On Tue 24-01-12 17:59:45, Dave Chinner wrote: > On Fri, Jan 20, 2012 at 09:34:42PM +0100, Jan Kara wrote: > > In xfs we first take ilock and start transaction afterwards. > > The correct order is to allocate the transaction, reserve the space > for it and then take the ilock. We cannot hold the ilock over the > transaction reservation because that can deadlock the journal. > > That is, to make space for the new transaction reservation, we may > need to take the ilock to flush the inode and allow the journal tail > to move forwards to make space for the new transaction. If we > already hold the ilock, then it can't be flushed, we can't make > space available in the journal and hence deadlock. Thanks for clarification! > Maybe you confused the ilock vs the iolock. We can hold the iolock > over the trans alloc/reserve because that lock is not required to > move the tail of the journal, so the deadlock doesn't exist. Ups! I now had a look at what xfs_rw_ilock() does. I always thought it's just a plain rw semaphore and now I see it takes several locks depending on the argument. Ugh, a bit surprising for XFS newcomer as me ;) But now things become clearer so I fix my patches with this new knowledge in mind. So just disregard my locking comments. They were likely bogus. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
