868bba54a3
If reshape is in progress and io across reshape_position is issued, such io will wait for reshape to make progress(see details in the case that make_stripe_request() return STRIPE_SCHEDULE_AND_RETRY). It has been reported several times that if system reboot while growing raid5 to raid6, array assemble will hang infinitely([1, 2]). This is because following deadlock is triggered: 1) a normal io is waiting for reshape to progress, this io can be from system-udevd or mdadm. 2) while assemble, mdadm tries to suspend the array, hence 'reconfig_mutex' is held and mddev_suspend() must wait for normal io to be done. 3) daemon thread can't start reshape because 'reconfig_mutex' can't be held. 1) and 3) is unbreakable because they're foundation design. In order to break 2), following is possible solutions that I can think of: a) Let mddev_suspend() fail is not a good option, because this will break many scenarios since mddev_suspend() doesn't fail before. b) Fail the io that is waiting for reshape to make progress from mddev_suspend(). c) Return false for the io that is waiting for reshape to make progress from raid5_make_request(), and these io will wait for suspend to be done in md_handle_request(), where 'active_io' is not grabbed. c) sounds better than b), however, b) is used because it's easy and straightforward, and it's verified that mdadm can assemble in this case. On the other hand, c) breaks the logic that mddev_suspend() will wait for submitted io to be completely handled. Fix the problem by checking reshape in mddev_suspend(), if reshape can't make progress and there are still some io waiting for reshape, fail those io. [1] https://lore.kernel.org/all/CAFig2csUV2QiomUhj_t3dPOgV300dbQ6XtM9ygKPdXJFSH__Nw@mail.gmail.com/ [2] https://lore.kernel.org/all/CAO2ABipzbw6QL5eNa44CQHjiVa-LTvS696Mh9QaTw+qsUKFUCw@mail.gmail.com/ Reported-by: Jove <jovetoo@gmail.com> Reported-by: David Gilmour <dgilmour76@gmail.com> Signed-off-by: Yu Kuai <yukuai3@huawei.com> Signed-off-by: Song Liu <song@kernel.org> Link: https://lore.kernel.org/r/20230512015610.821290-6-yukuai1@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.