Re: [PATCH 6.1] ext4: honor NULL returns from __filemap_get_folio()

[Matthew Wilcox]

On Mon, Nov 02, 2026 at 04:33:41PM +0000, Naman Jain wrote:
> The bitmap and buddy folio conversions assume that
> __filemap_get_folio() returns error pointers. In Linux 6.1, however,
> it returns NULL both when a non-creating lookup misses and when folio
> creation fails.
> 
> A cache miss therefore passes the IS_ERR() check and reaches
> folio_test_uptodate(NULL) in ext4_mb_load_buddy_gfp(). Creating-lookup
> failures can also dereference NULL in its slow paths and in
> ext4_mb_get_buddy_page_lock().
> 
> Restore NULL checks at all six lookup sites and return -ENOMEM when a
> creating lookup fails. Preserve the folio locking and migration checks
> without changing the global filemap API.
> 
> Fixes: d34e4fd4e73f ("ext4: convert bd_bitmap_page to bd_bitmap_folio")
> Fixes: 862483175d3d ("ext4: convert bd_buddy_page to bd_buddy_folio")
> Cc: stable@xxxxxxxxxxxxxxx # 6.1.x
> Signed-off-by: Naman Jain <namjain@xxxxxxxxxxxxxxxxxxx>

Elliot beat you to it:

https://lore.kernel.org/linux-ext4/20261102-ext4-ntfs3-null-folio-v1-0-4fd91ee23a4a@xxxxxxxxxxxx/

Care to drop a R-b on his series?