Re: [PATCH] filemap: Handle error return from __filemap_get_folio()

[Andrew Morton <akpm@linux-foundation.org>]

On Sat, 6 May 2023 10:34:31 -0700 Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Sat, May 6, 2023 at 10:10 AM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > .. in the meantime, I did end up applying your patch.
> 
> Final (?) note on this: I not only applied your patch, but went
> looking for any other missed cases.
> 
> And found one in fs/nfs/dir.c, which like ext4 had grown a new use of
> __filemap_get_folio().
> 
> But unlike ext4 it hadn't been caught in linux-next (or I had just
> missed it) and so I hadn't caught it in my merge either.
> 
> I hope that's the last one.
> 
> I grepped for all these __filemap_get_folio() cases when I did the MM
> merge that brought in that change (and did the ext4 merge fixup), but
> then the nfs pull happened later and I didn't think to check for new
> cases...
> 
> A current grep seems to say that it's all good. But we had all missed
> the second check in filemap_fault(), so...
> 

We have a related afs fix which I plan to send over later today:

From: Christoph Hellwig <hch@lst.de>
Subject: afs: fix the afs_dir_get_folio return value
Date: Wed, 3 May 2023 17:45:26 +0200

Keep returning NULL on failure instead of letting an ERR_PTR escape to
callers that don't expect it.

Link: https://lkml.kernel.org/r/20230503154526.1223095-2-hch@lst.de
Fixes: 66dabbb65d67 ("mm: return an ERR_PTR from __filemap_get_folio")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: David Howells <dhowells@redhat.com>
Tested-by: David Howells <dhowells@redhat.com>
Cc: Marc Dionne <marc.dionne@auristor.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/afs/dir_edit.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/fs/afs/dir_edit.c~afs-fix-the-afs_dir_get_folio-return-value
+++ a/fs/afs/dir_edit.c
@@ -115,11 +115,12 @@ static struct folio *afs_dir_get_folio(s
 	folio = __filemap_get_folio(mapping, index,
 				    FGP_LOCK | FGP_ACCESSED | FGP_CREAT,
 				    mapping->gfp_mask);
-	if (IS_ERR(folio))
+	if (IS_ERR(folio)) {
 		clear_bit(AFS_VNODE_DIR_VALID, &vnode->flags);
-	else if (folio && !folio_test_private(folio))
+		return NULL;
+	}
+	if (!folio_test_private(folio))
 		folio_attach_private(folio, (void *)1);
-
 	return folio;
 }
 
_