+ mm-fix-filemap_get_folios_contig-returning-batches-of-identical-folios.patch added to mm-hotfixes-unstable branch

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

The patch titled
     Subject: mm: fix filemap_get_folios_contig returning batches of identical folios
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-fix-filemap_get_folios_contig-returning-batches-of-identical-folios.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-filemap_get_folios_contig-returning-batches-of-identical-folios.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Vishal Moola (Oracle)" <vishal.moola@gmail.com>
Subject: mm: fix filemap_get_folios_contig returning batches of identical folios
Date: Thu, 3 Apr 2025 16:54:17 -0700

filemap_get_folios_contig() is supposed to return distinct folios found
within [start, end].  Large folios in the Xarray become multi-index
entries.  xas_next() can iterate through the sub-indexes before finding a
sibling entry and breaking out of the loop.

This can result in a returned folio_batch containing an indeterminate
number of duplicate folios, which forces the callers to skeptically handle
the returned batch.  This is inefficient and incurs a large maintenance
overhead.

We can fix this by calling xas_advance() after we have successfully adding
a folio to the batch to ensure our Xarray is positioned such that it will
correctly find the next folio - similar to filemap_get_read_batch().

Link: https://lkml.kernel.org/r/Z-8s1-kiIDkzgRbc@fedora
Fixes: 35b471467f88 ("filemap: add filemap_get_folios_contig()")
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reported-by: Qu Wenruo <quwenruo.btrfs@gmx.com>
Closes: https://lkml.kernel.org/r/b714e4de-2583-4035-b829-72cfb5eb6fc6@gmx.com
Tested-by: Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Vivek Kasireddy <vivek.kasireddy@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/filemap.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/filemap.c~mm-fix-filemap_get_folios_contig-returning-batches-of-identical-folios
+++ a/mm/filemap.c
@@ -2244,6 +2244,7 @@ unsigned filemap_get_folios_contig(struc
 			*start = folio->index + nr;
 			goto out;
 		}
+		xas_advance(&xas, folio_next_index(folio) - 1);
 		continue;
 put_folio:
 		folio_put(folio);
_

Patches currently in -mm which might be from vishal.moola@gmail.com are

mm-compaction-fix-bug-in-hugetlb-handling-pathway.patch
mm-fix-filemap_get_folios_contig-returning-batches-of-identical-folios.patch
mm-compaction-use-folio-in-hugetlb-pathway.patch