IB/core: Annotate umem_mutex acquisition under fs_reclaim for lockdep

Following the fix in the previous commit ("IB/mlx5: Fix potential
deadlock in MR deregistration"), teach lockdep explicitly about the
locking order between fs_reclaim and umem_mutex.

The previous commit resolved a potential deadlock scenario where
kzalloc(GFP_KERNEL) was called while holding umem_mutex, which could
lead to reclaim and eventually invoke the MMU notifier
(mlx5_ib_invalidate_range()), causing a recursive acquisition of
umem_mutex.

To prevent such issues from reoccurring unnoticed in future code
changes, add a lockdep annotation in ib_init_umem_odp() that simulates
taking umem_mutex inside a reclaim context. This makes lockdep aware
of this locking dependency and ensures that future violations—such as
calling kzalloc() or any memory allocator that may enter reclaim while
holding umem_mutex—will immediately raise a lockdep warning.

Signed-off-by: Or Har-Toov <[email protected]>
Reviewed-by: Michael Guralnik <[email protected]>
Link: https://patch.msgid.link/9d31b9d8fe1db648a9f47cec3df6b8463319dee5.1750061698.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <[email protected]>

Author: ohartoov

drivers/infiniband/core/umem_odp.c

@@ -76,6 +76,17 @@ static int ib_init_umem_odp(struct ib_umem_odp *umem_odp,
 	end = ALIGN(end, page_size);
 	if (unlikely(end < page_size))
 		return -EOVERFLOW;
+	/*
+	 * The mmu notifier can be called within reclaim contexts and takes the
+	 * umem_mutex. This is rare to trigger in testing, teach lockdep about
+	 * it.
+	 */
+	if (IS_ENABLED(CONFIG_LOCKDEP)) {
+		fs_reclaim_acquire(GFP_KERNEL);
+		mutex_lock(&umem_odp->umem_mutex);
+		mutex_unlock(&umem_odp->umem_mutex);
+		fs_reclaim_release(GFP_KERNEL);
+	}
 
 	nr_entries = (end - start) >> PAGE_SHIFT;
 	if (!(nr_entries * PAGE_SIZE / page_size))