 0000000000017ffd > [40326.295392] x5 : ffff0007fffbcbc8 x4 : ffff80001b60b5c0 > [40326.295942] x3 : 0000000000000001 x2 : 0000000000000000 > [40326.296497] x1 : 0000000000000000 x0 : 0000000000000000 > [40326.297047] Call trace: > [40326.297304] truncate_inode_page+0x64/0x70 > [40326.297724] truncate_inode_pages_range+0x550/0x7e4 > [40326.298251] truncate_pagecache+0x58/0x80 > [40326.298662] do_dentry_open+0x1e4/0x3c0 > [40326.299052] vfs_open+0x38/0x44 > [40326.299377] do_open+0x1f0/0x310 > [40326.299709] path_openat+0x114/0x1dc > [40326.300077] do_filp_open+0x84/0x134 > [40326.300444] do_sys_openat2+0xbc/0x164 > [40326.300825] __arm64_sys_openat+0x74/0xc0 > [40326.301236] el0_svc_common.constprop.0+0x88/0x220 > [40326.301723] do_el0_svc+0x30/0xa0 > [40326.302089] el0_svc+0x20/0x30 > [40326.302404] el0_sync_handler+0x1a4/0x1b0 > [40326.302814] el0_sync+0x180/0x1c0 > [40326.303157] Code: aa0103e0 900061e1 910ec021 9400d300 (d4210000) > [40326.303775] ---[ end trace f70cdb42cb7c2d42 ]--- > [40326.304244] Kernel panic - not syncing: Oops - BUG: Fatal exception > > This checks the page mapping and retries when subpage of file THP is > found, in truncate_inode_pages_range. > > Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on file-= backed THPs") > Signed-off-by: Xu Yu > Signed-off-by: Rongwei Wang > --- > mm/filemap.c | 7 ++++++- > mm/truncate.c | 17 ++++++++++++++++- > 2 files changed, 22 insertions(+), 2 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index dae481293..a3af2ec 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2093,7 +2093,6 @@ unsigned find_lock_entries(struct address_space *ma= pping, pgoff_t start, > if (!xa_is_value(page)) { > if (page->index < start) > goto put; > - VM_BUG_ON_PAGE(page->index !=3D xas.xa_index, pag= e); > if (page->index + thp_nr_pages(page) - 1 > end) > goto put; > if (!trylock_page(page)) > @@ -2102,6 +2101,12 @@ unsigned find_lock_entries(struct address_space *m= apping, pgoff_t start, > goto unlock; > VM_BUG_ON_PAGE(!thp_contains(page, xas.xa_index), > page); > + /* > + * We can find and get head page of file THP with > + * non-head index. The head page should have alre= ady > + * be truncated with page->mapping reset to NULL. > + */ > + VM_BUG_ON_PAGE(page->index !=3D xas.xa_index, pag= e); > } > indices[pvec->nr] =3D xas.xa_index; > if (!pagevec_add(pvec, page)) > diff --git a/mm/truncate.c b/mm/truncate.c > index 714eaf1..8c59c00 100644 > --- a/mm/truncate.c > +++ b/mm/truncate.c > @@ -319,7 +319,8 @@ void truncate_inode_pages_range(struct address_space = *mapping, > index =3D start; > while (index < end && find_lock_entries(mapping, index, end - 1, > &pvec, indices)) { > - index =3D indices[pagevec_count(&pvec) - 1] + 1; > + index =3D indices[pagevec_count(&pvec) - 1] + > + thp_nr_pages(pvec.pages[pagevec_count(&pvec) - 1]= ); > > > I don't quite get what this change is doing for. IIUC > find_lock_entries() already handles index advance correctly. If > truncate range is partial THP, it will be handled in the second pass. > > Yes, agree. > > AFAICT, the problem is why the THP is not split if it will get > > Yes, agree. > > This change is not necessary, but nice to have. Because find_lock_entries= () > return only head page if any, and it is better to advance the index by th= p_nr_pages(), instead of 1. > > If you think it introduces unnecessary complexity, I don't mind discardin= g this change. IIUC this change may reduce some runtime overhead (-1 call to find_lock_entries()), but I'd suggest you wait for the comments from Matthew. > > partially truncated. Did I miss something? > > > > truncate_exceptional_pvec_entries(mapping, &pvec, indices)= ; > for (i =3D 0; i < pagevec_count(&pvec); i++) > truncate_cleanup_page(pvec.pages[i]); > @@ -391,6 +392,20 @@ void truncate_inode_pages_range(struct address_space= *mapping, > if (xa_is_value(page)) > continue; > > + /* > + * Already truncated? We can find and get subpage > + * of file THP, of which the head page is truncat= ed. > + * > + * In addition, another race will be avoided, whe= re > + * collapse_file rolls back when writer truncates= the > + * page cache. > + */ > + if (page_mapping(page) !=3D mapping) { > + /* Restart to make sure all gone */ > + index =3D start - 1; > + continue; > + } > + > lock_page(page); > WARN_ON(page_to_index(page) !=3D index); > wait_on_page_writeback(page); > =E2=80=94 > 1.8.3.1 > > Thanks, > Rongwei Wang >