On Tue, 2007-01-23 at 16:53 -0800, Ed Lin wrote: > The block layer uses lock to protect request queue. Every scsi device > has a unique request queue, and queue lock is the default lock in struct > request_queue. This is good for normal cases. But for a host with > shared queue tag (e.g. stex controllers), a queue lock per device means > the shared queue tag is not protected when multiple devices are accessed > at a same time. This patch is a simple fix for this situation by introducing > a host queue lock to protect shared queue tag. Without this patch we will > see various kernel panics (including the BUG() and kernel errors in > blk_queue_start_tag and blk_queue_end_tag of ll_rw_blk.c) when accessing > different devices simultaneously (e.g. copying big file from one device to > another in smp kernels). This patch looks OK in principle. However, are you sure you're not using a sledgehammer to crack a nut? If the only reason you're doing this is because of the shared tag map, then probably that should be the area you protect with a per-tag-map lock. The net effect of what you've done will be to serialise all accesses to your storage devices. For a small number of devices, this probably won't matter than much, but for large numbers of devices, you're probably going to introduce artificial performance degredation in the I/O scheduler. James - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
