reiserfs: Fix unwanted recursive reiserfs lock in reiserfs_unlink()

reiserfs_unlink() may or may not be called under the reiserfs
lock.
But it also takes the reiserfs lock and can then acquire it
recursively which leads to do_journal_begin_r() that fails to
relax the reiserfs lock before grabbing the journal mutex,
creating an unexpected lock inversion.

We need to ensure reiserfs_unlink() won't get the reiserfs lock
recursively using reiserfs_write_lock_once().

This fixes the following warning that precedes a lock inversion
report (reiserfs lock <-> journal mutex).

------------[ cut here ]------------
WARNING: at fs/reiserfs/lock.c:95 reiserfs_lock_check_recursive+0x3a/0x50()
Hardware name: MS-7418
Unwanted recursive reiserfs lock!
Pid: 3208, comm: dbench Not tainted 2.6.32-atom #177
Call Trace:
[<c114327a>] ? reiserfs_lock_check_recursive+0x3a/0x50
[<c114327a>] ? reiserfs_lock_check_recursive+0x3a/0x50
[<c10373a7>] warn_slowpath_common+0x67/0xc0
[<c114327a>] ? reiserfs_lock_check_recursive+0x3a/0x50
[<c1037446>] warn_slowpath_fmt+0x26/0x30
[<c114327a>] reiserfs_lock_check_recursive+0x3a/0x50
[<c113c213>] do_journal_begin_r+0x83/0x360
[<c105eb16>] ? __lock_acquire+0x1296/0x19e0
[<c1142a57>] ? xattr_unlink+0x57/0xb0
[<c113c670>] journal_begin+0x80/0x130
[<c1116d5d>] reiserfs_unlink+0x7d/0x2d0
[<c1142a57>] ? xattr_unlink+0x57/0xb0
[<c1142a57>] ? xattr_unlink+0x57/0xb0
[<c1142a57>] ? xattr_unlink+0x57/0xb0
[<c1142a64>] xattr_unlink+0x64/0xb0
[<c1143169>] delete_one_xattr+0x29/0x100
[<c11427ab>] reiserfs_for_each_xattr+0x10b/0x290
[<c1143140>] ? delete_one_xattr+0x0/0x100
[<c1401ca9>] ? mutex_lock_nested+0x299/0x340
[<c11429aa>] reiserfs_delete_xattrs+0x1a/0x60
[<c11432f9>] ? reiserfs_write_lock_once+0x29/0x50
[<c111ea1f>] reiserfs_delete_inode+0x9f/0x150
[<c11b0d0f>] ? _atomic_dec_and_lock+0x4f/0x70
[<c111e980>] ? 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
[<c10505c6>] ? up_read+0x16/0x30
[<c1022ab7>] ? do_page_fault+0x187/0x330
[<c1002fd8>] ? restore_all_notrace+0x0/0x18
[<c1022930>] ? do_page_fault+0x0/0x330
[<c105cbe4>] ? trace_hardirqs_on_caller+0x124/0x170
[<c10c0a00>] sys_unlink+0x10/0x20
[<c1002ec4>] sysenter_do_call+0x12/0x32
---[ end trace 2e35d71a6cc69d0c ]---

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/namei.c

···
 	struct reiserfs_transaction_handle th;
 	int jbegin_count;
 	unsigned long savelink;
+	int depth;
 
 	inode = dentry->d_inode;
 
···
 	    JOURNAL_PER_BALANCE_CNT * 2 + 2 +
 	    4 * REISERFS_QUOTA_TRANS_BLOCKS(dir->i_sb);
 
-	reiserfs_write_lock(dir->i_sb);
+	depth = reiserfs_write_lock_once(dir->i_sb);
 	retval = journal_begin(&th, dir->i_sb, jbegin_count);
 	if (retval)
 		goto out_unlink;
···
 
 	retval = journal_end(&th, dir->i_sb, jbegin_count);
 	reiserfs_check_path(&path);
-	reiserfs_write_unlock(dir->i_sb);
+	reiserfs_write_unlock_once(dir->i_sb, depth);
 	return retval;
 
       end_unlink:
···
 	if (err)
 		retval = err;
       out_unlink:
-	reiserfs_write_unlock(dir->i_sb);
+	reiserfs_write_unlock_once(dir->i_sb, depth);
 	return retval;
 }