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Commit5989bfe6ac("block: restore two stage elevator switch while running nr_hw_queue update") reintroduced a lockdep warning by calling blk_mq_freeze_queue_nomemsave() before switching the I/O scheduler. The function blk_mq_elv_switch_none() calls elevator_change_done(). Running this while the queue is frozen causes a lockdep warning. Fix this by reordering the operations: first, switch the I/O scheduler to 'none', and then freeze the queue. This ensures that elevator_change_done() is not called on an already frozen queue. And this way is safe because elevator_set_none() does freeze queue before switching to none. Also we still have to rely on blk_mq_elv_switch_back() for switching back, and it has to cover unfrozen queue case. Cc: Nilay Shroff <nilay@linux.ibm.com> Cc: Yu Kuai <yukuai3@huawei.com> Fixes:5989bfe6ac("block: restore two stage elevator switch while running nr_hw_queue update") Signed-off-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Yu Kuai <yukuai3@huawei.com> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Link: https://lore.kernel.org/r/20250815131737.331692-1-ming.lei@redhat.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
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
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText 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.