4ea748e1d2
Reflinking (clone/dedupe) and rename are operations that operate on two
inodes and therefore need to lock them in the same order to avoid ABBA
deadlocks. It happens that Btrfs' reflink implementation always locked
them in a different order from VFS's lock_two_nondirectories() helper,
which is used by the rename code in VFS, resulting in ABBA type deadlocks.
Btrfs' locking order:
static void btrfs_double_inode_lock(struct inode *inode1, struct inode *inode2)
{
if (inode1 < inode2)
swap(inode1, inode2);
inode_lock_nested(inode1, I_MUTEX_PARENT);
inode_lock_nested(inode2, I_MUTEX_CHILD);
}
VFS's locking order:
void lock_two_nondirectories(struct inode *inode1, struct inode *inode2)
{
if (inode1 > inode2)
swap(inode1, inode2);
if (inode1 && !S_ISDIR(inode1->i_mode))
inode_lock(inode1);
if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)
inode_lock_nested(inode2, I_MUTEX_NONDIR2);
}
Fix this by killing the btrfs helper function that does the double inode
locking and replace it with VFS's helper lock_two_nondirectories().
Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Fixes: 416161db9b63e3 ("btrfs: offline dedupe")
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.