On Mon, Nov 30, 2020 at 03:31:42PM -0800, Boris Burkov wrote: > On Mon, Nov 23, 2020 at 05:50:40PM +0100, David Sterba wrote: > > On Wed, Nov 18, 2020 at 03:06:16PM -0800, Boris Burkov wrote: > > > Mounting rw and remounting from ro to rw naturally share invariants and > > > functionality which result in a correctly setup rw filesystem. Luckily, > > > there is even a strong unity in the code which implements them. In > > > mount's open_ctree, these operations mostly happen after an early return > > > for ro file systems, and in remount, they happen in a section devoted to > > > remounting ro->rw, after some remount specific validation passes. > > > > > > However, there are unfortunately a few differences. There are small > > > deviations in the order of some of the operations, remount does not > > > cleanup orphan inodes in root_tree or fs_tree, remount does not create > > > the free space tree, and remount does not handle "one-shot" mount > > > options like clear_cache and uuid tree rescan. > > > > > > Since we want to add building the free space tree to remount, and since > > > it is possible to leak orphans on a filesystem mounted as ro then > > > remounted rw > > > > The statement is not specific if the orphans are files or roots. But I > > don't agree that a leak is possible, or need a proof of the claim above. > > > > The mount-time orphan cleanup will start early, but otherwise orphan > > cleanup is checked and started on dentry lookups (btrfs_lookup_dentry). > > Deleted but not clened tree roorts are all found and removed, regardless > > of rw or ro->rw mount. > > > > So I wonder if you claim there's a leak just by lack of an explicit call > > on the remount path. > > For what it's worth, the example I had in mind is the free space inode > orphans after a block_group delete or the new "clear v1 space cache" > code in this stack. > > I hadn't considered btrfs_lookup_dentry because I was focused on those > specific inodes, but it's possible that gets called in a way that would > clean them too. > > However, another thing I think I overlooked is that it doesn't look > like remount would affect the set of delayed_iputs, so that mechanism for > removing the orphans should still work. Further, the new function only > runs when going from ro->rw, but any ro mount would run delayed iputs > before completing as part of btrfs_commit_super. > > So with all that, I agree with you that there isn't a leak. Going > forward with this, I can certainly fix the commit messages, or even get > rid of the patch that does the orphan cleanup in remount. I can't think > of a reason that the cleanup would be bad, but on the other hand, just > "unity" is a flimsy justification for adding it. Let me know what you > prefer.
Thanks for checking, the committed changelog does not contain 'leak' and I slighthly rephrased only that sentence.
