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Date: Thu, 11 Feb 2021 11:22:25 +0100
From: Jan Kara <jack@...e.cz>
To: Hillf Danton <hdanton@...a.com>
Cc: syzbot <syzbot+a7ab8df042baaf42ae3c@...kaller.appspotmail.com>,
linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
syzkaller-bugs@...glegroups.com, Jan Kara <jack@...e.cz>,
Tahsin Erdogan <tahsin@...gle.com>, tytso@....edu
Subject: Re: possible deadlock in fs_reclaim_acquire (2)
On Thu 11-02-21 12:07:29, Hillf Danton wrote:
> On Wed, 10 Feb 2021 17:25:19 -0800
> > syzbot found the following issue on:
> >
> > HEAD commit: 825b5991 Merge tag '5.11-rc6-smb3' of git://git.samba.org/..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=117927bf500000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=bd1f72220b2e57eb
> > dashboard link: https://syzkaller.appspot.com/bug?extid=a7ab8df042baaf42ae3c
> > userspace arch: i386
> >
> > 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+a7ab8df042baaf42ae3c@...kaller.appspotmail.com
> >
> > ======================================================
> > WARNING: possible circular locking dependency detected
> > 5.11.0-rc6-syzkaller #0 Not tainted
> > ------------------------------------------------------
> > syz-executor.3/24553 is trying to acquire lock:
> > ffffffff8be892c0 (fs_reclaim){+.+.}-{0:0}, at: fs_reclaim_acquire+0xf7/0x150 mm/page_alloc.c:4348
> >
> > but task is already holding lock:
> > ffff888019b6b2c8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:142 [inline]
> > ffff888019b6b2c8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_xattr_set_handle+0x15c/0x13e0 fs/ext4/xattr.c:2308
> >
> > which lock already depends on the new lock.
> >
> >
> > the existing dependency chain (in reverse order) is:
> >
> > -> #3 (&ei->xattr_sem){++++}-{3:3}:
> > down_read+0x95/0x440 kernel/locking/rwsem.c:1353
> > ext4_setattr+0x570/0x1fd0 fs/ext4/inode.c:5375
> > notify_change+0xb60/0x10a0 fs/attr.c:336
> > chown_common+0x4a9/0x550 fs/open.c:674
> > vfs_fchown fs/open.c:741 [inline]
> > vfs_fchown fs/open.c:733 [inline]
> > ksys_fchown+0x111/0x170 fs/open.c:752
> > __do_sys_fchown fs/open.c:760 [inline]
> > __se_sys_fchown fs/open.c:758 [inline]
> > __x64_sys_fchown+0x6f/0xb0 fs/open.c:758
> > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
> > entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >
> > -> #2 (jbd2_handle){++++}-{0:0}:
> > start_this_handle+0xfb4/0x1380 fs/jbd2/transaction.c:446
> > jbd2__journal_start+0x399/0x930 fs/jbd2/transaction.c:503
> > __ext4_journal_start_sb+0x227/0x4a0 fs/ext4/ext4_jbd2.c:105
> > ext4_sample_last_mounted fs/ext4/file.c:804 [inline]
> > ext4_file_open+0x613/0xb40 fs/ext4/file.c:832
> > do_dentry_open+0x4b9/0x11b0 fs/open.c:817
> > do_open fs/namei.c:3254 [inline]
> > path_openat+0x1b9a/0x2730 fs/namei.c:3371
> > do_filp_open+0x17e/0x3c0 fs/namei.c:3398
> > do_open_execat+0x116/0x690 fs/exec.c:913
> > bprm_execve fs/exec.c:1801 [inline]
> > bprm_execve+0x4be/0x19a0 fs/exec.c:1788
> > do_execveat_common+0x626/0x7c0 fs/exec.c:1915
> > do_execve fs/exec.c:1983 [inline]
> > __do_sys_execve fs/exec.c:2059 [inline]
> > __se_sys_execve fs/exec.c:2054 [inline]
> > __x64_sys_execve+0x8f/0xc0 fs/exec.c:2054
> > do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
> > entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >
> > -> #1 (sb_internal){.+.+}-{0:0}:
> > percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
> > __sb_start_write include/linux/fs.h:1592 [inline]
> > sb_start_intwrite include/linux/fs.h:1709 [inline]
> > ext4_evict_inode+0xe6f/0x1940 fs/ext4/inode.c:241
> > evict+0x2ed/0x6b0 fs/inode.c:577
> > iput_final fs/inode.c:1653 [inline]
> > iput.part.0+0x57e/0x810 fs/inode.c:1679
> > iput fs/inode.c:1669 [inline]
> > inode_lru_isolate+0x301/0x4f0 fs/inode.c:778
> > __list_lru_walk_one+0x178/0x5c0 mm/list_lru.c:222
> > list_lru_walk_one+0x99/0xd0 mm/list_lru.c:266
> > list_lru_shrink_walk include/linux/list_lru.h:195 [inline]
> > prune_icache_sb+0xdc/0x140 fs/inode.c:803
> > super_cache_scan+0x38d/0x590 fs/super.c:107
> > do_shrink_slab+0x3e4/0x9f0 mm/vmscan.c:511
> > shrink_slab+0x16f/0x5d0 mm/vmscan.c:672
> > shrink_node_memcgs mm/vmscan.c:2665 [inline]
> > shrink_node+0x8cc/0x1de0 mm/vmscan.c:2780
> > kswapd_shrink_node mm/vmscan.c:3523 [inline]
> > balance_pgdat+0x745/0x1270 mm/vmscan.c:3681
> > kswapd+0x5b1/0xdb0 mm/vmscan.c:3938
> > kthread+0x3b1/0x4a0 kernel/kthread.c:292
> > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
> >
> > -> #0 (fs_reclaim){+.+.}-{0:0}:
> > check_prev_add kernel/locking/lockdep.c:2868 [inline]
> > check_prevs_add kernel/locking/lockdep.c:2993 [inline]
> > validate_chain kernel/locking/lockdep.c:3608 [inline]
> > __lock_acquire+0x2b26/0x54f0 kernel/locking/lockdep.c:4832
> > lock_acquire kernel/locking/lockdep.c:5442 [inline]
> > lock_acquire+0x1a8/0x720 kernel/locking/lockdep.c:5407
> > __fs_reclaim_acquire mm/page_alloc.c:4326 [inline]
> > fs_reclaim_acquire+0x117/0x150 mm/page_alloc.c:4340
> > might_alloc include/linux/sched/mm.h:193 [inline]
> > slab_pre_alloc_hook mm/slab.h:493 [inline]
> > slab_alloc_node mm/slub.c:2817 [inline]
> > __kmalloc_node+0x5f/0x430 mm/slub.c:4015
> > kmalloc_node include/linux/slab.h:575 [inline]
> > kvmalloc_node+0x61/0xf0 mm/util.c:587
> > kvmalloc include/linux/mm.h:781 [inline]
> > ext4_xattr_inode_cache_find fs/ext4/xattr.c:1465 [inline]
> > ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1508 [inline]
> > ext4_xattr_set_entry+0x1ce6/0x3780 fs/ext4/xattr.c:1649
> > ext4_xattr_ibody_set+0x78/0x2b0 fs/ext4/xattr.c:2224
> > ext4_xattr_set_handle+0x8f4/0x13e0 fs/ext4/xattr.c:2380
> > ext4_xattr_set+0x13a/0x340 fs/ext4/xattr.c:2493
> > ext4_xattr_user_set+0xbc/0x100 fs/ext4/xattr_user.c:40
> > __vfs_setxattr+0x10e/0x170 fs/xattr.c:177
> > __vfs_setxattr_noperm+0x11a/0x4c0 fs/xattr.c:208
> > __vfs_setxattr_locked+0x1bf/0x250 fs/xattr.c:266
> > vfs_setxattr+0x135/0x320 fs/xattr.c:291
> > setxattr+0x1ff/0x290 fs/xattr.c:553
> > path_setxattr+0x170/0x190 fs/xattr.c:572
> > __do_sys_setxattr fs/xattr.c:587 [inline]
> > __se_sys_setxattr fs/xattr.c:583 [inline]
> > __ia32_sys_setxattr+0xbc/0x150 fs/xattr.c:583
> > do_syscall_32_irqs_on arch/x86/entry/common.c:77 [inline]
> > __do_fast_syscall_32+0x56/0x80 arch/x86/entry/common.c:139
> > do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:164
> > entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
> >
> > other info that might help us debug this:
> >
> > Chain exists of:
> > fs_reclaim --> jbd2_handle --> &ei->xattr_sem
> >
> > Possible unsafe locking scenario:
> >
> > CPU0 CPU1
> > ---- ----
> > lock(&ei->xattr_sem);
> > lock(jbd2_handle);
> > lock(&ei->xattr_sem);
> > lock(fs_reclaim);
> >
> > *** DEADLOCK ***
> >
> > 3 locks held by syz-executor.3/24553:
> > #0: ffff888065bae460 (sb_writers#5){.+.+}-{0:0}, at: path_setxattr+0xb5/0x190 fs/xattr.c:570
> > #1: ffff888019b6b688 (&type->i_mutex_dir_key#4){++++}-{3:3}, at: inode_lock include/linux/fs.h:773 [inline]
> > #1: ffff888019b6b688 (&type->i_mutex_dir_key#4){++++}-{3:3}, at: vfs_setxattr+0x117/0x320 fs/xattr.c:290
> > #2: ffff888019b6b2c8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:142 [inline]
> > #2: ffff888019b6b2c8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_xattr_set_handle+0x15c/0x13e0 fs/ext4/xattr.c:2308
> >
> > stack backtrace:
> > CPU: 1 PID: 24553 Comm: syz-executor.3 Not tainted 5.11.0-rc6-syzkaller #0
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
> > Call Trace:
> > __dump_stack lib/dump_stack.c:79 [inline]
> > dump_stack+0x107/0x163 lib/dump_stack.c:120
> > check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2117
> > check_prev_add kernel/locking/lockdep.c:2868 [inline]
> > check_prevs_add kernel/locking/lockdep.c:2993 [inline]
> > validate_chain kernel/locking/lockdep.c:3608 [inline]
> > __lock_acquire+0x2b26/0x54f0 kernel/locking/lockdep.c:4832
> > lock_acquire kernel/locking/lockdep.c:5442 [inline]
> > lock_acquire+0x1a8/0x720 kernel/locking/lockdep.c:5407
> > __fs_reclaim_acquire mm/page_alloc.c:4326 [inline]
> > fs_reclaim_acquire+0x117/0x150 mm/page_alloc.c:4340
> > might_alloc include/linux/sched/mm.h:193 [inline]
> > slab_pre_alloc_hook mm/slab.h:493 [inline]
> > slab_alloc_node mm/slub.c:2817 [inline]
> > __kmalloc_node+0x5f/0x430 mm/slub.c:4015
> > kmalloc_node include/linux/slab.h:575 [inline]
> > kvmalloc_node+0x61/0xf0 mm/util.c:587
> > kvmalloc include/linux/mm.h:781 [inline]
> > ext4_xattr_inode_cache_find fs/ext4/xattr.c:1465 [inline]
> > ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1508 [inline]
> > ext4_xattr_set_entry+0x1ce6/0x3780 fs/ext4/xattr.c:1649
> > ext4_xattr_ibody_set+0x78/0x2b0 fs/ext4/xattr.c:2224
> > ext4_xattr_set_handle+0x8f4/0x13e0 fs/ext4/xattr.c:2380
> > ext4_xattr_set+0x13a/0x340 fs/ext4/xattr.c:2493
> > ext4_xattr_user_set+0xbc/0x100 fs/ext4/xattr_user.c:40
> > __vfs_setxattr+0x10e/0x170 fs/xattr.c:177
> > __vfs_setxattr_noperm+0x11a/0x4c0 fs/xattr.c:208
> > __vfs_setxattr_locked+0x1bf/0x250 fs/xattr.c:266
> > vfs_setxattr+0x135/0x320 fs/xattr.c:291
> > setxattr+0x1ff/0x290 fs/xattr.c:553
> > path_setxattr+0x170/0x190 fs/xattr.c:572
> > __do_sys_setxattr fs/xattr.c:587 [inline]
> > __se_sys_setxattr fs/xattr.c:583 [inline]
> > __ia32_sys_setxattr+0xbc/0x150 fs/xattr.c:583
> > do_syscall_32_irqs_on arch/x86/entry/common.c:77 [inline]
> > __do_fast_syscall_32+0x56/0x80 arch/x86/entry/common.c:139
> > do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:164
> > entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
>
> Fix 71b565ceff37 ("ext4: drop ext4_kvmalloc()") by restoring the
> GFP_NOFS introduced in dec214d00e0d ("ext4: xattr inode deduplication").
>
> Note this may be the fix also to possible deadlock
> Reported-by: syzbot+bfdded10ab7dcd7507ae@...kaller.appspotmail.com
> https://lore.kernel.org/linux-ext4/000000000000563a0205bafb7970@google.com/
Please no. Ext4 is using scoping API to limit allocations to GFP_NOFS
inside transactions. In this case something didn't work which seems like a
lockdep bug at the first sight but I'll talk to mm guys about it.
Definitely to problem doesn't seem to be in ext4.
Honza
>
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -1459,7 +1459,7 @@ ext4_xattr_inode_cache_find(struct inode
> if (!ce)
> return NULL;
>
> - ea_data = kvmalloc(value_len, GFP_KERNEL);
> + ea_data = kvmalloc(value_len, GFP_NOFS);
> if (!ea_data) {
> mb_cache_entry_put(ea_inode_cache, ce);
> return NULL;
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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