From: Joanne Koong <joannelkoong@gmail.com>
Date: Fri, 29 Aug 2025 23:56:27 +0000 (-0700)
Subject: fuse: remove fuse_readpages_end() null mapping check
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=02d47e213dce6e2fa197d0cff66e92f1bc55f00f;p=thirdparty%2Fkernel%2Fstable.git

fuse: remove fuse_readpages_end() null mapping check

Remove extra logic in fuse_readpages_end() that checks against null
folio mappings. This was added in commit ce534fb05292 ("fuse: allow
splice to move pages"):

"Since the remove_from_page_cache() + add_to_page_cache_locked()
are non-atomic it is possible that the page cache is repopulated in
between the two and add_to_page_cache_locked() will fail.  This
could be fixed by creating a new atomic replace_page_cache_page()
function.

fuse_readpages_end() needed to be reworked so it works even if
page->mapping is NULL for some or all pages which can happen if the
add_to_page_cache_locked() failed."

Commit ef6a3c63112e ("mm: add replace_page_cache_page() function") added
atomic page cache replacement, which means the check against null
mappings can be removed.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 0698bcb2f9923..54786f62a9d8b 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -865,22 +865,20 @@ static void fuse_readpages_end(struct fuse_mount *fm, struct fuse_args *args,
 	struct fuse_args_pages *ap = &ia->ap;
 	size_t count = ia->read.in.size;
 	size_t num_read = args->out_args[0].size;
-	struct address_space *mapping = NULL;
-
-	for (i = 0; mapping == NULL && i < ap->num_folios; i++)
-		mapping = ap->folios[i]->mapping;
+	struct address_space *mapping;
+	struct inode *inode;
 
-	if (mapping) {
-		struct inode *inode = mapping->host;
+	WARN_ON_ONCE(!ap->num_folios);
+	mapping = ap->folios[0]->mapping;
+	inode = mapping->host;
 
-		/*
-		 * Short read means EOF. If file size is larger, truncate it
-		 */
-		if (!err && num_read < count)
-			fuse_short_read(inode, ia->read.attr_ver, num_read, ap);
+	/*
+	 * Short read means EOF. If file size is larger, truncate it
+	 */
+	if (!err && num_read < count)
+		fuse_short_read(inode, ia->read.attr_ver, num_read, ap);
 
-		fuse_invalidate_atime(inode);
-	}
+	fuse_invalidate_atime(inode);
 
 	for (i = 0; i < ap->num_folios; i++) {
 		folio_end_read(ap->folios[i], !err);