linux-kernel - [PATCH 4.2.y-ckt 079/273] btrfs: fix clone / extent-same deadlocks

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Message-Id: <1457391064-6660-80-git-send-email-kamal@canonical.com>
Date:	Mon,  7 Mar 2016 14:47:50 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Mark Fasheh <mfasheh@...e.de>, Chris Mason <clm@...com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 079/273] btrfs: fix clone / extent-same deadlocks

4.2.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Mark Fasheh <mfasheh@...e.de>

commit 293a8489f300536dc6d996c35a6ebb89aa03bab2 upstream.

Clone and extent same lock their source and target inodes in opposite order.
In addition to this, the range locking in clone doesn't take ordering into
account. Fix this by having clone use the same locking helpers as
btrfs-extent-same.

In addition, I do a small cleanup of the locking helpers, removing a case
(both inodes being the same) which was poorly accounted for and never
actually used by the callers.

Signed-off-by: Mark Fasheh <mfasheh@...e.de>
Reviewed-by: David Sterba <dsterba@...e.cz>
Signed-off-by: Chris Mason <clm@...com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 fs/btrfs/ioctl.c | 34 ++++++++--------------------------
 1 file changed, 8 insertions(+), 26 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index be4e53c..5d8c740 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2842,8 +2842,7 @@ static void btrfs_double_inode_lock(struct inode *inode1, struct inode *inode2)
 		swap(inode1, inode2);
 
 	mutex_lock_nested(&inode1->i_mutex, I_MUTEX_PARENT);
-	if (inode1 != inode2)
-		mutex_lock_nested(&inode2->i_mutex, I_MUTEX_CHILD);
+	mutex_lock_nested(&inode2->i_mutex, I_MUTEX_CHILD);
 }
 
 static void btrfs_double_extent_unlock(struct inode *inode1, u64 loff1,
@@ -2861,8 +2860,7 @@ static void btrfs_double_extent_lock(struct inode *inode1, u64 loff1,
 		swap(loff1, loff2);
 	}
 	lock_extent_range(inode1, loff1, len);
-	if (inode1 != inode2)
-		lock_extent_range(inode2, loff2, len);
+	lock_extent_range(inode2, loff2, len);
 }
 
 struct cmp_pages {
@@ -3836,13 +3834,7 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 		goto out_fput;
 
 	if (!same_inode) {
-		if (inode < src) {
-			mutex_lock_nested(&inode->i_mutex, I_MUTEX_PARENT);
-			mutex_lock_nested(&src->i_mutex, I_MUTEX_CHILD);
-		} else {
-			mutex_lock_nested(&src->i_mutex, I_MUTEX_PARENT);
-			mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
-		}
+		btrfs_double_inode_lock(src, inode);
 	} else {
 		mutex_lock(&src->i_mutex);
 	}
@@ -3892,8 +3884,7 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 
 		lock_extent_range(src, lock_start, lock_len);
 	} else {
-		lock_extent_range(src, off, len);
-		lock_extent_range(inode, destoff, len);
+		btrfs_double_extent_lock(src, off, inode, destoff, len);
 	}
 
 	ret = btrfs_clone(src, inode, off, olen, len, destoff, 0);
@@ -3904,9 +3895,7 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 
 		unlock_extent(&BTRFS_I(src)->io_tree, lock_start, lock_end);
 	} else {
-		unlock_extent(&BTRFS_I(src)->io_tree, off, off + len - 1);
-		unlock_extent(&BTRFS_I(inode)->io_tree, destoff,
-			      destoff + len - 1);
+		btrfs_double_extent_unlock(src, off, inode, destoff, len);
 	}
 	/*
 	 * Truncate page cache pages so that future reads will see the cloned
@@ -3915,17 +3904,10 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 	truncate_inode_pages_range(&inode->i_data, destoff,
 				   PAGE_CACHE_ALIGN(destoff + len) - 1);
 out_unlock:
-	if (!same_inode) {
-		if (inode < src) {
-			mutex_unlock(&src->i_mutex);
-			mutex_unlock(&inode->i_mutex);
-		} else {
-			mutex_unlock(&inode->i_mutex);
-			mutex_unlock(&src->i_mutex);
-		}
-	} else {
+	if (!same_inode)
+		btrfs_double_inode_unlock(src, inode);
+	else
 		mutex_unlock(&src->i_mutex);
-	}
 out_fput:
 	fdput(src_file);
 out_drop_write:
-- 
2.7.0