RDMA/mlx5: Fix cache entry update on dereg error

BugLink: https://bugs.launchpad.net/bugs/2122072

[ Upstream commit 24d693cf6c89d216a68634d44fa93e4400775d94 ]

Fix double decrement of 'in_use' counter on push_mkey_locked() failure
while deregistering an MR.
If we fail to return an mkey to the cache in cache_ent_find_and_store()
it'll update the 'in_use' counter. Its caller, revoke_mr(), also updates
it, thus having double decrement.

Wrong value of 'in_use' counter will be exposed through debugfs and can
also cause wrong resizing of the cache when users try to set cache
entry size using the 'size' debugfs.

To address this issue, the 'in_use' counter is now decremented within
mlx5_revoke_mr() also after a successful call to
cache_ent_find_and_store() and not within cache_ent_find_and_store().
Other success or failure flows remains unchanged where it was also
decremented.

Fixes: 8c1185f ("RDMA/mlx5: Change check for cacheable mkeys")
Signed-off-by: Michael Guralnik <michaelgur@nvidia.com>
Reviewed-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://patch.msgid.link/97e979dff636f232ff4c83ce709c17c727da1fdb.1741875692.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Noah Wager <noah.wager@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

Author: mikijoy

drivers/infiniband/hw/mlx5/mr.c

@@ -1968,7 +1968,6 @@ static int cache_ent_find_and_store(struct mlx5_ib_dev *dev,
 
 	if (mr->mmkey.cache_ent) {
 		spin_lock_irq(&mr->mmkey.cache_ent->mkeys_queue.lock);
-		mr->mmkey.cache_ent->in_use--;
 		goto end;
 	}
 
@@ -2036,6 +2035,7 @@ static int mlx5_revoke_mr(struct mlx5_ib_mr *mr)
 	bool is_odp = is_odp_mr(mr);
 	bool is_odp_dma_buf = is_dmabuf_mr(mr) &&
 			!to_ib_umem_dmabuf(mr->umem)->pinned;
+	bool from_cache = !!ent;
 	int ret = 0;
 
 	if (is_odp)
@@ -2048,6 +2048,8 @@ static int mlx5_revoke_mr(struct mlx5_ib_mr *mr)
 		ent = mr->mmkey.cache_ent;
 		/* upon storing to a clean temp entry - schedule its cleanup */
 		spin_lock_irq(&ent->mkeys_queue.lock);
+		if (from_cache)
+			ent->in_use--;
 		if (ent->is_tmp && !ent->tmp_cleanup_scheduled) {
 			mod_delayed_work(ent->dev->cache.wq, &ent->dwork,
 					 msecs_to_jiffies(30 * 1000));