> On Dec 13, 2021, at 12:24 PM, Dai Ngo <dai.ngo@xxxxxxxxxx> wrote:
>
> Add new callback, lm_expire_lock, to lock_manager_operations to allow
> the lock manager to take appropriate action to resolve the lock conflict
> if possible. The callback takes 2 arguments, file_lock of the blocker
> and a testonly flag:
>
> testonly = 1 check and return lock manager's private data if lock conflict
> can be resolved else return NULL.
> testonly = 0 resolve the conflict if possible, return true if conflict
> was resolved esle return false.
>
> 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.
>
> Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
> ---
> fs/locks.c | 40 +++++++++++++++++++++++++++++++++++++---
> include/linux/fs.h | 1 +
> 2 files changed, 38 insertions(+), 3 deletions(-)
>
> diff --git a/fs/locks.c b/fs/locks.c
> index 3d6fb4ae847b..5f3ea40ce2aa 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -952,8 +952,11 @@ void
> posix_test_lock(struct file *filp, struct file_lock *fl)
> {
> struct file_lock *cfl;
> + struct file_lock *checked_cfl = NULL;
> struct file_lock_context *ctx;
> struct inode *inode = locks_inode(filp);
> + void *res_data;
> + void *(*func)(void *priv, bool testonly);
>
> ctx = smp_load_acquire(&inode->i_flctx);
> if (!ctx || list_empty_careful(&ctx->flc_posix)) {
> @@ -962,11 +965,24 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
> }
>
> spin_lock(&ctx->flc_lock);
> +retry:
> 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 (checked_cfl != cfl && cfl->fl_lmops &&
> + cfl->fl_lmops->lm_expire_lock) {
> + res_data = cfl->fl_lmops->lm_expire_lock(cfl, true);
> + if (res_data) {
> + func = cfl->fl_lmops->lm_expire_lock;
> + spin_unlock(&ctx->flc_lock);
> + func(res_data, false);
> + spin_lock(&ctx->flc_lock);
> + checked_cfl = cfl;
> + goto retry;
> + }
> }
Dai and I discussed this offline. Depending on a pointer to represent
exactly the same struct file_lock across a dropped spinlock is racy.
Dai plans to investigate other mechanisms to perform this check
reliably.
> + locks_copy_conflock(fl, cfl);
> + goto out;
> }
> fl->fl_type = F_UNLCK;
> out:
> @@ -1136,10 +1152,13 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
> struct file_lock *new_fl2 = NULL;
> struct file_lock *left = NULL;
> struct file_lock *right = NULL;
> + struct file_lock *checked_fl = NULL;
> struct file_lock_context *ctx;
> int error;
> bool added = false;
> LIST_HEAD(dispose);
> + void *res_data;
> + void *(*func)(void *priv, bool testonly);
>
> ctx = locks_get_lock_context(inode, request->fl_type);
> if (!ctx)
> @@ -1166,9 +1185,24 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
> * blocker's list of waiters and the global blocked_hash.
> */
> if (request->fl_type != F_UNLCK) {
> +retry:
> list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
> if (!posix_locks_conflict(request, fl))
> continue;
> + if (checked_fl != fl && fl->fl_lmops &&
> + fl->fl_lmops->lm_expire_lock) {
> + res_data = fl->fl_lmops->lm_expire_lock(fl, true);
> + if (res_data) {
> + func = fl->fl_lmops->lm_expire_lock;
> + spin_unlock(&ctx->flc_lock);
> + percpu_up_read(&file_rwsem);
> + func(res_data, false);
> + percpu_down_read(&file_rwsem);
> + spin_lock(&ctx->flc_lock);
> + checked_fl = fl;
> + goto retry;
> + }
> + }
> if (conflock)
> locks_copy_conflock(conflock, fl);
> error = -EAGAIN;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e7a633353fd2..8cb910c3a394 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1071,6 +1071,7 @@ 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 *);
> + void *(*lm_expire_lock)(void *priv, bool testonly);
> };
>
> struct lock_manager {
> --
> 2.9.5
>
--
Chuck Lever
