From: Zhaoyang Huang zhaoyang.huang@unisoc.com
[ Upstream commit 03e02b94171b1985dd0aa184296fe94425b855a3 ]
This patch is inspired by a code review of fs codes which aims at folio's extra refcnt that could introduce unwanted behavious when judging refcnt, such as[1].That is, the folio passed to mapping_evict_folio carries the refcnts from find_lock_entries, page_cache, corresponding to PTEs and folio's private if has. However, current code doesn't take the refcnt for folio's private which could have mapping_evict_folio miss the one to only PTE and lead to call filemap_release_folio wrongly.
[1] long mapping_evict_folio(struct address_space *mapping, struct folio *folio) { ... //current code will misjudge here if there is one pte on the folio which is be deemed as the one as folio's private if (folio_ref_count(folio) > folio_nr_pages(folio) + folio_has_private(folio) +
return 0; if (!filemap_release_folio(folio, 0)) return 0; return remove_mapping(mapping, folio); }Signed-off-by: Zhaoyang Huang zhaoyang.huang@unisoc.com Signed-off-by: Anna Schumaker anna.schumaker@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org
Sorry, this patch should be dropped since Trond has explained that there is no need to grab refcnt here as nfs_page has hold the refcount on this folio.
fs/nfs/write.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/fs/nfs/write.c b/fs/nfs/write.c index d074d0ceb4f01..80c6ded5f74c6 100644 --- a/fs/nfs/write.c +++ b/fs/nfs/write.c @@ -772,8 +772,7 @@ static void nfs_inode_add_request(struct nfs_page *req) nfs_lock_request(req); spin_lock(&mapping->i_private_lock); set_bit(PG_MAPPED, &req->wb_flags);
folio_set_private(folio);folio->private = req;
folio_attach_private(folio, req); spin_unlock(&mapping->i_private_lock); atomic_long_inc(&nfsi->nrequests); /* this a head request for a page group - mark it as having an @@-797,8 +796,7 @@ static void nfs_inode_remove_request(struct nfs_page *req)
spin_lock(&mapping->i_private_lock); if (likely(folio)) {
folio->private = NULL;folio_clear_private(folio);
folio_detach_private(folio); clear_bit(PG_MAPPED,&req->wb_head->wb_flags); } spin_unlock(&mapping->i_private_lock); -- 2.43.0