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@xxxxxxxxxx>
Acked-by: J. Bruce Fields <bfields@xxxxxxxxxxxx>
---
Documentation/filesystems/Locking | 16 +++++++++++-----
fs/lockd/svclock.c | 12 ++++++++++++
fs/locks.c | 12 ++++++++++--
include/linux/fs.h | 1 +
4 files changed, 34 insertions(+), 7 deletions(-)
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 413685f..dfeb01b 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -351,6 +351,7 @@ 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 */
@@ -360,16 +361,21 @@ 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:
diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index e703318..ce2cdab 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -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,
};
diff --git a/fs/locks.c b/fs/locks.c
index d93b291..55f3af7 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -505,10 +505,18 @@ locks_delete_global_locks(struct file_lock *waiter)
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
@@ -739,7 +747,7 @@ 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;
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3b340f7..232a345 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -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 *);
--
1.7.1
--
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