From: Eric Sandeen <sandeen@redhat.com>
Date: Tue, 12 May 2009 17:39:34 -0400
Subject: [block] blktrace: only tear down our own debug/block
Message-id: <4A09B456.1000805@redhat.com>
Patchwork-id: 19994
O-Subject: [PATCH RHEL5.4] blktrace: don't tear down debug/block unless we
	created it
Bugzilla: 498489
RH-Acked-by: Jeff Moyer <jmoyer@redhat.com>

For Bug 498489 - blktrace stops working after a trace-file-directory replacement

Not sure if this'll make the 5.4 beta cut or not but putting
it out there.  It's a pretty simple fix to be sure that blktrace
isn't cleaning up things it didn't create, which stops blktrace
from working properly from that point ...

Backport of upstream patch:

From: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Date: Wed, 21 Nov 2007 11:25:41 +0000 (+0100)
Subject: blktrace: Make sure BLKTRACETEARDOWN does the full cleanup.
X-Git-Tag: v2.6.24-rc4~87^2~5
X-Git-Url: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=35fc51e7a5056889421270c1fb63d8ec45fbccf4

blktrace: Make sure BLKTRACETEARDOWN does the full cleanup.

if blktrace program segfault it will not be able
to call BLKTRACETEARDOWN. Now if we run the blktrace
again that would result in a failure to create the
block/<device> debugfs directory.This will result
in blk_remove_root() to be called which will set
blk_tree_root to NULL. But the  debugfs block dir
still exist because it contain subdirectory.

Now if we try to fix it using BLKTRACETEARDOWN
it won't work because blk_tree_root is NULL.

Fix the same.

Tested as below

root@qemu-image:/home/kvaneesh/blktrace# ./blktrace  -d /dev/hdc
Segmentation fault
root@qemu-image:/home/kvaneesh/blktrace# ./blktrace  -d /dev/hdc
BLKTRACESETUP: No such file or directory
Failed to start trace on /dev/hdc
root@qemu-image:/home/kvaneesh/blktrace# ./blktrace  -k /dev/hdc
root@qemu-image:/home/kvaneesh/blktrace# ./blktrace  -d /dev/hdc

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/block/blktrace.c b/block/blktrace.c
index f7dc5c6..4493aa2 100644
--- a/block/blktrace.c
+++ b/block/blktrace.c
@@ -179,6 +179,7 @@ static void blk_remove_tree(struct dentry *dir)
 static struct dentry *blk_create_tree(const char *blk_name)
 {
 	struct dentry *dir = NULL;
+	int created = 0;
 
 	mutex_lock(&blk_tree_mutex);
 
@@ -186,13 +187,17 @@ static struct dentry *blk_create_tree(const char *blk_name)
 		blk_tree_root = debugfs_create_dir("block", NULL);
 		if (!blk_tree_root)
 			goto err;
+		created = 1;
 	}
 
 	dir = debugfs_create_dir(blk_name, blk_tree_root);
 	if (dir)
 		root_users++;
-	else
-		blk_remove_root();
+	else {
+		/* Delete root only if we created it */
+		if (created)
+			blk_remove_root();
+	}
 
 err:
 	mutex_unlock(&blk_tree_mutex);