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 DdxvnzIB Hpks7ySQR0cYHc91eQPZS91lrUAgzVJMdqdYxM0bDCSreVI1fJw0J5jMT2SwPnt+nF9ktBWsUBhMFcBvwfx09GCOnIkhRlJNq0tuJ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: * Chuck Lever [240215 12:40]: > On Thu, Feb 15, 2024 at 12:00:08PM -0500, Liam R. Howlett wrote: > > * Jan Kara [240215 08:16]: > > > On Tue 13-02-24 16:38:08, Chuck Lever wrote: > > > > From: Chuck Lever > > > > > > > > Liam says that, unlike with xarray, once the RCU read lock is > > > > released ma_state is not safe to re-use for the next mas_find() call. > > > > But the RCU read lock has to be released on each loop iteration so > > > > that dput() can be called safely. > > > > > > > > Thus we are forced to walk the offset tree with fresh state for each > > > > directory entry. mt_find() can do this for us, though it might be a > > > > little less efficient than maintaining ma_state locally. > > > > > > > > Since offset_iterate_dir() doesn't build ma_state locally any more, > > > > there's no longer a strong need for offset_find_next(). Clean up by > > > > rolling these two helpers together. > > > > > > > > Signed-off-by: Chuck Lever > > > > > > Well, in general I think even xas_next_entry() is not safe to use how > > > offset_find_next() was using it. Once you drop rcu_read_lock(), > > > xas->xa_node could go stale. But since you're holding inode->i_rwsem when > > > using offset_find_next() you should be protected from concurrent > > > modifications of the mapping (whatever the underlying data structure is) - > > > that's what makes xas_next_entry() safe AFAIU. Isn't that enough for the > > > maple tree? Am I missing something? > > > > If you are stopping, you should be pausing the iteration. Although this > > works today, it's not how it should be used because if we make changes > > (ie: compaction requires movement of data), then you may end up with a > > UAF issue. We'd have no way of knowing you are depending on the tree > > structure to remain consistent. > > > > IOW the inode->i_rwsem is protecting writes of data but not the > > structure holding the data. > > > > This is true for both xarray and maple tree. > > Would it be appropriate to reorder this series so 7/7 comes before > the transition to use Maple Tree? I think it would, yes. Thanks, Liam