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Commit 3999e493 authored by Jeff Layton's avatar Jeff Layton Committed by Al Viro
Browse files

locks: add a new "lm_owner_key" lock operation 



Currently, the hashing that the locking code uses to add these values
to the blocked_hash is simply calculated using fl_owner field. That's
valid in most cases except for server-side lockd, which validates the
owner of a lock based on fl_owner and fl_pid.

In the case where you have a small number of NFS clients doing a lot
of locking between different processes, you could end up with all
the blocked requests sitting in a very small number of hash buckets.

Add a new lm_owner_key operation to the lock_manager_operations that
will generate an unsigned long to use as the key in the hashtable.
That function is only implemented for server-side lockd, and simply
XORs the fl_owner and fl_pid.

Signed-off-by: default avatarJeff Layton <jlayton@redhat.com>
Acked-by: default avatarJ. Bruce Fields <bfields@fieldses.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 48f74186

Documentation/filesystems/Locking

+11 −5
Original line number Diff line number Diff line
@@ -349,6 +349,7 @@ fl_release_private: maybe no 
----------------------- lock_manager_operations ---------------------------

prototypes:

	int (*lm_compare_owner)(struct file_lock *, struct file_lock *);

	unsigned long (*lm_owner_key)(struct file_lock *);

	void (*lm_notify)(struct file_lock *);  /* unblock callback */

	int (*lm_grant)(struct file_lock *, struct file_lock *, int);

	void (*lm_break)(struct file_lock *); /* break_lease callback */
@@ -358,16 +359,21 @@ locking rules: 


			inode->i_lock	file_lock_lock	may block

lm_compare_owner:	yes[1]		maybe		no

lm_owner_key		yes[1]		yes		no

lm_notify:		yes		yes		no

lm_grant:		no		no		no

lm_break:		yes		no		no

lm_change		yes		no		no



[1]:	->lm_compare_owner is generally called with *an* inode->i_lock held. It

may not be the i_lock of the inode for either file_lock being compared! This is

the case with deadlock detection, since the code has to chase down the owners

of locks that may be entirely unrelated to the one on which the lock is being

acquired. When doing a search for deadlocks, the file_lock_lock is also held.

[1]:	->lm_compare_owner and ->lm_owner_key are generally called with

*an* inode->i_lock held. It may not be the i_lock of the inode

associated with either file_lock argument! This is the case with deadlock

detection, since the code has to chase down the owners of locks that may

be entirely unrelated to the one on which the lock is being acquired.

For deadlock detection however, the file_lock_lock is also held. The

fact that these locks are held ensures that the file_locks do not

disappear out from under you while doing the comparison or generating an

owner key.



--------------------------- buffer_head -----------------------------------

prototypes:

fs/lockd/svclock.c

+12 −0
Original line number Diff line number Diff line
@@ -744,8 +744,20 @@ static int nlmsvc_same_owner(struct file_lock *fl1, struct file_lock *fl2) 
	return fl1->fl_owner == fl2->fl_owner && fl1->fl_pid == fl2->fl_pid;

}



/*

 * Since NLM uses two "keys" for tracking locks, we need to hash them down

 * to one for the blocked_hash. Here, we're just xor'ing the host address

 * with the pid in order to create a key value for picking a hash bucket.

 */

static unsigned long

nlmsvc_owner_key(struct file_lock *fl)

{

	return (unsigned long)fl->fl_owner ^ (unsigned long)fl->fl_pid;

}



const struct lock_manager_operations nlmsvc_lock_operations = {

	.lm_compare_owner = nlmsvc_same_owner,

	.lm_owner_key = nlmsvc_owner_key,

	.lm_notify = nlmsvc_notify_blocked,

	.lm_grant = nlmsvc_grant_deferred,

};

fs/locks.c

+10 −2
Original line number Diff line number Diff line
@@ -521,10 +521,18 @@ locks_delete_global_locks(struct file_lock *fl) 
	spin_unlock(&file_lock_lock);

}



static unsigned long

posix_owner_key(struct file_lock *fl)

{

	if (fl->fl_lmops && fl->fl_lmops->lm_owner_key)

		return fl->fl_lmops->lm_owner_key(fl);

	return (unsigned long)fl->fl_owner;

}



static inline void

locks_insert_global_blocked(struct file_lock *waiter)

{

	hash_add(blocked_hash, &waiter->fl_link, (unsigned long)waiter->fl_owner);

	hash_add(blocked_hash, &waiter->fl_link, posix_owner_key(waiter));

}



static inline void
@@ -757,7 +765,7 @@ static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl) 
{

	struct file_lock *fl;



	hash_for_each_possible(blocked_hash, fl, fl_link, (unsigned long)block_fl->fl_owner) {

	hash_for_each_possible(blocked_hash, fl, fl_link, posix_owner_key(block_fl)) {

		if (posix_same_owner(fl, block_fl))

			return fl->fl_next;

	}

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -908,6 +908,7 @@ struct file_lock_operations { 


struct lock_manager_operations {

	int (*lm_compare_owner)(struct file_lock *, struct file_lock *);

	unsigned long (*lm_owner_key)(struct file_lock *);

	void (*lm_notify)(struct file_lock *);	/* unblock callback */

	int (*lm_grant)(struct file_lock *, struct file_lock *, int);

	void (*lm_break)(struct file_lock *);