bpf: Disable migration when destroying inode storage

When destroying inode storage, it invokes bpf_local_storage_destroy() to
remove all storage elements saved in the inode storage. The destroy
procedure will call bpf_selem_free() to free the element, and
bpf_selem_free() calls bpf_obj_free_fields() to free the special fields
in map value (e.g., kptr). Since kptrs may be allocated from bpf memory
allocator, migrate_{disable|enable} pairs are necessary for the freeing
of these kptrs.

To simplify reasoning about when migrate_disable() is needed for the
freeing of these dynamically-allocated kptrs, let the caller to
guarantee migration is disabled before invoking bpf_obj_free_fields().
Therefore, the patch adds migrate_{disable|enable} pair in
bpf_inode_storage_free(). The migrate_{disable|enable} pairs in the
underlying implementation of bpf_obj_free_fields() will be removed by
the following patch.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20250108010728.207536-7-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/bpf_inode_storage.c b/kernel/bpf/bpf_inode_storage.c
index a51c82dee1bd8fea98a3b39b3c6126f56ad56deb..15a3eb9b02d94c1bdd9bb6ca1600a86ab85efc79 100644 (file)
--- a/kernel/bpf/bpf_inode_storage.c
+++ b/kernel/bpf/bpf_inode_storage.c
@@ -62,16 +62,17 @@ void bpf_inode_storage_free(struct inode *inode)
        if (!bsb)
                return;
 
+       migrate_disable();
        rcu_read_lock();
 
        local_storage = rcu_dereference(bsb->storage);
-       if (!local_storage) {
-               rcu_read_unlock();
-               return;
-       }
+       if (!local_storage)
+               goto out;
 
        bpf_local_storage_destroy(local_storage);
+out:
        rcu_read_unlock();
+       migrate_enable();
 }
 
 static void *bpf_fd_inode_storage_lookup_elem(struct bpf_map *map, void *key)