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locks: add a new "lm_owner_key" lock operation

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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: Jeff Layton <jlayton@redhat.com>
Acked-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Jeff Layton
2013-06-21 08:58:19 -04:00
committed by Al Viro
parent 48f7418654
commit 3999e49364
4 changed files with 34 additions and 7 deletions
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16
Documentation/filesystems/Locking
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@ -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: