[PATCH] mm: BUG if filemap_alloc_folio gives us a folio with a non-NULL ->private

From: Jeff Layton <jlayton@kernel.org>
To: ceph-devel@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org,
	"Matthew Wilcox" <willy@infradead.org>,
	"Xiubo Li" <xiubli@redhat.com>,
	"Luís Henriques" <lhenriques@suse.de>
Subject: [PATCH] mm: BUG if filemap_alloc_folio gives us a folio with a non-NULL ->private
Date: Fri, 13 May 2022 10:29:52 -0400	[thread overview]
Message-ID: <20220513142952.27853-1-jlayton@kernel.org> (raw)

We've seen some instances where we call __filemap_get_folio and get back
one with a ->private value that is non-NULL. Let's have the allocator
bug if that happens.

URL: https://tracker.ceph.com/issues/55421
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Xiubo Li <xiubli@redhat.com>
Cc: Luís Henriques <lhenriques@suse.de>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 mm/filemap.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

It might not hurt to merge this into mainline. If it pops then we know
something is very wrong.

diff --git a/mm/filemap.c b/mm/filemap.c
index 9a1eef6c5d35..74c3fb062ef7 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -990,10 +990,12 @@ struct folio *filemap_alloc_folio(gfp_t gfp, unsigned int order)
 			n = cpuset_mem_spread_node();
 			folio = __folio_alloc_node(gfp, order, n);
 		} while (!folio && read_mems_allowed_retry(cpuset_mems_cookie));
-
-		return folio;
+	} else {
+		folio = folio_alloc(gfp, order);
 	}
-	return folio_alloc(gfp, order);
+	if (folio)
+		VM_BUG_ON_FOLIO(folio->private, folio);
+	return folio;
 }
 EXPORT_SYMBOL(filemap_alloc_folio);
 #endif
-- 
2.36.1

