21ad2d0364
xfs/399 found the following deadlock when fuzzing core.mode = ones: /proc/20506/task/20558/stack : [<0>] xfs_ilock+0xa0/0x240 [xfs] [<0>] xfs_ilock_data_map_shared+0x1b/0x20 [xfs] [<0>] xrep_dinode_findmode_walk_directory+0x69/0xe0 [xfs] [<0>] xrep_dinode_find_mode+0x103/0x2a0 [xfs] [<0>] xrep_dinode_mode+0x7c/0x120 [xfs] [<0>] xrep_dinode_core+0xed/0x2b0 [xfs] [<0>] xrep_dinode_problems+0x10/0x80 [xfs] [<0>] xrep_inode+0x6c/0xc0 [xfs] [<0>] xrep_attempt+0x64/0x1d0 [xfs] [<0>] xfs_scrub_metadata+0x365/0x840 [xfs] [<0>] xfs_scrubv_metadata+0x282/0x430 [xfs] [<0>] xfs_ioc_scrubv_metadata+0x149/0x1a0 [xfs] [<0>] xfs_file_ioctl+0xc68/0x1780 [xfs] /proc/20506/task/20559/stack : [<0>] xfs_buf_lock+0x3b/0x110 [xfs] [<0>] xfs_buf_find_lock+0x66/0x1c0 [xfs] [<0>] xfs_buf_get_map+0x208/0xc00 [xfs] [<0>] xfs_buf_read_map+0x5d/0x2c0 [xfs] [<0>] xfs_trans_read_buf_map+0x1b0/0x4c0 [xfs] [<0>] xfs_read_agi+0xbd/0x190 [xfs] [<0>] xfs_ialloc_read_agi+0x47/0x160 [xfs] [<0>] xfs_imap_lookup+0x69/0x1f0 [xfs] [<0>] xfs_imap+0x1fc/0x3d0 [xfs] [<0>] xfs_iget+0x357/0xd50 [xfs] [<0>] xchk_dir_actor+0x16e/0x330 [xfs] [<0>] xchk_dir_walk_block+0x164/0x1e0 [xfs] [<0>] xchk_dir_walk+0x13a/0x190 [xfs] [<0>] xchk_directory+0x1a2/0x2b0 [xfs] [<0>] xfs_scrub_metadata+0x2f4/0x840 [xfs] [<0>] xfs_scrubv_metadata+0x282/0x430 [xfs] [<0>] xfs_ioc_scrubv_metadata+0x149/0x1a0 [xfs] [<0>] xfs_file_ioctl+0xc68/0x1780 [xfs] Thread 20558 holds an AGI buffer and is trying to grab the ILOCK of the root directory. Thread 20559 holds the root directory ILOCK and is trying to grab the AGI of an inode that is one of the root directory's children. The AGI held by 20558 is the same buffer that 20559 is trying to acquire. In other words, this is an ABBA deadlock. In general, the lock order is ILOCK and then AGI -- rename does this while preparing for an operation involving whiteouts or renaming files out of existence; and unlink does this when moving an inode to the unlinked list. The only place where we do it in the opposite order is on the child during an icreate, but at that point the child is marked INEW and is not visible to other threads. Work around this deadlock by replacing the blocking ilock attempt with a nonblocking loop that aborts after 30 seconds. Relax for a jiffy after a failed lock attempt. Signed-off-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.