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

[sashiko-bot@kernel.org]

> 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@vger.kernel.org # 6.1.x
> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>

Sashiko has reviewed this patch and found no issues.

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