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The depth-first splitting is introduced in commit18a25da843("dm: ensure bio submission follows a depth-first tree walk"), which is used to fix the potential deadlock in case of the misordering handling of bios caused by bio_list. There're two paths submitting split bios, dm_wq_work() from worker thread and submit_bio() from application. Back upon that time, dm_wq_work() thread calls __split_and_process_bio() directly and thus will not trigger this issue since bio_list doesn't exist here. So this issue will only be triggered from application calling submit_bio(), and the fix has to check if current->bio_list is non-NULL to distinguish this case. However since commit0c2915b8c6("dm: fix missing imposition of queue_limits from dm_wq_work() thread"), dm_wq_work() thread calls submit_bio_noacct() and thus also uses bio_list. Since then all entries into __split_and_process_bio() are under protection of bio_list, and thus the checking of current->bio_list when determinning if the depth-first principle should be used, seems kind of nonsense. After all the checking always succeeds now. Fixes:0c2915b8c6("dm: fix missing imposition of queue_limits from dm_wq_work() thread") Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Signed-off-by: Mike Snitzer <snitzer@redhat.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.