block, bfq: honor already-setup queue merges
stable inclusion from linux-4.19.207 commit 2c1b1848357dc69f62ce3630b850e6680b87854b -------------------------------- [ Upstream commit 2d52c58b ] The function bfq_setup_merge prepares the merging between two bfq_queues, say bfqq and new_bfqq. To this goal, it assigns bfqq->new_bfqq = new_bfqq. Then, each time some I/O for bfqq arrives, the process that generated that I/O is disassociated from bfqq and associated with new_bfqq (merging is actually a redirection). In this respect, bfq_setup_merge increases new_bfqq->ref in advance, adding the number of processes that are expected to be associated with new_bfqq. Unfortunately, the stable-merging mechanism interferes with this setup. After bfqq->new_bfqq has been set by bfq_setup_merge, and before all the expected processes have been associated with bfqq->new_bfqq, bfqq may happen to be stably merged with a different queue than the current bfqq->new_bfqq. In this case, bfqq->new_bfqq gets changed. So, some of the processes that have been already accounted for in the ref counter of the previous new_bfqq will not be associated with that queue. This creates an unbalance, because those references will never be decremented. This commit fixes this issue by reestablishing the previous, natural behaviour: once bfqq->new_bfqq has been set, it will not be changed until all expected redirections have occurred. Signed-off-by: NDavide Zini <davidezini2@gmail.com> Signed-off-by: NPaolo Valente <paolo.valente@linaro.org> Link: https://lore.kernel.org/r/20210802141352.74353-2-paolo.valente@linaro.orgSigned-off-by: NJens Axboe <axboe@kernel.dk> Signed-off-by: NSasha Levin <sashal@kernel.org> Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Showing
想要评论请 注册 或 登录