Patch "ext4: remove array of buffer_heads from mext_page_mkuptodate()" has been added to the 6.11-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ext4: remove array of buffer_heads from mext_page_mkuptodate()

to the 6.11-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ext4-remove-array-of-buffer_heads-from-mext_page_mku.patch
and it can be found in the queue-6.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8921f8944eea6b10790df7a6d255b7f804b83561
Author: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Date:   Thu Jul 18 23:30:01 2024 +0100

    ext4: remove array of buffer_heads from mext_page_mkuptodate()
    
    [ Upstream commit a40759fb16ae839f8c769174fde017564ea564ff ]
    
    Iterate the folio's list of buffer_heads twice instead of keeping
    an array of pointers.  This solves a too-large-array-for-stack problem
    on architectures with a ridiculoously large PAGE_SIZE and prepares
    ext4 to support larger folios.
    
    Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
    Link: https://patch.msgid.link/20240718223005.568869-3-willy@xxxxxxxxxxxxx
    Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
    Stable-dep-of: 2f3d93e210b9 ("ext4: fix race in buffer_head read fault injection")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 7a80c32fd7326..42b52b6491a03 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -165,15 +165,14 @@ mext_folio_double_lock(struct inode *inode1, struct inode *inode2,
 	return 0;
 }
 
-/* Force page buffers uptodate w/o dropping page's lock */
-static int
-mext_page_mkuptodate(struct folio *folio, unsigned from, unsigned to)
+/* Force folio buffers uptodate w/o dropping folio's lock */
+static int mext_page_mkuptodate(struct folio *folio, size_t from, size_t to)
 {
 	struct inode *inode = folio->mapping->host;
 	sector_t block;
-	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
+	struct buffer_head *bh, *head;
 	unsigned int blocksize, block_start, block_end;
-	int i, nr = 0;
+	int nr = 0;
 	bool partial = false;
 
 	BUG_ON(!folio_test_locked(folio));
@@ -214,20 +213,23 @@ mext_page_mkuptodate(struct folio *folio, unsigned from, unsigned to)
 			continue;
 		}
 		ext4_read_bh_nowait(bh, 0, NULL);
-		BUG_ON(nr >= MAX_BUF_PER_PAGE);
-		arr[nr++] = bh;
+		nr++;
 	}
 	/* No io required */
 	if (!nr)
 		goto out;
 
-	for (i = 0; i < nr; i++) {
-		bh = arr[i];
+	bh = head;
+	do {
+		if (bh_offset(bh) + blocksize <= from)
+			continue;
+		if (bh_offset(bh) > to)
+			break;
 		wait_on_buffer(bh);
 		if (buffer_uptodate(bh))
 			continue;
 		return -EIO;
-	}
+	} while ((bh = bh->b_this_page) != head);
 out:
 	if (!partial)
 		folio_mark_uptodate(folio);