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>

diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
index c752ae9fad6cf4c840598453ae8ced674f16ea5c..b1c44ec1a3f36dabe6d03ca4b8b6d75141d5c35d 100644 (file)
--- a/drivers/infiniband/core/umem_odp.c
+++ b/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))