linux-ext4 - [patch] fix up lock order reversal in writeback

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: <20101116110058.GA4298@amd>
Date:	Tue, 16 Nov 2010 22:00:58 +1100
From:	Nick Piggin <npiggin@...nel.dk>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-btrfs@...r.kernel.org
Subject: [patch] fix up lock order reversal in writeback

I saw a lock order warning on ext4 trigger. This should solve it.
Raciness shouldn't matter much, because writeback can stop just
after we make the test and return anyway (so the API is racy anyway).

Signed-off-by: Nick Piggin <npiggin@...nel.dk>

Index: linux-2.6/fs/fs-writeback.c
===================================================================
--- linux-2.6.orig/fs/fs-writeback.c	2010-11-16 21:44:32.000000000 +1100
+++ linux-2.6/fs/fs-writeback.c	2010-11-16 21:49:37.000000000 +1100
@@ -1125,16 +1125,20 @@ EXPORT_SYMBOL(writeback_inodes_sb);
  *
  * Invoke writeback_inodes_sb if no writeback is currently underway.
  * Returns 1 if writeback was started, 0 if not.
+ *
+ * May be called inside i_lock. May not start writeback if locks cannot
+ * be acquired.
  */
 int writeback_inodes_sb_if_idle(struct super_block *sb)
 {
 	if (!writeback_in_progress(sb->s_bdi)) {
-		down_read(&sb->s_umount);
-		writeback_inodes_sb(sb);
-		up_read(&sb->s_umount);
-		return 1;
-	} else
-		return 0;
+		if (down_read_trylock(&sb->s_umount)) {
+			writeback_inodes_sb(sb);
+			up_read(&sb->s_umount);
+			return 1;
+		}
+	}
+	return 0;
 }
 EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
 
@@ -1145,17 +1149,21 @@ EXPORT_SYMBOL(writeback_inodes_sb_if_idl
  *
  * Invoke writeback_inodes_sb if no writeback is currently underway.
  * Returns 1 if writeback was started, 0 if not.
+ *
+ * May be called inside i_lock. May not start writeback if locks cannot
+ * be acquired.
  */
 int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
 				   unsigned long nr)
 {
 	if (!writeback_in_progress(sb->s_bdi)) {
-		down_read(&sb->s_umount);
-		writeback_inodes_sb_nr(sb, nr);
-		up_read(&sb->s_umount);
-		return 1;
-	} else
-		return 0;
+		if (down_read_trylock(&sb->s_umount)) {
+			writeback_inodes_sb_nr(sb, nr);
+			up_read(&sb->s_umount);
+			return 1;
+		}
+	}
+	return 0;
 }
 EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);
 
--
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