linux/ipc
J. Bruce Fields b21996e36c locks: break delegations on unlink
We need to break delegations on any operation that changes the set of
links pointing to an inode.  Start with unlink.

Such operations also hold the i_mutex on a parent directory.  Breaking a
delegation may require waiting for a timeout (by default 90 seconds) in
the case of a unresponsive NFS client.  To avoid blocking all directory
operations, we therefore drop locks before waiting for the delegation.
The logic then looks like:

	acquire locks
	...
	test for delegation; if found:
		take reference on inode
		release locks
		wait for delegation break
		drop reference on inode
		retry

It is possible this could never terminate.  (Even if we take precautions
to prevent another delegation being acquired on the same inode, we could
get a different inode on each retry.)  But this seems very unlikely.

The initial test for a delegation happens after the lock on the target
inode is acquired, but the directory inode may have been acquired
further up the call stack.  We therefore add a "struct inode **"
argument to any intervening functions, which we use to pass the inode
back up to the caller in the case it needs a delegation synchronously
broken.

Cc: David Howells <dhowells@redhat.com>
Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: Dustin Kirkland <dustin.kirkland@gazzang.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2013-11-09 00:16:42 -05:00
..
compat_mq.c ipc: initialize structure memory to zero for compat functions 2010-10-27 18:03:13 -07:00
compat.c get rid of union semop in sys_semctl(2) arguments 2013-03-05 15:14:16 -05:00
ipc_sysctl.c ipc: add sysctl to specify desired next object id 2013-01-04 16:11:45 -08:00
ipcns_notifier.c ipc: do not use a negative value to re-enable msgmni automatic recomputing 2008-07-25 10:53:42 -07:00
Makefile Add generic sys_ipc wrapper 2010-03-12 15:52:32 -08:00
mq_sysctl.c mqueue: separate mqueue default value from maximum value 2012-05-31 17:49:31 -07:00
mqueue.c locks: break delegations on unlink 2013-11-09 00:16:42 -05:00
msg.c ipc,msg: prevent race with rmid in msgsnd,msgrcv 2013-09-30 14:31:03 -07:00
msgutil.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-05-01 17:51:54 -07:00
namespace.c ipc: drop ipc_lock_by_ptr 2013-09-11 15:59:44 -07:00
sem.c ipc/sem.c: update sem_otime for all operations 2013-09-30 14:31:03 -07:00
shm.c ipc: fix race with LSMs 2013-09-24 09:36:53 -07:00
syscall.c get rid of union semop in sys_semctl(2) arguments 2013-03-05 15:14:16 -05:00
util.c ipc: fix race with LSMs 2013-09-24 09:36:53 -07:00
util.h ipc: fix race with LSMs 2013-09-24 09:36:53 -07:00