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9e769bd7e5
In production we hit the following deadlock
task 1 task 2 task 3
------ ------ ------
fiemap(file) falloc(file) fsync(file)
write(0, 1MiB)
btrfs_commit_transaction()
wait_on(!pending_ordered)
lock(512MiB, 1GiB)
start_transaction
wait_on_transaction
lock(0, 1GiB)
wait_extent_bit(512MiB)
task 4
------
finish_ordered_extent(0, 1MiB)
lock(0, 1MiB)
**DEADLOCK**
This occurs because when task 1 does it's lock, it locks everything from
0-512MiB, and then waits for the 512MiB chunk to unlock. task 2 will
never unlock because it's waiting on the transaction commit to happen,
the transaction commit is waiting for the outstanding ordered extents,
and then the ordered extent thread is blocked waiting on the 0-1MiB
range to unlock.
To fix this we have to clear anything we've locked so far, wait for the
extent_state that we contended on, and then try to re-lock the entire
range again.
CC: stable@vger.kernel.org # 5.15+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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 Restructured Text 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.