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commite5c0ca1365upstream. Chuck reported [1] an IO hang problem on NFS exports that reside on SATA devices and bisected to commit615939a2ae("blk-mq: defer to the normal submission path for post-flush requests"). We analysed the IO hang problem, found there are two postflush requests waiting for each other. The first postflush request completed the REQ_FSEQ_DATA sequence, so go to the REQ_FSEQ_POSTFLUSH sequence and added in the flush pending list, but failed to blk_kick_flush() because of the second postflush request which is inflight waiting in scheduler queue. The second postflush waiting in scheduler queue can't be dispatched because the first postflush hasn't released scheduler resource even though it has completed by itself. Fix it by releasing scheduler resource when the first postflush request completed, so the second postflush can be dispatched and completed, then make blk_kick_flush() succeed. While at it, remove the check for e->ops.finish_request, as all schedulers set that. Reaffirm this requirement by adding a WARN_ON_ONCE() at scheduler registration time, just like we do for insert_requests and dispatch_request. [1] https://lore.kernel.org/all/7A57C7AE-A51A-4254-888B-FE15CA21F9E9@oracle.com/ Link: https://lore.kernel.org/linux-block/20230819031206.2744005-1-chengming.zhou@linux.dev/ Reported-by: kernel test robot <oliver.sang@intel.com> Closes: https://lore.kernel.org/oe-lkp/202308172100.8ce4b853-oliver.sang@intel.com Fixes:615939a2ae("blk-mq: defer to the normal submission path for post-flush requests") Reported-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> Tested-by: Chuck Lever <chuck.lever@oracle.com> Link: https://lore.kernel.org/r/20230813152325.3017343-1-chengming.zhou@linux.dev [axboe: folded in incremental fix and added tags] Signed-off-by: Jens Axboe <axboe@kernel.dk> [bvanassche: changed RQF_USE_SCHED into RQF_ELVPRIV; restored the finish_request pointer check before calling finish_request and removed the new warning from the elevator code. This patch fixes an I/O hang when submitting a REQ_FUA request to a request queue for a zoned block device for which FUA has been disabled (QUEUE_FLAG_FUA is not set).] Signed-off-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.