[ 3.8.y.z extended stable ] Patch "Btrfs: hold the tree mod lock in __tree_mod_log_rewind" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    Btrfs: hold the tree mod lock in __tree_mod_log_rewind

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From ce56da49819941a7a25588a41dea10fe856aeb89 Mon Sep 17 00:00:00 2001
From: Josef Bacik <jbacik at fusionio.com>
Date: Sat, 29 Jun 2013 23:15:19 -0400
Subject: Btrfs: hold the tree mod lock in __tree_mod_log_rewind

commit f1ca7e98a67da618d8595866e0860308525154da upstream.

We need to hold the tree mod log lock in __tree_mod_log_rewind since we walk
forward in the tree mod entries, otherwise we'll end up with random entries and
trip the BUG_ON() at the front of __tree_mod_log_rewind.  This fixes the panics
people were seeing when running

find /whatever -type f -exec btrfs fi defrag {} \;

Thansk,

Signed-off-by: Josef Bacik <jbacik at fusionio.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/btrfs/ctree.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index f28b330..7a11fb7 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1122,8 +1122,8 @@ __tree_mod_log_oldest_root(struct btrfs_fs_info *fs_info,
  * time_seq).
  */
 static void
-__tree_mod_log_rewind(struct extent_buffer *eb, u64 time_seq,
-		      struct tree_mod_elem *first_tm)
+__tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct extent_buffer *eb,
+		      u64 time_seq, struct tree_mod_elem *first_tm)
 {
 	u32 n;
 	struct rb_node *next;
@@ -1133,6 +1133,7 @@ __tree_mod_log_rewind(struct extent_buffer *eb, u64 time_seq,
 	unsigned long p_size = sizeof(struct btrfs_key_ptr);

 	n = btrfs_header_nritems(eb);
+	tree_mod_log_read_lock(fs_info);
 	while (tm && tm->seq >= time_seq) {
 		/*
 		 * all the operations are recorded with the operator used for
@@ -1186,6 +1187,7 @@ __tree_mod_log_rewind(struct extent_buffer *eb, u64 time_seq,
 		if (tm->index != first_tm->index)
 			break;
 	}
+	tree_mod_log_read_unlock(fs_info);
 	btrfs_set_header_nritems(eb, n);
 }

@@ -1234,7 +1236,7 @@ tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct extent_buffer *eb,

 	extent_buffer_get(eb_rewin);
 	btrfs_tree_read_lock(eb_rewin);
-	__tree_mod_log_rewind(eb_rewin, time_seq, tm);
+	__tree_mod_log_rewind(fs_info, eb_rewin, time_seq, tm);
 	WARN_ON(btrfs_header_nritems(eb_rewin) >
 		BTRFS_NODEPTRS_PER_BLOCK(fs_info->fs_root));

@@ -1308,7 +1310,7 @@ get_old_root(struct btrfs_root *root, u64 time_seq)
 		btrfs_set_header_generation(eb, old_generation);
 	}
 	if (tm)
-		__tree_mod_log_rewind(eb, time_seq, tm);
+		__tree_mod_log_rewind(root->fs_info, eb, time_seq, tm);
 	else
 		WARN_ON(btrfs_header_level(eb) != 0);
 	WARN_ON(btrfs_header_nritems(eb) > BTRFS_NODEPTRS_PER_BLOCK(root));
--
1.8.1.2