sbitmap: Advance the queue index before waking up a queue
authorGabriel Krisman Bertazi <krisman@suse.de>
Tue, 15 Nov 2022 22:45:51 +0000 (17:45 -0500)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Fri, 10 Mar 2023 08:34:34 +0000 (09:34 +0100)
commit12815a7d8f8231f53e075087ed7c6423f8c74d20
treee9cd8a2ec508257b2b6e11f3b9084ebbd96cdc9b
parent7ebde70510a12835a2a4168e2600b41456ffc314
sbitmap: Advance the queue index before waking up a queue

commit 976570b4ecd30d3ec6e1b0910da8e5edc591f2b6 upstream.

When a queue is awaken, the wake_index written by sbq_wake_ptr currently
keeps pointing to the same queue.  On the next wake up, it will thus
retry the same queue, which is unfair to other queues, and can lead to
starvation.  This patch, moves the index update to happen before the
queue is returned, such that it will now try a different queue first on
the next wake up, improving fairness.

Fixes: 4f8126bb2308 ("sbitmap: Use single per-bitmap counting to wake up queued tags")
Reported-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Link: https://lore.kernel.org/r/20221115224553.23594-2-krisman@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
lib/sbitmap.c