On Thu, Nov 20, 2014 at 08:16:06AM +0000, Tim Small wrote: > On 20/11/14 06:34, Christoph Hellwig wrote: > > Wakko, any chance you could resend a patch to remove the mutex from the > > ioctl path? > > I'm trying out some local changes which removes the ex-BKL mutex from > sr_block_ioctl() in sr.c, and instead uses a per-drive mutex which I've > added to cdrom_device_info (as per Arnd Bergmann/ James Bottomley's > discussion here https://lkml.org/lkml/2012/2/28/305 ). > > This seems to work in a quick test testing (simultaneous cdparanoia on > 8-or-so drives took ~10 minutes, whereas last time I tried that it took > more than 18 hours), but I've been short on time to do much more. > > At first inspection, it looks like it's just the cdrom-specific ioctls > in drivers/cdrom/cdrom.c which aren't safely preemptible (my conclusion > based on the fact that scsi_ioctl etc. is called elsewhere without > locking (e.g. from /dev/sg and /dev/sd devices - I haven't looked at ). Yes, they are safe. Even inside cdrom_ioctl very little locking is required, but it might not be worth a lot of effort to go for fine grained locking there. > As a result, I was wondering about moving the mutex_lock / unlock, so > that they wrap just the cdrom-specific ioctl calls instead, although I > suspect there won't be a huge performance benefit from doing so, it > would have the advantage that all the code related to the new mutex to > be moved into cdrom.c That sounds fine. It gets the performance critical SG_IO out of the critical region, and replaces the silly global lock in all the CDROM drivers with a per-device lock colocated with the data protected. Totally offtopic: Jens, is it time to drop the silly paride driver? -- 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
