Nest rename_lock inside vfsmount_lock
commit 7ea600b5314529f9d1b9d6d3c41cb26fce6a7a4a upstream.
... lest we get livelocks between path_is_under() and d_path() and friends.
The thing is, wrt fairness lglocks are more similar to rwsems than to rwlocks;
it is possible to have thread B spin on attempt to take lock shared while thread
A is already holding it shared, if B is on lower-numbered CPU than A and there's
a thread C spinning on attempt to take the same lock exclusive.
As the result, we need consistent ordering between vfsmount_lock (lglock) and
rename_lock (seq_lock), even though everything that takes both is going to take
vfsmount_lock only shared.
Spotted-by: Brad Spengler <spender@grsecurity.net>
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[ zhj: backport to 3.4:
- Adjust context
- s/&vfsmount_lock/vfsmount_lock/]
Signed-off-by: Zhao Hongjiang <zhaohongjiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Change-Id: I731cf1ca80e6d1a4cbff8902aad6c38ac58bfb32
1 file changed