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Ross Lagerwall
7bbda96776
[ Upstream commit7090426351] We have seen rare IO stalls as follows: * blk_mq_plug_issue_direct() is entered with an mq_list containing two requests. * For the first request, it sets last == false and enters the driver's queue_rq callback. * The driver queue_rq callback indirectly calls schedule() which calls blk_flush_plug(). This may happen if the driver has the BLK_MQ_F_BLOCKING flag set and is allowed to sleep in ->queue_rq. * blk_flush_plug() handles the remaining request in the mq_list. mq_list is now empty. * The original call to queue_rq resumes (with last == false). * The loop in blk_mq_plug_issue_direct() terminates because there are no remaining requests in mq_list. The IO is now stalled because the last request submitted to the driver had last == false and there was no subsequent call to commit_rqs(). Fix this by returning early in blk_mq_flush_plug_list() if rq_count is 0 which it will be in the recursive case, rather than checking if the mq_list is empty. At the same time, adjust one of the callers to skip the mq_list empty check as it is not necessary. Fixes:dc5fc361d8("block: attempt direct issue of plug list") Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com> Reviewed-by: Bart Van Assche <bvanassche@acm.org> Link: https://lore.kernel.org/r/20230714101106.3635611-1-ross.lagerwall@citrix.com Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Sasha Levin <sashal@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.