On Monday November 1, akpm@xxxxxxxx wrote: > Andrew Morton <akpm@xxxxxxxx> wrote: > > > > NeilBrown <neilb@xxxxxxxxxxxxxxx> wrote: > > > > > > As the unplug timer can potentially fire at any time, and > > > and it access data that is released by the md ->stop function, > > > we need to del_timer_sync before releasing that data. > > > > raid really shouldn't know about unplug_timer. > > > > I mean, if we're actually destroying the queue then blk_cleanup_queue() > should have done the right thing here. If we're not destroying the queue > then an unplug timer expiry should be benign. > > Bit confused as to what's happening here. Not surprising. It's a bit ugly. md has the misfortune of working in a way that doesn't fit very well with some aspects of the blkdev layer. To create an md array, you open /dev/mdX, and use some ioctls to set up the array. Thus the block device must exist internally as a block device before any details about it are available. Similarly, to shut down an array, you open /dev/mdX and use an ioctl to shut it down. This it will still be open (though only once) after it has been shut down. (as I understand it) I can only safely use blk_cleanup_queue on the queue after (or during) the last close. Thus I cannot use it while shutting down an array. However I need to release the md personality as part of shutting down the array, so I have to disable the unplug function (which is handled by the personality). I could change ->unplug_fn to point to something safe, but there is still a race with the timer going off at just the wrong time. Maybe an API that allowed by to change ->make_request_fn and ->unplug_fn (and possibly others) and then call some interface, and be sure that no internal use of those functions would occur after given interface was called. This interface could then just do the del_timer_sync. NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
