On Mon 24-04-23 01:11:37, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: e8d018dd0257 Linux 6.3-rc3 > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=13cd8a86c80000 > kernel config: https://syzkaller.appspot.com/x/.config?x=cde06fe2cf5765b7 > dashboard link: https://syzkaller.appspot.com/bug?extid=6898da502aef574c5f8a > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > > 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+6898da502aef574c5f8a@xxxxxxxxxxxxxxxxxxxxxxxxx > > ====================================================== > WARNING: possible circular locking dependency detected > 6.3.0-rc3-syzkaller #0 Not tainted > ------------------------------------------------------ > kswapd0/100 is trying to acquire lock: > ffff88801e636b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: do_writepages+0x1a8/0x640 mm/page-writeback.c:2551 > > but task is already holding lock: > ffffffff8c8e1280 (fs_reclaim){+.+.}-{0:0}, at: set_task_reclaim_state mm/vmscan.c:200 [inline] > ffffffff8c8e1280 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x170/0x1ac0 mm/vmscan.c:7338 > > which lock already depends on the new lock. This looks like a real deadlock opportunity in ext4 due to EXT4_SB(sb)->s_writepages_rwsem. The problem is like: CPU0 CPU1 ext4_writepages() percpu_down_read(sbi->s_writepages_rwsem); ext4_change_inode_journal_flag() percpu_down_write(sbi->s_writepages_rwsem); - blocks, all readers block from now on ext4_do_writepages() ext4_init_io_end() kmem_cache_zalloc(io_end_cachep, GFP_KERNEL) fs_reclaim frees dentry... dentry_unlink_inode() iput() - last ref => iput_final() - inode dirty => write_inode_now()... ext4_writepages() tries to acquire sbi->s_writepages_rwsem So we need to disable fs reclaim whenever we acquire s_writepages_rwsem. I'll send a patch. Honza > > the existing dependency chain (in reverse order) is: > > -> #1 (fs_reclaim){+.+.}-{0:0}: > __fs_reclaim_acquire mm/page_alloc.c:4716 [inline] > fs_reclaim_acquire+0x11d/0x160 mm/page_alloc.c:4730 > might_alloc include/linux/sched/mm.h:271 [inline] > slab_pre_alloc_hook mm/slab.h:728 [inline] > slab_alloc_node mm/slab.c:3241 [inline] > slab_alloc mm/slab.c:3266 [inline] > __kmem_cache_alloc_lru mm/slab.c:3443 [inline] > kmem_cache_alloc+0x3d/0x3f0 mm/slab.c:3452 > kmem_cache_zalloc include/linux/slab.h:710 [inline] > ext4_init_io_end+0x27/0x180 fs/ext4/page-io.c:278 > ext4_do_writepages+0xbea/0x31e0 fs/ext4/inode.c:2824 > ext4_writepages+0x27c/0x5e0 fs/ext4/inode.c:2964 > do_writepages+0x1a8/0x640 mm/page-writeback.c:2551 > __writeback_single_inode+0x121/0xdc0 fs/fs-writeback.c:1600 > writeback_sb_inodes+0x54d/0xe70 fs/fs-writeback.c:1891 > __writeback_inodes_wb+0xc6/0x280 fs/fs-writeback.c:1962 > wb_writeback+0x7e9/0xa50 fs/fs-writeback.c:2067 > wb_check_background_flush fs/fs-writeback.c:2133 [inline] > wb_do_writeback fs/fs-writeback.c:2221 [inline] > wb_workfn+0x8b0/0xfc0 fs/fs-writeback.c:2248 > process_one_work+0x991/0x15c0 kernel/workqueue.c:2390 > worker_thread+0x669/0x1090 kernel/workqueue.c:2537 > kthread+0x2e8/0x3a0 kernel/kthread.c:376 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308 > > -> #0 (&sbi->s_writepages_rwsem){++++}-{0:0}: > check_prev_add kernel/locking/lockdep.c:3098 [inline] > check_prevs_add kernel/locking/lockdep.c:3217 [inline] > validate_chain kernel/locking/lockdep.c:3832 [inline] > __lock_acquire+0x2ec7/0x5d40 kernel/locking/lockdep.c:5056 > lock_acquire kernel/locking/lockdep.c:5669 [inline] > lock_acquire+0x1af/0x520 kernel/locking/lockdep.c:5634 > percpu_down_read include/linux/percpu-rwsem.h:51 [inline] > ext4_writepages+0x1a9/0x5e0 fs/ext4/inode.c:2963 > do_writepages+0x1a8/0x640 mm/page-writeback.c:2551 > __writeback_single_inode+0x121/0xdc0 fs/fs-writeback.c:1600 > writeback_single_inode+0x2ad/0x590 fs/fs-writeback.c:1721 > write_inode_now+0x16e/0x1e0 fs/fs-writeback.c:2757 > iput_final fs/inode.c:1735 [inline] > iput.part.0+0x408/0x740 fs/inode.c:1774 > iput+0x5c/0x80 fs/inode.c:1764 > dentry_unlink_inode+0x2b1/0x460 fs/dcache.c:401 > __dentry_kill+0x3c0/0x640 fs/dcache.c:607 > shrink_dentry_list+0x12c/0x4f0 fs/dcache.c:1201 > prune_dcache_sb+0xeb/0x150 fs/dcache.c:1282 > super_cache_scan+0x33a/0x590 fs/super.c:104 > do_shrink_slab+0x428/0xaa0 mm/vmscan.c:853 > shrink_slab_memcg mm/vmscan.c:922 [inline] > shrink_slab+0x388/0x660 mm/vmscan.c:1001 > shrink_one+0x502/0x810 mm/vmscan.c:5343 > shrink_many mm/vmscan.c:5394 [inline] > lru_gen_shrink_node mm/vmscan.c:5511 [inline] > shrink_node+0x2064/0x35f0 mm/vmscan.c:6459 > kswapd_shrink_node mm/vmscan.c:7262 [inline] > balance_pgdat+0xa02/0x1ac0 mm/vmscan.c:7452 > kswapd+0x677/0xd60 mm/vmscan.c:7712 > kthread+0x2e8/0x3a0 kernel/kthread.c:376 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308 > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(fs_reclaim); > lock(&sbi->s_writepages_rwsem); > lock(fs_reclaim); > lock(&sbi->s_writepages_rwsem); > > *** DEADLOCK *** > > 3 locks held by kswapd0/100: > #0: ffffffff8c8e1280 (fs_reclaim){+.+.}-{0:0}, at: set_task_reclaim_state mm/vmscan.c:200 [inline] > #0: ffffffff8c8e1280 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x170/0x1ac0 mm/vmscan.c:7338 > #1: ffffffff8c8980b0 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab_memcg mm/vmscan.c:895 [inline] > #1: ffffffff8c8980b0 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x2a0/0x660 mm/vmscan.c:1001 > #2: ffff88801e6300e0 (&type->s_umount_key#50){++++}-{3:3}, at: trylock_super fs/super.c:414 [inline] > #2: ffff88801e6300e0 (&type->s_umount_key#50){++++}-{3:3}, at: super_cache_scan+0x70/0x590 fs/super.c:79 > > stack backtrace: > CPU: 1 PID: 100 Comm: kswapd0 Not tainted 6.3.0-rc3-syzkaller #0 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014 > Call Trace: > <TASK> > __dump_stack lib/dump_stack.c:88 [inline] > dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106 > check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2178 > check_prev_add kernel/locking/lockdep.c:3098 [inline] > check_prevs_add kernel/locking/lockdep.c:3217 [inline] > validate_chain kernel/locking/lockdep.c:3832 [inline] > __lock_acquire+0x2ec7/0x5d40 kernel/locking/lockdep.c:5056 > lock_acquire kernel/locking/lockdep.c:5669 [inline] > lock_acquire+0x1af/0x520 kernel/locking/lockdep.c:5634 > percpu_down_read include/linux/percpu-rwsem.h:51 [inline] > ext4_writepages+0x1a9/0x5e0 fs/ext4/inode.c:2963 > do_writepages+0x1a8/0x640 mm/page-writeback.c:2551 > __writeback_single_inode+0x121/0xdc0 fs/fs-writeback.c:1600 > writeback_single_inode+0x2ad/0x590 fs/fs-writeback.c:1721 > write_inode_now+0x16e/0x1e0 fs/fs-writeback.c:2757 > iput_final fs/inode.c:1735 [inline] > iput.part.0+0x408/0x740 fs/inode.c:1774 > iput+0x5c/0x80 fs/inode.c:1764 > dentry_unlink_inode+0x2b1/0x460 fs/dcache.c:401 > __dentry_kill+0x3c0/0x640 fs/dcache.c:607 > shrink_dentry_list+0x12c/0x4f0 fs/dcache.c:1201 > prune_dcache_sb+0xeb/0x150 fs/dcache.c:1282 > super_cache_scan+0x33a/0x590 fs/super.c:104 > do_shrink_slab+0x428/0xaa0 mm/vmscan.c:853 > shrink_slab_memcg mm/vmscan.c:922 [inline] > shrink_slab+0x388/0x660 mm/vmscan.c:1001 > shrink_one+0x502/0x810 mm/vmscan.c:5343 > shrink_many mm/vmscan.c:5394 [inline] > lru_gen_shrink_node mm/vmscan.c:5511 [inline] > shrink_node+0x2064/0x35f0 mm/vmscan.c:6459 > kswapd_shrink_node mm/vmscan.c:7262 [inline] > balance_pgdat+0xa02/0x1ac0 mm/vmscan.c:7452 > kswapd+0x677/0xd60 mm/vmscan.c:7712 > kthread+0x2e8/0x3a0 kernel/kthread.c:376 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308 > </TASK> > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 100 at fs/ext4/inode.c:5325 ext4_write_inode+0x337/0x590 fs/ext4/inode.c:5325 > Modules linked in: > CPU: 1 PID: 100 Comm: kswapd0 Not tainted 6.3.0-rc3-syzkaller #0 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014 > RIP: 0010:ext4_write_inode+0x337/0x590 fs/ext4/inode.c:5325 > Code: b6 04 02 84 c0 74 08 3c 03 0f 8e 3d 02 00 00 8b b5 b0 06 00 00 4c 89 f7 e8 c6 94 12 00 41 89 c4 e9 ed fd ff ff e8 e9 4e 5a ff <0f> 0b 45 31 e4 e9 de fd ff ff e8 da 4e 5a ff 48 89 ef 48 8d 74 24 > RSP: 0018:ffffc90000c87360 EFLAGS: 00010293 > RAX: 0000000000000000 RBX: 1ffff92000190e6c RCX: 0000000000000000 > RDX: ffff8880169700c0 RSI: ffffffff8227b6c7 RDI: 0000000000000005 > RBP: ffff8880283852f0 R08: 0000000000000005 R09: 0000000000000000 > R10: 0000000000000800 R11: 3e4b5341542f3c20 R12: 0000000000000800 > R13: ffffc90000c874e0 R14: dffffc0000000000 R15: ffff888028385318 > FS: 0000000000000000(0000) GS:ffff88802ca80000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fe7eabfe718 CR3: 00000000738f6000 CR4: 0000000000150ee0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > <TASK> > write_inode fs/fs-writeback.c:1453 [inline] > __writeback_single_inode+0x9f8/0xdc0 fs/fs-writeback.c:1665 > writeback_single_inode+0x2ad/0x590 fs/fs-writeback.c:1721 > write_inode_now+0x16e/0x1e0 fs/fs-writeback.c:2757 > iput_final fs/inode.c:1735 [inline] > iput.part.0+0x408/0x740 fs/inode.c:1774 > iput+0x5c/0x80 fs/inode.c:1764 > dentry_unlink_inode+0x2b1/0x460 fs/dcache.c:401 > __dentry_kill+0x3c0/0x640 fs/dcache.c:607 > shrink_dentry_list+0x12c/0x4f0 fs/dcache.c:1201 > prune_dcache_sb+0xeb/0x150 fs/dcache.c:1282 > super_cache_scan+0x33a/0x590 fs/super.c:104 > do_shrink_slab+0x428/0xaa0 mm/vmscan.c:853 > shrink_slab_memcg mm/vmscan.c:922 [inline] > shrink_slab+0x388/0x660 mm/vmscan.c:1001 > shrink_one+0x502/0x810 mm/vmscan.c:5343 > shrink_many mm/vmscan.c:5394 [inline] > lru_gen_shrink_node mm/vmscan.c:5511 [inline] > shrink_node+0x2064/0x35f0 mm/vmscan.c:6459 > kswapd_shrink_node mm/vmscan.c:7262 [inline] > balance_pgdat+0xa02/0x1ac0 mm/vmscan.c:7452 > kswapd+0x677/0xd60 mm/vmscan.c:7712 > kthread+0x2e8/0x3a0 kernel/kthread.c:376 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308 > </TASK> > > > --- > This report is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
