fs/lock: add 2 callbacks to lock_manager_operations to resolve conflict

Add 2 new callbacks, lm_lock_expirable and lm_expire_lock, to
lock_manager_operations to allow the lock manager to take appropriate
action to resolve the lock conflict if possible.

A new field, lm_mod_owner, is also added to lock_manager_operations.
The lm_mod_owner is used by the fs/lock code to make sure the lock
manager module such as nfsd, is not freed while lock conflict is being
resolved.

lm_lock_expirable checks and returns true to indicate that the lock
conflict can be resolved else return false. This callback must be
called with the flc_lock held so it can not block.

lm_expire_lock is called to resolve the lock conflict if the returned
value from lm_lock_expirable is true. This callback is called without
the flc_lock held since it's allowed to block. Upon returning from
this callback, the lock conflict should be resolved and the caller is
expected to restart the conflict check from the beginnning of the list.

Lock manager, such as NFSv4 courteous server, uses this callback to
resolve conflict by destroying lock owner, or the NFSv4 courtesy client
(client that has expired but allowed to maintains its states) that owns
the lock.

Reviewed-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index c26d854275a0ec399c610af4d356d0a9d9ef0e21..0997a258361a6e8026c94fcc4886e45f042383ee 100644 (file)
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -428,6 +428,8 @@ prototypes::
        void (*lm_break)(struct file_lock *); /* break_lease callback */
        int (*lm_change)(struct file_lock **, int);
        bool (*lm_breaker_owns_lease)(struct file_lock *);
+        bool (*lm_lock_expirable)(struct file_lock *);
+        void (*lm_expire_lock)(void);
 
 locking rules:
 
@@ -439,6 +441,8 @@ lm_grant:           no              no                      no
 lm_break:              yes             no                      no
 lm_change              yes             no                      no
 lm_breaker_owns_lease: yes             no                      no
+lm_lock_expirable      yes             no                      no
+lm_expire_lock         no              no                      yes
 ====================== =============   =================       =========
 
 buffer_head

diff --git a/fs/locks.c b/fs/locks.c
index c369841ef7d190c7a5e499601d515a7f2974a5c7..ca28e0e50e569f3ad761949e71bfab646b9979c5 100644 (file)
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -902,6 +902,8 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
        struct file_lock *cfl;
        struct file_lock_context *ctx;
        struct inode *inode = locks_inode(filp);
+       void *owner;
+       void (*func)(void);
 
        ctx = smp_load_acquire(&inode->i_flctx);
        if (!ctx || list_empty_careful(&ctx->flc_posix)) {
@@ -909,12 +911,23 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
                return;
        }
 
+retry:
        spin_lock(&ctx->flc_lock);
        list_for_each_entry(cfl, &ctx->flc_posix, fl_list) {
-               if (posix_locks_conflict(fl, cfl)) {
-                       locks_copy_conflock(fl, cfl);
-                       goto out;
+               if (!posix_locks_conflict(fl, cfl))
+                       continue;
+               if (cfl->fl_lmops && cfl->fl_lmops->lm_lock_expirable
+                       && (*cfl->fl_lmops->lm_lock_expirable)(cfl)) {
+                       owner = cfl->fl_lmops->lm_mod_owner;
+                       func = cfl->fl_lmops->lm_expire_lock;
+                       __module_get(owner);
+                       spin_unlock(&ctx->flc_lock);
+                       (*func)();
+                       module_put(owner);
+                       goto retry;
                }
+               locks_copy_conflock(fl, cfl);
+               goto out;
        }
        fl->fl_type = F_UNLCK;
 out:
@@ -1088,6 +1101,8 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
        int error;
        bool added = false;
        LIST_HEAD(dispose);
+       void *owner;
+       void (*func)(void);
 
        ctx = locks_get_lock_context(inode, request->fl_type);
        if (!ctx)
@@ -1106,6 +1121,7 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
                new_fl2 = locks_alloc_lock();
        }
 
+retry:
        percpu_down_read(&file_rwsem);
        spin_lock(&ctx->flc_lock);
        /*
@@ -1117,6 +1133,17 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
                list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
                        if (!posix_locks_conflict(request, fl))
                                continue;
+                       if (fl->fl_lmops && fl->fl_lmops->lm_lock_expirable
+                               && (*fl->fl_lmops->lm_lock_expirable)(fl)) {
+                               owner = fl->fl_lmops->lm_mod_owner;
+                               func = fl->fl_lmops->lm_expire_lock;
+                               __module_get(owner);
+                               spin_unlock(&ctx->flc_lock);
+                               percpu_up_read(&file_rwsem);
+                               (*func)();
+                               module_put(owner);
+                               goto retry;
+                       }
                        if (conflock)
                                locks_copy_conflock(conflock, fl);
                        error = -EAGAIN;

diff --git a/include/linux/fs.h b/include/linux/fs.h
index b8ed7f974fb43fc5cc3c41e95991d65fdf55f315..aa6c1bbdb8c439975afa31f016751af76c9953d3 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1029,6 +1029,7 @@ struct file_lock_operations {
 };
 
 struct lock_manager_operations {
+       void *lm_mod_owner;
        fl_owner_t (*lm_get_owner)(fl_owner_t);
        void (*lm_put_owner)(fl_owner_t);
        void (*lm_notify)(struct file_lock *);  /* unblock callback */
@@ -1037,6 +1038,8 @@ struct lock_manager_operations {
        int (*lm_change)(struct file_lock *, int, struct list_head *);
        void (*lm_setup)(struct file_lock *, void **);
        bool (*lm_breaker_owns_lease)(struct file_lock *);
+       bool (*lm_lock_expirable)(struct file_lock *cfl);
+       void (*lm_expire_lock)(void);
 };
 
 struct lock_manager {