On Mon, Jan 13, 2025 at 05:49:43AM -0800, Christoph Hellwig wrote: > On Mon, Jan 13, 2025 at 05:24:46PM +0800, Ming Lei wrote: > > > Please state the locks. Nothing fs internal here, that report is > > > about i_rwsem. And a false positive because it is about ordering > > > of i_rwsem on the upper file system sitting on the loop device vs the > > > one on the lower file systems sitting below the block device. These > > > obviously can't deadlock, we just need to tell lockdep about that fact. > > > > How can you guarantee that some code won't submit IO by grabbing the > > i_rwsem? > > ? A lot of the I/O will grab i_rwsem on the underlying device. > Basically all writes, and for many file systems also on reads. But > that is an entirely different i_rwsem as the one held the bio submitter > as that is in different file system. There is no way the top file > system can lock i_rwsem on the lower file system except through the > loop driver, and that always sits below the freeze protection. > > > As I explained, it is fine to move out vfs_fsync() out of freeze queue. > > > > Actually any lock which depends on freeze queue needs to take a careful > > look, because freeze queue connects too many global/sub-system locks. > > For block layer locks: absolutely. For file systems lock: not at all, > because we're talking about different file systems instances. The only > exception would be file systems taking global locks in the I/O path, > but I sincerely hope no one does that. Didn't you see the report on fs_reclaim and sysfs root lock? https://lore.kernel.org/linux-block/197b07435a736825ab40dab8d91db031c7fce37e.camel@xxxxxxxxxxxxxxx/ Thanks, Ming
