Hi This is a series of patches to prevent a crash when when someone is reading block device and block size is changed simultaneously. (the crash is already happening in the production environment) The first patch adds a rw-lock to struct block_device, but doesn't use the lock anywhere. The reason why I submit this as a separate patch is that on my computer adding an unused field to this structure affects performance much more than any locking changes. The second patch uses the rw-lock. The lock is locked for read when doing I/O on the block device and it is locked for write when changing block size. The third patch converts the rw-lock to a percpu rw-lock for better performance, to avoid cache line bouncing. The fourth patch is an alternate percpu rw-lock implementation using RCU by Eric Dumazet. It avoids any atomic instruction in the hot path. Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
