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[23.128.96.18]) by mx.google.com with ESMTP id h26si9845686ioz.60.2021.09.06.20.01.15; Mon, 06 Sep 2021 20:01:26 -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; 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=fail (p=NONE sp=NONE dis=NONE) header.from=alibaba.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235581AbhIGCuU (ORCPT + 99 others); Mon, 6 Sep 2021 22:50:20 -0400 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:54689 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230366AbhIGCuT (ORCPT ); Mon, 6 Sep 2021 22:50:19 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01424;MF=xuyu@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0UnYFK0M_1630982950; Received: from xuyu-mbp15.local(mailfrom:xuyu@linux.alibaba.com fp:SMTPD_---0UnYFK0M_1630982950) by smtp.aliyun-inc.com(127.0.0.1); Tue, 07 Sep 2021 10:49:11 +0800 Subject: Re: [PATCH 1/2] mm, thp: check page mapping when truncating page cache To: Rongwei Wang , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, cfijalkovich@google.com, song@kernel.org, william.kucharski@oracle.com, hughd@google.com References: <20210906121200.57905-1-rongwei.wang@linux.alibaba.com> <20210906121200.57905-2-rongwei.wang@linux.alibaba.com> From: Yu Xu Message-ID: Date: Tue, 7 Sep 2021 10:49:10 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20210906121200.57905-2-rongwei.wang@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/6/21 8:11 PM, 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:0000000000000000 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 dead000000000400 > [40326.247053] raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000 > [40326.247055] head: 37fffe0000010815 fffffe001066bd48 ffff000404183c20 0000000000000000 > [40326.247057] head: 0000000000000600 0000000000000000 00000001ffffffff ffff000c0345a000 > [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_blk(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) virtio(E) > [40326.285130] CPU: 14 PID: 11394 Comm: check_madvise_d Kdump: loaded Tainted: 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=--) > [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 *mapping, pgoff_t start, > if (!xa_is_value(page)) { > if (page->index < start) > goto put; > - VM_BUG_ON_PAGE(page->index != xas.xa_index, page); > 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 *mapping, 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 already > + * be truncated with page->mapping reset to NULL. > + */ > + VM_BUG_ON_PAGE(page->index != xas.xa_index, page); > } > indices[pvec->nr] = 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 = start; > while (index < end && find_lock_entries(mapping, index, end - 1, > &pvec, indices)) { > - index = indices[pagevec_count(&pvec) - 1] + 1; > + index = indices[pagevec_count(&pvec) - 1] + > + thp_nr_pages(pvec.pages[pagevec_count(&pvec) - 1]); > truncate_exceptional_pvec_entries(mapping, &pvec, indices); > for (i = 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 truncated. > + * > + * In addition, another race will be avoided, where > + * collapse_file rolls back when writer truncates the > + * page cache. > + */ > + if (page_mapping(page) != mapping) { > + /* Restart to make sure all gone */ > + index = start - 1; > + continue; > + } > + > lock_page(page); Better to check page mapping with page lock, i.e., move above chunk after lock_page(page), and do not forget to unlock. lock_page(page); + /* + * Already truncated? We can find and get subpage + * of file THP, of which the head page is truncated. + * + * In addition, another race will be avoided, where + * collapse_file rolls back when writer truncates the + * page cache. + */ + if (page_mapping(page) != mapping) { + unlock_page(page); + /* Restart to make sure all gone */ + index = start - 1; + break; + } + We will wait for other reviews till we send out v2. > WARN_ON(page_to_index(page) != index); > wait_on_page_writeback(page); > -- Thanks, Yu