On Mon, May 28, 2012 at 07:20:55PM +0900, Tejun Heo wrote: > Hello, Asias. > > On Mon, May 28, 2012 at 10:15:18AM +0800, Asias He wrote: > > >I don't think the patch description is correct. The lock switcihng is > > >inherently broken and the patch doesn't really fix the problem > > >although it *might* make the problem less likely. Trying to switch > > >locks while there are other accessors of the lock is simply broken, it > > >can never work without outer synchronization. > > > > Since the lock switching is broken, is it a good idea to force all > > the drivers to use the block layer provided lock? i.e. Change the > > API from > > blk_init_queue(rfn, driver_lock) to blk_init_queue(rfn). Any reason > > not to use the block layer provided one. > > I think hch tried to do that a while ago. Dunno what happened to the > patches. IIRC, the whole external lock thing was about sharing a > single lock across different request_queues. Not sure whether it's > actually beneficial enough or just a crazy broken optimization. Looks like almost all drivers get it wrong. And it's likely something like a floppy driver doesn't need an optimization: drivers/block/floppy.c: disks[dr]->queue = blk_init_queue(do_fd_request, &floppy_lock); The obvious use of this API is wrong. So how about introducing a correct one, deprecating the broken one so we can start slowly converting users? Then if someone sees a real reason for the internal lock, he will complain. > > >Your patch might make > > >the problem somewhat less likely simply because queue draining makes a > > >lot of request_queue users go away. > > > > Who will use the request_queue after blk_cleanup_queue()? > > Anyone who still holds a ref might try to issue a new request on a > dead queue. ie. blkdev with filesystem mounted goes away and the FS > issues a new read request after blk_cleanup_queue() finishes drainig. > > Thanks. > > -- > tejun > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
