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From: Naoya Horiguchi To: Christoph Hellwig Cc: Andrew Morton , Matthew Wilcox , Hugh Dickins , linux-afs@lists.infradead.org, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, cluster-devel@redhat.com, linux-mm@kvack.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nilfs@vger.kernel.org, naoya.horiguchi@nec.com Subject: Re: [PATCH 7/7] mm: return an ERR_PTR from __filemap_get_folio Message-ID: <20230310043137.GA1624890@u2004> References: <20230121065755.1140136-1-hch@lst.de> <20230121065755.1140136-8-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230121065755.1140136-8-hch@lst.de> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 8B63D180005 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: ieqp7k894amafpnpgjpau8a6ih6qgasb X-HE-Tag: 1678422709-2130 X-HE-Meta: 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 dyUZMf99 naF2ND4Y3Ta2u2kU2mZ6tU02Y2dEP4/stU2PrCNP2B5OPiWPofF9OcLmAxBRIFIfUQT9dPVHSU2nnhHD2/z5fBc2cMIX2YH1WV3TxuqEFI+Cx4dK3yyXIDZ8mrfwWK2h83lcjedlB2cDc5uSioipubZRlRg== 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, Jan 21, 2023 at 07:57:55AM +0100, Christoph Hellwig wrote: > Instead of returning NULL for all errors, distinguish between: > > - no entry found and not asked to allocated (-ENOENT) > - failed to allocate memory (-ENOMEM) > - would block (-EAGAIN) > > so that callers don't have to guess the error based on the passed > in flags. > > Also pass through the error through the direct callers: > filemap_get_folio, filemap_lock_folio filemap_grab_folio > and filemap_get_incore_folio. > > Signed-off-by: Christoph Hellwig Hello, I found a NULL pointer dereference issue related to this patch, so let me share it. Here is the bug message (I used akpm/mm-unstable on Mar 9): [ 2871.648659] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 2871.651286] #PF: supervisor read access in kernel mode [ 2871.653231] #PF: error_code(0x0000) - not-present page [ 2871.655170] PGD 80000001517dd067 P4D 80000001517dd067 PUD 1491d1067 PMD 0 [ 2871.657739] Oops: 0000 [#1] PREEMPT SMP PTI [ 2871.659329] CPU: 4 PID: 1599 Comm: page-types Tainted: G E N 6.3.0-rc1-v6.3-rc1-230309-1629-189-ga71a7+ #36 [ 2871.663362] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014 [ 2871.666507] RIP: 0010:mincore_page+0x19/0x90 [ 2871.668086] Code: cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 41 54 55 53 e8 92 2b 03 00 48 3d 00 f0 ff ff 77 54 48 89 c3 <48> 8b 00 48 c1 e8 02 89 c5 83 e5 01 75 21 8b 43 34 85 c0 74 47 f0 [ 2871.678313] RSP: 0018:ffffbe57c203fd00 EFLAGS: 00010207 [ 2871.681422] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 2871.685609] RDX: 0000000000000000 RSI: ffff9f59ca1506d8 RDI: ffff9f59ce7c2880 [ 2871.689599] RBP: 0000000000000000 R08: 00007f9f14200000 R09: ffff9f59c9078508 [ 2871.693295] R10: 00007f9ed4400000 R11: 0000000000000000 R12: 0000000000000200 [ 2871.695969] R13: 0000000000000001 R14: ffff9f59c9ef4450 R15: ffff9f59c4ac9000 [ 2871.699927] FS: 00007f9ed47ee740(0000) GS:ffff9f5abbc00000(0000) knlGS:0000000000000000 [ 2871.703969] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 2871.706689] CR2: 0000000000000000 CR3: 0000000149ffe006 CR4: 0000000000170ee0 [ 2871.709923] DR0: ffffffff91531760 DR1: ffffffff91531761 DR2: ffffffff91531762 [ 2871.713424] DR3: ffffffff91531763 DR6: 00000000ffff0ff0 DR7: 0000000000000600 [ 2871.716758] Call Trace: [ 2871.717998] [ 2871.719008] __mincore_unmapped_range+0x6e/0xd0 [ 2871.721220] mincore_unmapped_range+0x16/0x30 [ 2871.723288] walk_pgd_range+0x485/0x9e0 [ 2871.725128] __walk_page_range+0x195/0x1b0 [ 2871.727224] walk_page_range+0x151/0x180 [ 2871.728883] __do_sys_mincore+0xec/0x2b0 [ 2871.730707] do_syscall_64+0x3a/0x90 [ 2871.732179] entry_SYSCALL_64_after_hwframe+0x72/0xdc [ 2871.734148] RIP: 0033:0x7f9ed443f4ab [ 2871.735548] Code: 73 01 c3 48 8b 0d 75 99 1b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 1b 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 45 99 1b 00 f7 d8 64 89 01 48 [ 2871.742194] RSP: 002b:00007ffe924d72b8 EFLAGS: 00000206 ORIG_RAX: 000000000000001b [ 2871.744787] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f9ed443f4ab [ 2871.747186] RDX: 00007ffe92557300 RSI: 0000000000200000 RDI: 00007f9ed4200000 [ 2871.749404] RBP: 00007ffe92567330 R08: 0000000000000005 R09: 0000000000000000 [ 2871.751683] R10: 00007f9ed4405d68 R11: 0000000000000206 R12: 00007ffe925674b8 [ 2871.753925] R13: 0000000000404af1 R14: 000000000040ad78 R15: 00007f9ed4833000 [ 2871.756493] The precedure to reproduce this is (1) punch hole some page in a shmem file, then (2) call mincore() over the punch-holed address range. I confirmed that filemap_get_incore_folio() (actually filemap_get_entry() inside it) returns NULL in that case, so we unexpectedly enter the following if-block for the "not found" case. > diff --git a/mm/mincore.c b/mm/mincore.c > index cd69b9db008126..5437e584b208bf 100644 > --- a/mm/mincore.c > +++ b/mm/mincore.c > @@ -61,7 +61,7 @@ static unsigned char mincore_page(struct address_space *mapping, pgoff_t index) > * tmpfs's .fault). So swapped out tmpfs mappings are tested here. > */ > folio = filemap_get_incore_folio(mapping, index); > - if (folio) { > + if (!IS_ERR(folio)) { > present = folio_test_uptodate(folio); > folio_put(folio); > } I guess that this patch intends to make filemap_get_incore_folio() return non-NULL error code, so replacing the check with "if (!IS_ERR_OR_NULL(folio))" cannot be a solution. But I have no idea about the fix, so could you help me? Thanks, Naoya Horiguchi