72c215ed87
commit fe630de009d0 ("md/raid10: avoid deadlock on recovery.") allowed
normal io and sync io to exist at the same time. Task hung will occur as
below:
T1 T2 T3 T4
raid10d
handle_read_error
allow_barrier
conf->nr_pending--
-> 0
//submit sync io
raid10_sync_request
raise_barrier
->will not be blocked
...
//submit to drivers
raid10_read_request
wait_barrier
conf->nr_pending++
-> 1
//retry read fail
raid10_end_read_request
reschedule_retry
add to retry_list
conf->nr_queued++
-> 1
//sync io fail
end_sync_read
__end_sync_read
reschedule_retry
add to retry_list
conf->nr_queued++
-> 2
...
handle_read_error
get form retry_list
conf->nr_queued--
freeze_array
wait nr_pending == nr_queued+1
->1 ->2
//task hung
retry read and sync io will be added to retry_list(nr_queued->2) if they
fails. raid10d() called handle_read_error() and hung in freeze_array().
nr_queued will not decrease because raid10d is blocked, nr_pending will
not increase because conf->barrier is not released.
Fix it by moving allow_barrier() after raid10_read_request().
raise_barrier() will wait for nr_waiting to become 0. Therefore, sync io
and regular io will not be issued at the same time.
Also remove the check of nr_queued in stop_waiting_barrier. It can be 0
but don't need to be blocking. Remove the check for MD_RECOVERY_RUNNING as
the check is redundent.
Fixes: fe630de009d0 ("md/raid10: avoid deadlock on recovery.")
Signed-off-by: Li Nan <linan122@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230222041000.3341651-2-linan666@huaweicloud.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.