nvme: change namespaces_mutext to namespaces_rwsem
namespaces_mutext is used to synchronize the operations on ctrl namespaces list. Most of the time, it is a read operation. On the other hand, there are many interfaces in nvme core that need this lock, such as nvme_wait_freeze, and even more interfaces will be added. If we use mutex here, circular dependency could be introduced easily. For example: context A context B nvme_xxx nvme_xxx hold namespaces_mutext require namespaces_mutext sync context B So it is better to change it from mutex to rwsem. Reviewed-by: NKeith Busch <keith.busch@intel.com> Signed-off-by: NJianchao Wang <jianchao.w.wang@oracle.com> Signed-off-by: NSagi Grimberg <sagi@grimberg.me> Signed-off-by: NJens Axboe <axboe@kernel.dk>
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