dbd0f52993
AIL flushing can get stuck here: [316649.005769] INFO: task xfsaild/pmem1:324525 blocked for more than 123 seconds. [316649.007807] Not tainted 5.17.0-rc6-dgc+ #975 [316649.009186] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [316649.011720] task:xfsaild/pmem1 state:D stack:14544 pid:324525 ppid: 2 flags:0x00004000 [316649.014112] Call Trace: [316649.014841] <TASK> [316649.015492] __schedule+0x30d/0x9e0 [316649.017745] schedule+0x55/0xd0 [316649.018681] io_schedule+0x4b/0x80 [316649.019683] xfs_buf_wait_unpin+0x9e/0xf0 [316649.021850] __xfs_buf_submit+0x14a/0x230 [316649.023033] xfs_buf_delwri_submit_buffers+0x107/0x280 [316649.024511] xfs_buf_delwri_submit_nowait+0x10/0x20 [316649.025931] xfsaild+0x27e/0x9d0 [316649.028283] kthread+0xf6/0x120 [316649.030602] ret_from_fork+0x1f/0x30 in the situation where flushing gets preempted between the unpin check and the buffer trylock under nowait conditions: blk_start_plug(&plug); list_for_each_entry_safe(bp, n, buffer_list, b_list) { if (!wait_list) { if (xfs_buf_ispinned(bp)) { pinned++; continue; } Here >>>>>> if (!xfs_buf_trylock(bp)) continue; This means submission is stuck until something else triggers a log force to unpin the buffer. To get onto the delwri list to begin with, the buffer pin state has already been checked, and hence it's relatively rare we get a race between flushing and encountering a pinned buffer in delwri submission to begin with. Further, to increase the pin count the buffer has to be locked, so the only way we can hit this race without failing the trylock is to be preempted between the pincount check seeing zero and the trylock being run. Hence to avoid this problem, just invert the order of trylock vs pin check. We shouldn't hit that many pinned buffers here, so optimising away the trylock for pinned buffers should not matter for performance at all. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Chandan Babu R <chandan.babu@oracle.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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.