[PATCH v3 18/20] afs: Fix lack of locking around modifications of net->cells_dyn_ino

[David Howells <dhowells@redhat.com>]

Fix the lack of locking around modifications of net->cells_dyn_ino.

Fixes: 1d0b929fc070 ("afs: Change dynroot to create contents on demand")
Closes: https://sashiko.dev/#/patchset/20260618074903.2374756-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
---
 fs/afs/cell.c     | 8 +++++++-
 fs/afs/internal.h | 1 +
 fs/afs/main.c     | 1 +
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index fbb8a43aa7cd..e95e96f8200c 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -205,8 +205,12 @@ static struct afs_cell *afs_alloc_cell(struct afs_net *net,
 	cell->dns_source = vllist->source;
 	cell->dns_status = vllist->status;
 	smp_store_release(&cell->dns_lookup_count, 1); /* vs source/status */
+	idr_preload(GFP_KERNEL);
+	spin_lock(&net->cells_dyn_ino_lock);
 	ret = idr_alloc_cyclic(&net->cells_dyn_ino, cell,
-			       2, INT_MAX / 2, GFP_KERNEL);
+			       2, INT_MAX / 2, GFP_ATOMIC);
+	spin_unlock(&net->cells_dyn_ino_lock);
+	idr_preload_end();
 	if (ret < 0)
 		goto error;
 	atomic_inc(&net->cells_outstanding);
@@ -579,7 +583,9 @@ static void afs_cell_destroy(struct rcu_head *rcu)
 	afs_put_vlserverlist(net, rcu_access_pointer(cell->vl_servers));
 	afs_unuse_cell(cell->alias_of, afs_cell_trace_unuse_alias);
 	key_put(cell->anonymous_key);
+	spin_lock(&net->cells_dyn_ino_lock);
 	idr_remove(&net->cells_dyn_ino, cell->dynroot_ino);
+	spin_unlock(&net->cells_dyn_ino_lock);
 	kfree(cell->name - 1);
 	kfree(cell);
 
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 785c646856d7..c42752608383 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -293,6 +293,7 @@ struct afs_net {
 	struct idr		cells_dyn_ino;	/* cell->dynroot_ino mapping */
 	struct afs_cell __rcu	*ws_cell;
 	atomic_t		cells_outstanding;
+	spinlock_t		cells_dyn_ino_lock;
 	struct rw_semaphore	cells_lock;
 	struct mutex		cells_alias_lock;
 
diff --git a/fs/afs/main.c b/fs/afs/main.c
index 7a883c59976f..0a4a606575d7 100644
--- a/fs/afs/main.c
+++ b/fs/afs/main.c
@@ -78,6 +78,7 @@ static int __net_init afs_net_init(struct net *net_ns)
 
 	net->cells = RB_ROOT;
 	idr_init(&net->cells_dyn_ino);
+	spin_lock_init(&net->cells_dyn_ino_lock);
 	init_rwsem(&net->cells_lock);
 	mutex_init(&net->cells_alias_lock);
 	mutex_init(&net->proc_cells_lock);