Re: [PATCH v3 6/7] mm/memfd_luo: remove folio from page cache when accounting fails

[Andrew Morton]

On Thu, 02 Apr 2026 11:52:57 +0000 Pratyush Yadav <pratyush@xxxxxxxxxx> wrote:

> So I think the commit message needs reworking. Perhaps something like
> the below:
>
> ...
>
> With that,
> 
> Reviewed-by: Pratyush Yadav <pratyush@xxxxxxxxxx>

Thanks, I did this:

From: Chenghao Duan <duanchenghao@xxxxxxxxxx>
Subject: mm/memfd_luo: remove folio from page cache when accounting fails
Date: Thu, 26 Mar 2026 16:47:26 +0800

In memfd_luo_retrieve_folios(), when shmem_inode_acct_blocks() fails
after successfully adding the folio to the page cache, the code jumps
to unlock_folio without removing the folio from the page cache.

While the folio eventually will be freed when the file is released by
memfd_luo_retrieve(), it is a good idea to directly remove a folio that
was not fully added to the file.  This avoids the possibility of
accounting mismatches in shmem or filemap core.

Fix by adding a remove_from_cache label that calls
filemap_remove_folio() before unlocking, matching the error handling
pattern in shmem_alloc_and_add_folio().

This issue was identified by AI review:
https://sashiko.dev/#/patchset/20260323110747.193569-1-duanchenghao@xxxxxxxxxx

[pratyush@xxxxxxxxxx: changelog alterations]
  Link: https://lkml.kernel.org/r/2vxzzf3lfujq.fsf@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20260326084727.118437-7-duanchenghao@xxxxxxxxxx
Signed-off-by: Chenghao Duan <duanchenghao@xxxxxxxxxx>
Reviewed-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Reviewed-by: Pratyush Yadav <pratyush@xxxxxxxxxx>
Cc: Haoran Jiang <jianghaoran@xxxxxxxxxx>
Cc: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/memfd_luo.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/memfd_luo.c~mm-memfd_luo-remove-folio-from-page-cache-when-accounting-fails
+++ a/mm/memfd_luo.c
@@ -461,7 +461,7 @@ static int memfd_luo_retrieve_folios(str
 		if (err) {
 			pr_err("shmem: failed to account folio index %ld(%ld pages): %d\n",
 			       i, npages, err);
-			goto unlock_folio;
+			goto remove_from_cache;
 		}
 
 		nr_added_pages += npages;
@@ -474,6 +474,8 @@ static int memfd_luo_retrieve_folios(str
 
 	return 0;
 
+remove_from_cache:
+	filemap_remove_folio(folio);
 unlock_folio:
 	folio_unlock(folio);
 	folio_put(folio);
_