linux-ext4 - ext3: Fix ext3 block reservation early ENOSPC issue

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <1219964631.6384.70.camel@mingming-laptop>
Date:	Thu, 28 Aug 2008 16:03:51 -0700
From:	Mingming Cao <cmm@...ibm.com>
To:	linux-ext4@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>, tytso <tytso@....edu>
Subject: ext3: Fix ext3  block reservation early ENOSPC issue

From: Mingming Cao <cmm@...ibm.com>

ext3: Fix ext3 nomballoc allocator for ENOSPC

We could run into ENOSPC error on ext3, even when there is free blocks
on the filesystem.

The problem is triggered in the case the goal block group has 0 free blocks
, and the rest block groups are skipped due to the check of "free_blocks 
< windowsz/2". Current code could fall back to non reservation allocation
to prevent early ENOSPC after examing all the block groups with reservation on
, but this code was  bypassed if the reservation window is turned off already,
which is true in this case.

This patch fixed two issues:
1) We don't need to turn off block reservation if the goal block group has 
0 free blocks left and continue search for the rest of block groups.

Current code the intention is to turn off the block reservation if the
 goal allocation group has a few (some) free blocks left (not enough 
for make the desired reservation window),to try to allocation in the
 goal block group, to get better locality. But if the goal blocks have 
0 free blocks,  it should leave the block reservation on, and continues
search for the next block groups,rather than turn off block reservation
completely.

2) we don't need to check the window size if the block reservation is off. 

The problem was originally found and fixed in ext4.

Signed-off-by: Mingming Cao <cmm@...ibm.com>

---
 fs/ext3/balloc.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux-2.6.27-rc3/fs/ext3/balloc.c
===================================================================
--- linux-2.6.27-rc3.orig/fs/ext3/balloc.c	2008-08-12 18:55:39.000000000 -0700
+++ linux-2.6.27-rc3/fs/ext3/balloc.c	2008-08-28 15:52:09.000000000 -0700
@@ -1547,6 +1547,7 @@
 	 * turn off reservation for this allocation
 	 */
 	if (my_rsv && (free_blocks < windowsz)
+		&& (free_blocks > 0)
 		&& (rsv_is_empty(&my_rsv->rsv_window)))
 		my_rsv = NULL;

@@ -1585,7 +1586,7 @@
 		 * free blocks is less than half of the reservation
 		 * window size.
 		 */
-		if (free_blocks <= (windowsz/2))
+		if (my_rsv && (free_blocks <= (windowsz/2)))
 			continue;

 		brelse(bitmap_bh);

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html