Re: [2.6.21] circular locking dependency found in QUOTA OFF

[Jan Kara <jack@suse.cz>]

  Hi,

  Thanks for report. It seems like a lockdep problem. i_mutex for quota
files is below dqonoff_sem. We were already fixing this for filesystem
specific quota IO functions but obviously we've missed a few cases. I
wonder why it showed up only now... Anyway, attached is a fix. Andrew,
would you add it? Thanks.

								Honza

On Mon 14-05-07 19:43:18, Michal Piotrowski wrote:
> [adding Jan and fsdevel to CC]
> 
> Hi Folkert,
> 
> On 14/05/07, Folkert van Heusden <folkert@vanheusden.com> wrote:
> >Hi,
> >
> >When I cleanly reboot my pc running 2.6.21 on a P4 with HT and 2GB of ram
> >and system on an 1-filesystem IDE disk, I get the following circular
> >locking dependency error:
> >
> >[330961.226405] =======================================================
> >[330961.226489] [ INFO: possible circular locking dependency detected ]
> >[330961.226531] 2.6.21 #5
> >[330961.226569] -------------------------------------------------------
> >[330961.226611] quotaoff/12249 is trying to acquire lock:
> >[330961.226652]  (&sb->s_type->i_mutex_key#4){--..}, at: [<c120e2a1>]
> >mutex_lock+0x8/0xa
> >[330961.226861]
> >[330961.226862] but task is already holding lock:
> >[330961.226938]  (&s->s_dquot.dqonoff_mutex){--..}, at: [<c120e2a1>]
> >mutex_lock+0x8/0xa
> >[330961.227111]
> >[330961.227111] which lock already depends on the new lock.
> >[330961.227112]
> >[330961.227225]
> >[330961.227225] the existing dependency chain (in reverse order) is:
> >[330961.227303]
> >[330961.227303] -> #1 (&s->s_dquot.dqonoff_mutex){--..}:
> >[330961.227473]        [<c1039b02>] check_prev_add+0x15b/0x281
> >[330961.227766]        [<c1039cb3>] check_prevs_add+0x8b/0xe8
> >[330961.228056]        [<c103b683>] __lock_acquire+0x692/0xb81
> >[330961.228353]        [<c103bfda>] lock_acquire+0x62/0x81
> >[330961.228643]        [<c120e322>] __mutex_lock_slowpath+0x75/0x28c
> >[330961.228934]        [<c120e2a1>] mutex_lock+0x8/0xa
> >[330961.229221]        [<c109fbbe>] vfs_quota_on_inode+0xc1/0x25f
> >[330961.229513]        [<c109fdd1>] vfs_quota_on+0x75/0x79
> >[330961.229803]        [<c10bc92d>] ext3_quota_on+0x95/0xb0
> >[330961.230093]        [<c10a1eb2>] do_quotactl+0xc9/0x2dd
> >[330961.230384]        [<c10a214a>] sys_quotactl+0x84/0xd6
> >[330961.230673]        [<c1003f74>] syscall_call+0x7/0xb
> >[330961.230963]        [<ffffffff>] 0xffffffff
> >[330961.231268]
> >[330961.231268] -> #0 (&sb->s_type->i_mutex_key#4){--..}:
> >[330961.231469]        [<c10399db>] check_prev_add+0x34/0x281
> >[330961.231759]        [<c1039cb3>] check_prevs_add+0x8b/0xe8
> >[330961.232049]        [<c103b683>] __lock_acquire+0x692/0xb81
> >[330961.232344]        [<c103bfda>] lock_acquire+0x62/0x81
> >[330961.232632]        [<c120e322>] __mutex_lock_slowpath+0x75/0x28c
> >[330961.232923]        [<c120e2a1>] mutex_lock+0x8/0xa
> >[330961.233211]        [<c109fa6c>] vfs_quota_off+0x1cf/0x260
> >[330961.233500]        [<c10a2088>] do_quotactl+0x29f/0x2dd
> >[330961.233792]        [<c10a214a>] sys_quotactl+0x84/0xd6
> >[330961.234081]        [<c1003f74>] syscall_call+0x7/0xb
> >[330961.234503]        [<ffffffff>] 0xffffffff
> >[330961.234795]
> >[330961.234795] other info that might help us debug this:
> >[330961.234796]
> >[330961.234908] 2 locks held by quotaoff/12249:
> >[330961.234947]  #0:  (&type->s_umount_key#15){----}, at: [<c1070b5d>]
> >get_super+0x53/0x94
> >[330961.235183]  #1:  (&s->s_dquot.dqonoff_mutex){--..}, at: [<c120e2a1>]
> >mutex_lock+0x8/0xa
> >[330961.235386]
> >[330961.235387] stack backtrace:
> >[330961.235462]  [<c1004d53>] show_trace_log_lvl+0x1a/0x30
> >[330961.235535]  [<c1004d7b>] show_trace+0x12/0x14
> >[330961.235606]  [<c1004e75>] dump_stack+0x16/0x18
> >[330961.235679]  [<c1039352>] print_circular_bug_tail+0x6f/0x71
> >[330961.235753]  [<c10399db>] check_prev_add+0x34/0x281
> >[330961.235825]  [<c1039cb3>] check_prevs_add+0x8b/0xe8
> >[330961.235897]  [<c103b683>] __lock_acquire+0x692/0xb81
> >[330961.235969]  [<c103bfda>] lock_acquire+0x62/0x81
> >[330961.236041]  [<c120e322>] __mutex_lock_slowpath+0x75/0x28c
> >[330961.236113]  [<c120e2a1>] mutex_lock+0x8/0xa
> >[330961.236185]  [<c109fa6c>] vfs_quota_off+0x1cf/0x260
> >[330961.236257]  [<c10a2088>] do_quotactl+0x29f/0x2dd
> >[330961.236330]  [<c10a214a>] sys_quotactl+0x84/0xd6
> >[330961.236402]  [<c1003f74>] syscall_call+0x7/0xb
> >[330961.236473]  =======================
> >
> 
> Is this a 2.6.21 regression?
> 
> Regards,
> Michal
> 
> -- 
> Michal K. K. Piotrowski
> Kernel Monkeys
> (http://kernel.wikidot.com/start)
-- 
Jan Kara <jack@suse.cz>
SuSE CR Labs

i_mutex on quota files is special. Unlike i_mutexes for other inodes it is
acquired under dqonoff_mutex. Tell lockdep about this lock ranking. Also
comment and code in quota_sync_sb() seem to be bogus (as i_mutex for quota
file can be acquired under dqonoff_mutex). Move truncate_inode_pages()
call under dqonoff_mutex and save some problems with races...

Signed-off-by: Jan Kara <jack@suse.cz>

diff -rupX /home/jack/.kerndiffexclude linux-2.6.21/fs/dquot.c linux-2.6.21-1-quota_lockdep/fs/dquot.c
--- linux-2.6.21/fs/dquot.c	2007-05-15 14:18:47.000000000 +0200
+++ linux-2.6.21-1-quota_lockdep/fs/dquot.c	2007-05-15 14:22:47.000000000 +0200
@@ -1421,7 +1421,7 @@ int vfs_quota_off(struct super_block *sb
 			/* If quota was reenabled in the meantime, we have
 			 * nothing to do */
 			if (!sb_has_quota_enabled(sb, cnt)) {
-				mutex_lock(&toputinode[cnt]->i_mutex);
+				mutex_lock_nested(&toputinode[cnt]->i_mutex, I_MUTEX_QUOTA);
 				toputinode[cnt]->i_flags &= ~(S_IMMUTABLE |
 				  S_NOATIME | S_NOQUOTA);
 				truncate_inode_pages(&toputinode[cnt]->i_data, 0);
diff -rupX /home/jack/.kerndiffexclude linux-2.6.21/fs/quota.c linux-2.6.21-1-quota_lockdep/fs/quota.c
--- linux-2.6.21/fs/quota.c	2006-11-29 22:57:37.000000000 +0100
+++ linux-2.6.21-1-quota_lockdep/fs/quota.c	2007-05-15 15:15:44.000000000 +0200
@@ -158,7 +158,6 @@ static int check_quotactl_valid(struct s
 static void quota_sync_sb(struct super_block *sb, int type)
 {
 	int cnt;
-	struct inode *discard[MAXQUOTAS];
 
 	sb->s_qcop->quota_sync(sb, type);
 	/* This is not very clever (and fast) but currently I don't know about
@@ -168,29 +167,21 @@ static void quota_sync_sb(struct super_b
 		sb->s_op->sync_fs(sb, 1);
 	sync_blockdev(sb->s_bdev);
 
-	/* Now when everything is written we can discard the pagecache so
-	 * that userspace sees the changes. We need i_mutex and so we could
-	 * not do it inside dqonoff_mutex. Moreover we need to be carefull
-	 * about races with quotaoff() (that is the reason why we have own
-	 * reference to inode). */
+	/*
+	 * Now when everything is written we can discard the pagecache so
+	 * that userspace sees the changes.
+	 */
 	mutex_lock(&sb_dqopt(sb)->dqonoff_mutex);
 	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
-		discard[cnt] = NULL;
 		if (type != -1 && cnt != type)
 			continue;
 		if (!sb_has_quota_enabled(sb, cnt))
 			continue;
-		discard[cnt] = igrab(sb_dqopt(sb)->files[cnt]);
+		mutex_lock_nested(&sb_dqopt(sb)->files[cnt]->i_mutex, I_MUTEX_NESTED);
+		truncate_inode_pages(&sb_dqopt(sb)->files[cnt]->i_data, 0);
+		mutex_unlock(&sb_dqopt(sb)->files[cnt]->i_mutex);
 	}
 	mutex_unlock(&sb_dqopt(sb)->dqonoff_mutex);
-	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
-		if (discard[cnt]) {
-			mutex_lock(&discard[cnt]->i_mutex);
-			truncate_inode_pages(&discard[cnt]->i_data, 0);
-			mutex_unlock(&discard[cnt]->i_mutex);
-			iput(discard[cnt]);
-		}
-	}
 }
 
 void sync_dquots(struct super_block *sb, int type)