reiserfs: Safely acquire i_mutex from reiserfs_for_each_xattr

Relax the reiserfs lock before taking the inode mutex from
reiserfs_for_each_xattr() to avoid the usual bad dependencies:

=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.32-atom #179
-------------------------------------------------------
rm/3242 is trying to acquire lock:
(&sb->s_type->i_mutex_key#4/3){+.+.+.}, at: [<c11428ef>] reiserfs_for_each_xattr+0x23f/0x290

but task is already holding lock:
(&REISERFS_SB(s)->lock){+.+.+.}, at: [<c1143389>] reiserfs_write_lock+0x29/0x40

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&REISERFS_SB(s)->lock){+.+.+.}:
[<c105ea7f>] __lock_acquire+0x11ff/0x19e0
[<c105f2c8>] lock_acquire+0x68/0x90
[<c1401aab>] mutex_lock_nested+0x5b/0x340
[<c1143339>] reiserfs_write_lock_once+0x29/0x50
[<c1117022>] reiserfs_lookup+0x62/0x140
[<c10bd85f>] __lookup_hash+0xef/0x110
[<c10bf21d>] lookup_one_len+0x8d/0xc0
[<c1141e3a>] open_xa_dir+0xea/0x1b0
[<c1142720>] reiserfs_for_each_xattr+0x70/0x290
[<c11429ba>] reiserfs_delete_xattrs+0x1a/0x60
[<c111ea2f>] reiserfs_delete_inode+0x9f/0x150
[<c10c9c32>] generic_delete_inode+0xa2/0x170
[<c10c9d4f>] generic_drop_inode+0x4f/0x70
[<c10c8b07>] iput+0x47/0x50
[<c10c0965>] do_unlinkat+0xd5/0x160
[<c10c0b13>] sys_unlinkat+0x23/0x40
[<c1002ec4>] sysenter_do_call+0x12/0x32

-> #0 (&sb->s_type->i_mutex_key#4/3){+.+.+.}:
[<c105f176>] __lock_acquire+0x18f6/0x19e0
[<c105f2c8>] lock_acquire+0x68/0x90
[<c1401aab>] mutex_lock_nested+0x5b/0x340
[<c11428ef>] reiserfs_for_each_xattr+0x23f/0x290
[<c11429ba>] reiserfs_delete_xattrs+0x1a/0x60
[<c111ea2f>] reiserfs_delete_inode+0x9f/0x150
[<c10c9c32>] generic_delete_inode+0xa2/0x170
[<c10c9d4f>] generic_drop_inode+0x4f/0x70
[<c10c8b07>] iput+0x47/0x50
[<c10c0965>] do_unlinkat+0xd5/0x160
[<c10c0b13>] sys_unlinkat+0x23/0x40
[<c1002ec4>] sysenter_do_call+0x12/0x32

other info that might help us debug this:

1 lock held by rm/3242:
#0: (&REISERFS_SB(s)->lock){+.+.+.}, at: [<c1143389>] reiserfs_write_lock+0x29/0x40

stack backtrace:
Pid: 3242, comm: rm Not tainted 2.6.32-atom #179
Call Trace:
[<c13ffa13>] ? printk+0x18/0x1a
[<c105d33a>] print_circular_bug+0xca/0xd0
[<c105f176>] __lock_acquire+0x18f6/0x19e0
[<c105c932>] ? mark_held_locks+0x62/0x80
[<c105cc3b>] ? trace_hardirqs_on+0xb/0x10
[<c1401098>] ? mutex_unlock+0x8/0x10
[<c105f2c8>] lock_acquire+0x68/0x90
[<c11428ef>] ? reiserfs_for_each_xattr+0x23f/0x290
[<c11428ef>] ? reiserfs_for_each_xattr+0x23f/0x290
[<c1401aab>] mutex_lock_nested+0x5b/0x340
[<c11428ef>] ? reiserfs_for_each_xattr+0x23f/0x290
[<c11428ef>] reiserfs_for_each_xattr+0x23f/0x290
[<c1143180>] ? delete_one_xattr+0x0/0x100
[<c11429ba>] reiserfs_delete_xattrs+0x1a/0x60
[<c1143339>] ? reiserfs_write_lock_once+0x29/0x50
[<c111ea2f>] reiserfs_delete_inode+0x9f/0x150
[<c11b0d4f>] ? _atomic_dec_and_lock+0x4f/0x70
[<c111e990>] ? reiserfs_delete_inode+0x0/0x150
[<c10c9c32>] generic_delete_inode+0xa2/0x170
[<c10c9d4f>] generic_drop_inode+0x4f/0x70
[<c10c8b07>] iput+0x47/0x50
[<c10c0965>] do_unlinkat+0xd5/0x160
[<c1401098>] ? mutex_unlock+0x8/0x10
[<c10c3e0d>] ? vfs_readdir+0x7d/0xb0
[<c10c3af0>] ? filldir64+0x0/0xf0
[<c1002ef3>] ? sysenter_exit+0xf/0x16
[<c105cbe4>] ? trace_hardirqs_on_caller+0x124/0x170
[<c10c0b13>] sys_unlinkat+0x23/0x40
[<c1002ec4>] sysenter_do_call+0x12/0x32

Signed-off-by: Frederic Weisbecker <[e-mail]>
Tested-by: Christian Kujau <[e-mail]>
Cc: Alexander Beregalov <[e-mail]>
Cc: Chris Mason <[e-mail]>
Cc: Ingo Molnar <[e-mail]>

fs/reiserfs/xattr.c

···
 		err = journal_begin(&th, inode->i_sb, blocks);
 		if (!err) {
 			int jerror;
-			mutex_lock_nested(&dir->d_parent->d_inode->i_mutex,
-					  I_MUTEX_XATTR);
+			reiserfs_mutex_lock_nested_safe(
+					  &dir->d_parent->d_inode->i_mutex,
+					  I_MUTEX_XATTR, inode->i_sb);
 			err = action(dir, data);
 			jerror = journal_end(&th, inode->i_sb, blocks);
 			mutex_unlock(&dir->d_parent->d_inode->i_mutex);