On Mon, 2013-07-01 at 17:17 +0200, Bart Van Assche wrote: > On 07/01/13 16:49, James Bottomley wrote: > > On Thu, 2013-06-27 at 16:56 +0200, Bart Van Assche wrote: > >> Make concurrent invocations of scsi_device_set_state() safe. > > > > Firstly, I don't understand from this where you think the races are. > > Secondly, shouldn't this be the device lock? and thirdly, if we accept > > that locking is required, encapsulate it in the function: Having the > > callers manage locking is asking for trouble. The latter may require a > > new lock for the state to avoid entanglement. > > Today there is no guarantee that scsi_device_set_state() calls are > serialized, so two scsi_device_set_state() invocations may be in > progress concurrently. It is e.g. possible that both calls report > "device state has been changed successfully" to their callers although > only one of these two state changes will be effective due to the race.
We could say the above about a significant fraction of the functions in the kernel; it's not a reason to add fine grained locking to them all. I want to know what the actual races you're trying to fix are; what causes them and, in particular, is adding yet another fine grained lock going to mitigate them effectively or should they be mediated in a different way. James -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
