Patch "NFSD: WARN when freeing an item still linked via nf_lru" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    NFSD: WARN when freeing an item still linked via nf_lru

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nfsd-warn-when-freeing-an-item-still-linked-via-nf_l.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 0010a4c12645edcaeaf7272d2ee2f2673cf88db3
Author: Chuck Lever <chuck.lever@xxxxxxxxxx>
Date:   Fri Jul 8 14:25:04 2022 -0400

    NFSD: WARN when freeing an item still linked via nf_lru
    
    [ Upstream commit 668ed92e651d3c25f9b6e8cb7ceca54d00daa96d ]
    
    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@xxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 60c51a4d8e0d7..d9b5f1e183976 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -213,6 +213,14 @@ 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;
 }
@@ -342,7 +350,7 @@ 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);
 	}
@@ -356,7 +364,7 @@ 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;