IB/core: Annotate umem_mutex acquisition under fs_reclaim for lockdep

JIRA: https://issues.redhat.com/browse/RHEL-110100

commit 3f5f632
Author: Or Har-Toov <ohartoov@nvidia.com>
Date:   Mon Jun 16 11:16:03 2025 +0300

    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 <ohartoov@nvidia.com>
    Reviewed-by: Michael Guralnik <michaelgur@nvidia.com>
    Link: https://patch.msgid.link/9d31b9d8fe1db648a9f47cec3df6b8463319dee5.1750061698.git.leon@kernel.org
    Signed-off-by: Leon Romanovsky <leon@kernel.org>

Signed-off-by: Kamal Heib <kheib@redhat.com>

Author: Kamalheib

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))