[PATCH 3/3] reiserfs: Don't lock root inode searching

[Frederic Weisbecker <fweisbec@gmail.com>]

Nothing requires that we lock the filesystem until the root inode
is provided.

Also iget5_locked() triggers a warning because we are holding the
filesystem lock while allocating the inode, which result in a lockdep
suspicion that we have a lock inversion against the reclaim path:

[ 1986.896979] =================================
[ 1986.896990] [ INFO: inconsistent lock state ]
[ 1986.896997] 3.1.1-main #8
[ 1986.897001] ---------------------------------
[ 1986.897007] inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
[ 1986.897016] kswapd0/16 [HC0[0]:SC0[0]:HE1:SE1] takes:
[ 1986.897023]  (&REISERFS_SB(s)->lock){+.+.?.}, at: [<c01f8bd4>] reiserfs_write_lock+0x20/0x2a
[ 1986.897044] {RECLAIM_FS-ON-W} state was registered at:
[ 1986.897050]   [<c014a5b9>] mark_held_locks+0xae/0xd0
[ 1986.897060]   [<c014aab3>] lockdep_trace_alloc+0x7d/0x91
[ 1986.897068]   [<c0190ee0>] kmem_cache_alloc+0x1a/0x93
[ 1986.897078]   [<c01e7728>] reiserfs_alloc_inode+0x13/0x3d
[ 1986.897088]   [<c01a5b06>] alloc_inode+0x14/0x5f
[ 1986.897097]   [<c01a5cb9>] iget5_locked+0x62/0x13a
[ 1986.897106]   [<c01e99e0>] reiserfs_fill_super+0x410/0x8b9
[ 1986.897114]   [<c01953da>] mount_bdev+0x10b/0x159
[ 1986.897123]   [<c01e764d>] get_super_block+0x10/0x12
[ 1986.897131]   [<c0195b38>] mount_fs+0x59/0x12d
[ 1986.897138]   [<c01a80d1>] vfs_kern_mount+0x45/0x7a
[ 1986.897147]   [<c01a83e3>] do_kern_mount+0x2f/0xb0
[ 1986.897155]   [<c01a987a>] do_mount+0x5c2/0x612
[ 1986.897163]   [<c01a9a72>] sys_mount+0x61/0x8f
[ 1986.897170]   [<c044060c>] sysenter_do_call+0x12/0x32
[ 1986.897181] irq event stamp: 7509691
[ 1986.897186] hardirqs last  enabled at (7509691): [<c0190f34>] kmem_cache_alloc+0x6e/0x93
[ 1986.897197] hardirqs last disabled at (7509690): [<c0190eea>] kmem_cache_alloc+0x24/0x93
[ 1986.897209] softirqs last  enabled at (7508896): [<c01294bd>] __do_softirq+0xee/0xfd
[ 1986.897222] softirqs last disabled at (7508859): [<c01030ed>] do_softirq+0x50/0x9d
[ 1986.897234]
[ 1986.897235] other info that might help us debug this:
[ 1986.897242]  Possible unsafe locking scenario:
[ 1986.897244]
[ 1986.897250]        CPU0
[ 1986.897254]        ----
[ 1986.897257]   lock(&REISERFS_SB(s)->lock);
[ 1986.897265] <Interrupt>
[ 1986.897269]     lock(&REISERFS_SB(s)->lock);
[ 1986.897276]
[ 1986.897277]  *** DEADLOCK ***
[ 1986.897278]
[ 1986.897286] no locks held by kswapd0/16.
[ 1986.897291]
[ 1986.897292] stack backtrace:
[ 1986.897299] Pid: 16, comm: kswapd0 Not tainted 3.1.1-main #8
[ 1986.897306] Call Trace:
[ 1986.897314]  [<c0439e76>] ? printk+0xf/0x11
[ 1986.897324]  [<c01482d1>] print_usage_bug+0x20e/0x21a
[ 1986.897332]  [<c01479b8>] ? print_irq_inversion_bug+0x172/0x172
[ 1986.897341]  [<c014855c>] mark_lock+0x27f/0x483
[ 1986.897349]  [<c0148d88>] __lock_acquire+0x628/0x1472
[ 1986.897358]  [<c0149fae>] lock_acquire+0x47/0x5e
[ 1986.897366]  [<c01f8bd4>] ? reiserfs_write_lock+0x20/0x2a
[ 1986.897384]  [<c01f8bd4>] ? reiserfs_write_lock+0x20/0x2a
[ 1986.897397]  [<c043b5ef>] mutex_lock_nested+0x35/0x26f
[ 1986.897409]  [<c01f8bd4>] ? reiserfs_write_lock+0x20/0x2a
[ 1986.897421]  [<c01f8bd4>] reiserfs_write_lock+0x20/0x2a
[ 1986.897433]  [<c01e2edd>] map_block_for_writepage+0xc9/0x590
[ 1986.897448]  [<c01b1706>] ? create_empty_buffers+0x33/0x8f
[ 1986.897461]  [<c0121124>] ? get_parent_ip+0xb/0x31
[ 1986.897472]  [<c043ef7f>] ? sub_preempt_count+0x81/0x8e
[ 1986.897485]  [<c043cae0>] ? _raw_spin_unlock+0x27/0x3d
[ 1986.897496]  [<c0121124>] ? get_parent_ip+0xb/0x31
[ 1986.897508]  [<c01e355d>] reiserfs_writepage+0x1b9/0x3e7
[ 1986.897521]  [<c0173b40>] ? clear_page_dirty_for_io+0xcb/0xde
[ 1986.897533]  [<c014a6e3>] ? trace_hardirqs_on_caller+0x108/0x138
[ 1986.897546]  [<c014a71e>] ? trace_hardirqs_on+0xb/0xd
[ 1986.897559]  [<c0177b38>] shrink_page_list+0x34f/0x5e2
[ 1986.897572]  [<c01780a7>] shrink_inactive_list+0x172/0x22c
[ 1986.897585]  [<c0178464>] shrink_zone+0x303/0x3b1
[ 1986.897597]  [<c043cae0>] ? _raw_spin_unlock+0x27/0x3d
[ 1986.897611]  [<c01788c9>] kswapd+0x3b7/0x5f2

The deadlock shouldn't happen since we are doing that allocation in
the mount path, the filesystem is not available for any reclaim.
Still the warning is annoying.

To solve this, acquire the lock later only where we need it, right
before calling reiserfs_read_locked_inode() that wants to lock to
walk the tree.

Reported-by: Knut Petersen <Knut_Petersen@t-online.de>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jeff Mahoney <jeffm@suse.com>
---
 fs/reiserfs/super.c |   28 +++++++++++++---------------
 1 files changed, 13 insertions(+), 15 deletions(-)

diff --git a/fs/reiserfs/super.c b/fs/reiserfs/super.c
index b5f167c..7cd9313 100644
--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -1428,9 +1428,7 @@ static int read_super_block(struct super_block *s, int offset)
 static int reread_meta_blocks(struct super_block *s)
 {
 	ll_rw_block(READ, 1, &(SB_BUFFER_WITH_SB(s)));
-	reiserfs_write_unlock(s);
 	wait_on_buffer(SB_BUFFER_WITH_SB(s));
-	reiserfs_write_lock(s);
 	if (!buffer_uptodate(SB_BUFFER_WITH_SB(s))) {
 		reiserfs_warning(s, "reiserfs-2504", "error reading the super");
 		return 1;
@@ -1738,24 +1736,14 @@ static int reiserfs_fill_super(struct super_block *s, void *data, int silent)
 				 */
 	}
 
-	/*
-	 * This path assumed to be called with the BKL in the old times.
-	 * Now we have inherited the big reiserfs lock from it and many
-	 * reiserfs helpers called in the mount path and elsewhere require
-	 * this lock to be held even if it's not always necessary. Let's be
-	 * conservative and hold it early. The window can be reduced after
-	 * careful review of the code.
-	 */
-	reiserfs_write_lock(s);
-
 	if (reread_meta_blocks(s)) {
 		SWARN(silent, s, "jmacd-9",
 		      "unable to reread meta blocks after journal init");
-		goto error;
+		goto error_unlocked;
 	}
 
 	if (replay_only(s))
-		goto error;
+		goto error_unlocked;
 
 	if (bdev_read_only(s->s_bdev) && !(s->s_flags & MS_RDONLY)) {
 		SWARN(silent, s, "clm-7000",
@@ -1769,9 +1757,19 @@ static int reiserfs_fill_super(struct super_block *s, void *data, int silent)
 			 reiserfs_init_locked_inode, (void *)(&args));
 	if (!root_inode) {
 		SWARN(silent, s, "jmacd-10", "get root inode failed");
-		goto error;
+		goto error_unlocked;
 	}
 
+	/*
+	 * This path assumed to be called with the BKL in the old times.
+	 * Now we have inherited the big reiserfs lock from it and many
+	 * reiserfs helpers called in the mount path and elsewhere require
+	 * this lock to be held even if it's not always necessary. Let's be
+	 * conservative and hold it early. The window can be reduced after
+	 * careful review of the code.
+	 */
+	reiserfs_write_lock(s);
+
 	if (root_inode->i_state & I_NEW) {
 		reiserfs_read_locked_inode(root_inode, &args);
 		unlock_new_inode(root_inode);
-- 
1.7.5.4