afs: Fix lack of locking around modifications of net->cells_dyn_ino

Fix the lack of locking around modifications of net->cells_dyn_ino by
taking net->cells_lock exclusively.  This also requires to cell to be
removed from net->cells_dyn_ino in afs_destroy_cell_work() rather than in
afs_cell_destroy() as the latter runs in RCU cleanup context and sleeping
locks cannot be taken there.

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>
Link: https://patch.msgid.link/20260622090856.2746629-19-dhowells@redhat.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index fbb8a43aa7cd9a3b9b93244de3e2bd334c720512..9d8937ae24e219bf65820eb75f0ab8f77bd7dfa6 100644 (file)
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -205,8 +205,10 @@ 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 */
+       down_write(&net->cells_lock);
        ret = idr_alloc_cyclic(&net->cells_dyn_ino, cell,
                               2, INT_MAX / 2, GFP_KERNEL);
+       up_write(&net->cells_lock);
        if (ret < 0)
                goto error;
        atomic_inc(&net->cells_outstanding);
@@ -579,7 +581,6 @@ 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);
-       idr_remove(&net->cells_dyn_ino, cell->dynroot_ino);
        kfree(cell->name - 1);
        kfree(cell);
 
@@ -594,6 +595,11 @@ static void afs_destroy_cell_work(struct work_struct *work)
        afs_see_cell(cell, afs_cell_trace_destroy);
        timer_delete_sync(&cell->management_timer);
        cancel_work_sync(&cell->manager);
+
+       down_write(&cell->net->cells_lock);
+       idr_remove(&cell->net->cells_dyn_ino, cell->dynroot_ino);
+       up_write(&cell->net->cells_lock);
+
        call_rcu(&cell->rcu, afs_cell_destroy);
 }
 

diff --git a/fs/afs/dynroot.c b/fs/afs/dynroot.c
index 1d5e33bc750224d063446ea952d5ef97a2481010..6e3c8c691ba97f13bdf0034036e824a1617c8298 100644 (file)
--- a/fs/afs/dynroot.c
+++ b/fs/afs/dynroot.c
@@ -278,7 +278,7 @@ static struct dentry *afs_lookup_atcell(struct inode *dir, struct dentry *dentry
 }
 
 /*
- * Transcribe the cell database into readdir content under the RCU read lock.
+ * Transcribe the cell database into readdir content under net->cells_lock.
  * Each cell produces two entries, one prefixed with a dot and one not.
  */
 static int afs_dynroot_readdir_cells(struct afs_net *net, struct dir_context *ctx)