On Sun, 03 Jan 2021 06:19:15 -0800 syzbot <syzbot+2fc0712f8f8b8b8fa0ef@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 139711f0 Merge branch 'akpm' (patches from Andrew) > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=11648e93500000 > kernel config: https://syzkaller.appspot.com/x/.config?x=f3e74a3fb99ae2c2 > dashboard link: https://syzkaller.appspot.com/bug?extid=2fc0712f8f8b8b8fa0ef > compiler: gcc (GCC) 10.1.0-syz 20200507 > > Unfortunately, I don't have any reproducer for this issue yet. > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+2fc0712f8f8b8b8fa0ef@xxxxxxxxxxxxxxxxxxxxxxxxx > > kernel BUG at mm/page-writeback.c:2241! > invalid opcode: 0000 [#1] PREEMPT SMP KASAN > CPU: 1 PID: 26311 Comm: syz-executor.2 Not tainted 5.11.0-rc1-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > RIP: 0010:write_cache_pages+0xd06/0x1190 mm/page-writeback.c:2241 > Code: 02 00 00 e8 dc 6e da ff 48 c7 c6 80 64 54 89 4c 89 ef e8 0d 04 0b 00 0f 0b 49 c7 c4 c0 77 f7 8e e9 ce f9 ff ff e8 ba 6e da ff <0f> 0b e8 b3 6e da ff 49 8d 5c 24 ff e9 c5 f8 ff ff e8 a4 6e da ff > RSP: 0018:ffffc9000931f850 EFLAGS: 00010212 > RAX: 000000000000ac05 RBX: 0000000000008000 RCX: ffffc9000d7c1000 > RDX: 0000000000040000 RSI: ffffffff819805d6 RDI: 0000000000000003 > RBP: 0000000000000000 R08: 0000000000000000 R09: ffffea0000c0ce07 > R10: ffffffff8197fee3 R11: 0000000000000000 R12: ffffea0002762cc8 > R13: ffffea0000c0ce00 R14: dffffc0000000000 R15: 0000000000000000 > FS: 00007f653a526700(0000) GS:ffff8880b9f00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 000000000052e94c CR3: 0000000015251000 CR4: 0000000000350ee0 > Call Trace: > mpage_writepages+0xd8/0x230 fs/mpage.c:714 > do_writepages+0xec/0x290 mm/page-writeback.c:2352 > __filemap_fdatawrite_range+0x2a1/0x380 mm/filemap.c:422 > fat_cont_expand+0x169/0x230 fs/fat/file.c:235 > fat_setattr+0xac2/0xf40 fs/fat/file.c:501 > notify_change+0xb60/0x10a0 fs/attr.c:336 > do_truncate+0x134/0x1f0 fs/open.c:64 > do_sys_ftruncate+0x703/0x860 fs/open.c:195 > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > RIP: 0033:0x45e299 > Code: 0d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 db b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007f653a525c68 EFLAGS: 00000246 ORIG_RAX: 000000000000004d > RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 000000000045e299 > RDX: 0000000000000000 RSI: 0000000000000800 RDI: 0000000000000003 > RBP: 000000000119c060 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 000000000119c034 > R13: 00007fff76bf2e8f R14: 00007f653a5269c0 R15: 000000000119c034 > Modules linked in: > ---[ end trace 23c7a881902c6de9 ]--- > RIP: 0010:write_cache_pages+0xd06/0x1190 mm/page-writeback.c:2241 > Code: 02 00 00 e8 dc 6e da ff 48 c7 c6 80 64 54 89 4c 89 ef e8 0d 04 0b 00 0f 0b 49 c7 c4 c0 77 f7 8e e9 ce f9 ff ff e8 ba 6e da ff <0f> 0b e8 b3 6e da ff 49 8d 5c 24 ff e9 c5 f8 ff ff e8 a4 6e da ff > RSP: 0018:ffffc9000931f850 EFLAGS: 00010212 > RAX: 000000000000ac05 RBX: 0000000000008000 RCX: ffffc9000d7c1000 > RDX: 0000000000040000 RSI: ffffffff819805d6 RDI: 0000000000000003 > RBP: 0000000000000000 R08: 0000000000000000 R09: ffffea0000c0ce07 > R10: ffffffff8197fee3 R11: 0000000000000000 R12: ffffea0002762cc8 > R13: ffffea0000c0ce00 R14: dffffc0000000000 R15: 0000000000000000 > FS: 00007f653a526700(0000) GS:ffff8880b9f00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000001b2f228000 CR3: 0000000015251000 CR4: 0000000000350ee0 Well that's exciting. write_cache_pages() does: if (PageWriteback(page)) { if (wbc->sync_mode != WB_SYNC_NONE) wait_on_page_writeback(page); else goto continue_unlock; } bang -->> BUG_ON(PageWriteback(page)); and filemap_fdatawrite_range() passed WB_SYNC_ALL to __filemap_fdatawrite_range(). So either wait_on_page_writeback() simply failed to work (returned without waiting) or someone came in and unexpectedly set PG_writeback a second time. And because it isn't reproducible, we don't know if it's a -mm patch or it it's a mainline bug or whatever. There isn't much material in -mm at present and I can't see any which would affect these things, so is it reasonable to suspect that this is a mainline bug? Linus, how confident are you in those wait_on_page_bit_common() changes?
