On Sun, 2010-07-18 at 02:47 -0400, Christoph Hellwig wrote: > On Fri, Jul 16, 2010 at 03:45:00PM +0300, Artem Bityutskiy wrote: > > From: Artem Bityutskiy <Artem.Bityutskiy@xxxxxxxxx> > > > > Current bdi code has the following race between 'bdi_wb_shutdown()' > > and 'bdi_forker_thread()'. > > > > Initial condition: BDI_pending is cleaned, bdi has no writeback thread, > > because it was inactive and exited, 'bdi_wb_shutdown()' and > > 'bdi_forker_thread()' are executed concurrently. > > Wouldn't it be better to have a per-bdi mutex to serialize thread > creation and shutdown? There are several parties which want to have some serialization with bdi trheads creation and shutdown: 1. 'bdi_queue_work()' - this should not take any mutex and should be fast. It uses spinlock and this is should stay this way 2. I'm going to modify '__mark_inode_dirty()' to wake-up bdi thread - this is similar to 'bdi_queue_work()' 3. 'bdi_wb_shutdown()' - this uses the 'BDI_pending' for serialization now, but can use a mutex instead. I guess you mean that for 1 and 2 things stay the same, but for 3 we can use a mutex. Then the forker thread should also take this mutex. Right? If yes, this looks fine for me. I am going to try this approach. Then --> > And please also kill the bit wait in favour > of a proper wait queue - the bit wait interface really is just a hack > for structures that are very size sensitive, which the backing device > is not. --> the bit should go away and so no wait queue will be needed as well. -- Best Regards, Artem Bityutskiy (Артём Битюцкий) -- 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
