Patch "ext4: fix stripe-unaligned allocations" has been added to the 4.4-stable tree

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

ext4: fix stripe-unaligned allocations

to the 4.4-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-fix-stripe-unaligned-allocations.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Kara <[email protected]>
Date: Sat, 7 Oct 2017 22:37:45 +0000
Subject: ext4: fix stripe-unaligned allocations

From: Jan Kara <[email protected]>

[ Upstream commit d9b22cf9f5466a057f2a4f1e642b469fa9d73117 ]

When a filesystem is created using:

	mkfs.ext4 -b 4096 -E stride=512 <dev>

and we try to allocate 64MB extent, we will end up directly in ext4_mb_complex_scan_group(). This is because the request is detected as power-of-two allocation (so we start in ext4_mb_regular_allocator() with ac_criteria == 0) however the check before ext4_mb_simple_scan_group() refuses the direct buddy scan because the allocation request is too large. Since cr == 0, the check whether we should use ext4_mb_scan_aligned() fails as well and we fall back to ext4_mb_complex_scan_group().

Fix the problem by checking for upper limit on power-of-two requests directly when detecting them.

---
 fs/ext4/mballoc.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

@@ -2136,8 +2136,10 @@ ext4_mb_regular_allocator(struct ext4_al
 	 * We search using buddy data only if the order of the request
 	 * is greater than equal to the sbi_s_mb_order2_reqs
 	 * You can tune it via /sys/fs/ext4/<partition>/mb_order2_req
+	 * We also support searching for power-of-two requests only for
+	 * requests upto maximum buddy size we have constructed.
 	 */
-	if (i >= sbi->s_mb_order2_reqs) {
+	if (i >= sbi->s_mb_order2_reqs && i <= sb->s_blocksize_bits + 2) {
 		/*
 		 * This should tell if fe_len is exactly power of 2
 		 */

@@ -2207,7 +2209,7 @@ repeat:
 			}
 
 			ac->ac_groups_scanned++;
-			if (cr == 0 && ac->ac_2order < sb->s_blocksize_bits+2)
+			if (cr == 0)
 				ext4_mb_simple_scan_group(ac, &e4b);
 			else if (cr == 1 && sbi->s_stripe &&
 					!(ac->ac_g_ex.fe_len % sbi->s_stripe))

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/ext4-fix-stripe-unaligned-allocations.patch queue-4.4/ext4-do-not-use-stripe_width-if-it-is-not-set.patch