ext4: limit group search loop for non-extent files

From: Lachlan McIlroy <[email protected]>

In the case where we are allocating for a non-extent file, we must limit the groups we allocate from to those below 2^32 blocks, and ext4_mb_regular_allocator() attempts to do this initially by putting a cap on ngroups for the subsequent search loop.

However, the initial target group comes in from the allocation context (ac), and it may already be beyond the artificially limited ngroups. In this case, the limit

	if (group == ngroups)
		group = 0;

at the top of the loop is never true, and the loop will run away.

Catch this case inside the loop and reset the search to start at group 0.

[[email protected]: add commit msg & comments]

Signed-off-by Eric Sandeen <[email protected]>

---

p.s. I suppose this limit could go after the assignment from ac->ac_g_ex.fe_group, depending on your sense of style...

fs/ext4/mballoc.c +5 -2

index ee6614b..f54baee 100644
@@ -1994,7 +1994,11 @@ repeat:
 		group = ac->ac_g_ex.fe_group;
 
 		for (i = 0; i < ngroups; group++, i++) {
-			if (group == ngroups)
+			/*
+			 * Artificially restricted ngroups for non-extent
+			 * files makes group > ngroups possible on first loop.
+			 */
+			if (group >= ngroups)
 				group = 0;
 
 			/* This now checks without needing the buddy page */
 
--

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From: Lachlan McIlroy <[email protected]>

Quoted 1 line

From: Lachlan McIlroy <[email protected]>

Note: if it's from Lachlan, it needs his Signed-off-by. Lachlan, can you send an Ack saying it's OK for me to add a:

Signed-off-by Lachlan McIlroy <[email protected]>

to the commit description?

Thanks,

- Ted

Ack. Yes Ted that's fine with me to add my Signed-off-by. Thanks.