[PATCH v1] fs: Move might_sleep() annotation to iput_final()

[Mickaël Salaün]

iput() don't directly call any sleepable code but mostly checks flags
and decrement a reference counter before calling iput_final() and then
evict().

Some code might call iput() with guarantees that iput_final() will not
be called.  This is the case for Landlock's hook_sb_delete() where the
inode counter must de decremented while holding it with another
reference, see comment above the first iput() call.

Move the new might_sleep() call from iput() to iput_final().  The
alternative would be to manually decrement the counter without calling
iput(), but it doesn't seem right.

Cc: Christian Brauner <brauner at kernel.org>
Cc: Edward Adam Davis <eadavis at qq.com>
Cc: Günther Noack <gnoack at google.com>
Cc: Hillf Danton <hdanton at sina.com>
Cc: Jan Kara <jack at suse.cz>
Cc: Jann Horn <jannh at google.com>
Cc: Mateusz Guzik <mjguzik at gmail.com>
Cc: Max Kellermann <max.kellermann at ionos.com>
Cc: Tingmao Wang <m at maowtm.org>
Reported-by: syzbot+12479ae15958fc3f54ec at syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/68d32659.a70a0220.4f78.0012.GAE@google.com/
Fixes: 2ef435a872ab ("fs: add might_sleep() annotation to iput() and more")
Signed-off-by: Mickaël Salaün <mic at digikod.net>
---

>From hook_sb_delete():

	/*
	 * At this point, we own the ihold() reference that was
	 * originally set up by get_inode_object() and the
	 * __iget() reference that we just set in this loop
	 * walk.  Therefore the following call to iput() will
	 * not sleep nor drop the inode because there is now at
	 * least two references to it.
	 */
	iput(inode);

#syz test

---
 fs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index 84f539497857..64120cb21e8b 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1917,6 +1917,7 @@ static void iput_final(struct inode *inode)
 	const struct super_operations *op = inode->i_sb->s_op;
 	int drop;
 
+	might_sleep();
 	WARN_ON(inode_state_read(inode) & I_NEW);
 	VFS_BUG_ON_INODE(atomic_read(&inode->i_count) != 0, inode);
 
@@ -1969,7 +1970,6 @@ static void iput_final(struct inode *inode)
  */
 void iput(struct inode *inode)
 {
-	might_sleep();
 	if (unlikely(!inode))
 		return;
 
-- 
2.51.0