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When we resize a struct sbitmap_queue, we update the wakeup batch size, but we don't update the wait count in the struct sbq_wait_states. If we resized down from a size which could use a bigger batch size, these counts could be too large and cause us to miss necessary wakeups. To fix this, update the wait counts when we resize (ensuring some careful memory ordering so that it's safe w.r.t. concurrent clears). This also fixes a theoretical issue where two threads could end up bumping the wait count up by the batch size, which could also potentially lead to hangs. Reported-by: Martin Raiber <martin@urbackup.org> Fixes:e3a2b3f931("blk-mq: allow changing of queue depth through sysfs") Fixes:2971c35f35("blk-mq: bitmap tag: fix race on blk_mq_bitmap_tags::wake_cnt") Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.