On Wed, Jun 21, 2017 at 02:21:12PM -0700, Tahsin Erdogan wrote: > Setting a large xattr value may require writing the attribute contents > to an external inode. In this case we may need to lock the xattr inode > along with the parent inode. This doesn't pose a deadlock risk because > xattr inodes are not directly visible to the user and their access is > restricted. > > Assign a lockdep subclass to xattr inode's lock. > > ============================================ > WARNING: possible recursive locking detected > 4.12.0-rc1+ #740 Not tainted > -------------------------------------------- > python/1822 is trying to acquire lock: > (&sb->s_type->i_mutex_key#15){+.+...}, at: [<ffffffff804912ca>] ext4_xattr_set_entry+0x65a/0x7b0 > > but task is already holding lock: > (&sb->s_type->i_mutex_key#15){+.+...}, at: [<ffffffff803d6687>] vfs_setxattr+0x57/0xb0 > > other info that might help us debug this: > Possible unsafe locking scenario: > > CPU0 > ---- > lock(&sb->s_type->i_mutex_key#15); > lock(&sb->s_type->i_mutex_key#15); > > *** DEADLOCK *** > > May be due to missing lock nesting notation > > 4 locks held by python/1822: > #0: (sb_writers#10){.+.+.+}, at: [<ffffffff803d0eef>] mnt_want_write+0x1f/0x50 > #1: (&sb->s_type->i_mutex_key#15){+.+...}, at: [<ffffffff803d6687>] vfs_setxattr+0x57/0xb0 > #2: (jbd2_handle){.+.+..}, at: [<ffffffff80493f40>] start_this_handle+0xf0/0x420 > #3: (&ei->xattr_sem){++++..}, at: [<ffffffff804920ba>] ext4_xattr_set_handle+0x9a/0x4f0 > > stack backtrace: > CPU: 0 PID: 1822 Comm: python Not tainted 4.12.0-rc1+ #740 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > Call Trace: > dump_stack+0x67/0x9e > __lock_acquire+0x5f3/0x1750 > lock_acquire+0xb5/0x1d0 > down_write+0x2c/0x60 > ext4_xattr_set_entry+0x65a/0x7b0 > ext4_xattr_block_set+0x1b2/0x9b0 > ext4_xattr_set_handle+0x322/0x4f0 > ext4_xattr_set+0x144/0x1a0 > ext4_xattr_user_set+0x34/0x40 > __vfs_setxattr+0x66/0x80 > __vfs_setxattr_noperm+0x69/0x1c0 > vfs_setxattr+0xa2/0xb0 > setxattr+0x12e/0x150 > path_setxattr+0x87/0xb0 > SyS_setxattr+0xf/0x20 > entry_SYSCALL_64_fastpath+0x18/0xad > > Signed-off-by: Tahsin Erdogan <tahsin@xxxxxxxxxx> Thanks, applied. - Ted