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.
