NFSD: WARN when freeing an item still linked via nf_lru

Add a guardrail to prevent freeing memory that is still on a list.
This includes either a dispose list or the LRU list.

This is the sign of a bug, but this class of bugs can be detected
so that they don't endanger system stability, especially while
debugging.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 777698a..f58685f 100644 (file)
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -214,6 +214,14 @@ nfsd_file_free(struct nfsd_file *nf)
                fput(nf->nf_file);
                flush = true;
        }
+
+       /*
+        * If this item is still linked via nf_lru, that's a bug.
+        * WARN and leak it to preserve system stability.
+        */
+       if (WARN_ON_ONCE(!list_empty(&nf->nf_lru)))
+               return flush;
+
        call_rcu(&nf->nf_rcu, nfsd_file_slab_free);
        return flush;
 }
@@ -343,7 +351,7 @@ nfsd_file_dispose_list(struct list_head *dispose)
 
        while(!list_empty(dispose)) {
                nf = list_first_entry(dispose, struct nfsd_file, nf_lru);
-               list_del(&nf->nf_lru);
+               list_del_init(&nf->nf_lru);
                nfsd_file_flush(nf);
                nfsd_file_put_noref(nf);
        }
@@ -357,7 +365,7 @@ nfsd_file_dispose_list_sync(struct list_head *dispose)
 
        while(!list_empty(dispose)) {
                nf = list_first_entry(dispose, struct nfsd_file, nf_lru);
-               list_del(&nf->nf_lru);
+               list_del_init(&nf->nf_lru);
                nfsd_file_flush(nf);
                if (!refcount_dec_and_test(&nf->nf_ref))
                        continue;