Re: [PATCH RFC v8 1/2] fs/lock: add new callback, lm_expire_lock, to lock_manager_operations

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 




> 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







[Index of Archives]     [Linux Filesystem Development]     [Linux USB Development]     [Linux Media Development]     [Video for Linux]     [Linux NILFS]     [Linux Audio Users]     [Yosemite Info]     [Linux SCSI]

  Powered by Linux