Commit facc4e3c authored by Jeff Layton's avatar Jeff Layton Committed by Chuck Lever
Browse files

sunrpc: split cache_detail queue into request and reader lists 



Replace the single interleaved queue (which mixed cache_request and
cache_reader entries distinguished by a ->reader flag) with two
dedicated lists: cd->requests for upcall requests and cd->readers
for open file handles.

Readers now track their position via a monotonically increasing
sequence number (next_seqno) rather than by their position in the
shared list. Each cache_request is assigned a seqno when enqueued,
and a new cache_next_request() helper finds the next request at or
after a given seqno.

This eliminates the cache_queue wrapper struct entirely, simplifies
the reader-skipping loops in cache_read/cache_poll/cache_ioctl/
cache_release, and makes the data flow easier to reason about.

Signed-off-by: default avatarJeff Layton <jlayton@kernel.org>
Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
parent 552d0e17

include/linux/sunrpc/cache.h

+3 −1
Original line number Diff line number Diff line
@@ -113,9 +113,11 @@ struct cache_detail { 
	int			entries;



	/* fields for communication over channel */

	struct list_head	queue;

	struct list_head	requests;

	struct list_head	readers;

	spinlock_t		queue_lock;

	wait_queue_head_t	queue_wait;

	u64			next_seqno;



	atomic_t		writers;		/* how many time is /channel open */

	time64_t		last_close;		/* if no writers, when did last close */

net/sunrpc/cache.c

+59 −84
Original line number Diff line number Diff line
@@ -399,9 +399,11 @@ static struct delayed_work cache_cleaner; 
void sunrpc_init_cache_detail(struct cache_detail *cd)

{

	spin_lock_init(&cd->hash_lock);

	INIT_LIST_HEAD(&cd->queue);

	INIT_LIST_HEAD(&cd->requests);

	INIT_LIST_HEAD(&cd->readers);

	spin_lock_init(&cd->queue_lock);

	init_waitqueue_head(&cd->queue_wait);

	cd->next_seqno = 0;

	spin_lock(&cache_list_lock);

	cd->nextcheck = 0;

	cd->entries = 0;
@@ -796,29 +798,20 @@ void cache_clean_deferred(void *owner) 
 * On read, you get a full request, or block.

 * On write, an update request is processed.

 * Poll works if anything to read, and always allows write.

 *

 * Implemented by linked list of requests.  Each open file has

 * a ->private that also exists in this list.  New requests are added

 * to the end and may wakeup and preceding readers.

 * New readers are added to the head.  If, on read, an item is found with

 * CACHE_UPCALLING clear, we free it from the list.

 *

 */



struct cache_queue {

	struct list_head	list;

	int			reader;	/* if 0, then request */

};

struct cache_request {

	struct cache_queue	q;

	struct list_head	list;

	struct cache_head	*item;

	char			*buf;

	int			len;

	int			readers;

	u64			seqno;

};

struct cache_reader {

	struct cache_queue	q;

	struct list_head	list;

	int			offset;	/* if non-0, we have a refcnt on next request */

	u64			next_seqno;

};



static int cache_request(struct cache_detail *detail,
@@ -833,6 +826,17 @@ static int cache_request(struct cache_detail *detail, 
	return PAGE_SIZE - len;

}



static struct cache_request *

cache_next_request(struct cache_detail *cd, u64 seqno)

{

	struct cache_request *rq;



	list_for_each_entry(rq, &cd->requests, list)

		if (rq->seqno >= seqno)

			return rq;

	return NULL;

}



static ssize_t cache_read(struct file *filp, char __user *buf, size_t count,

			  loff_t *ppos, struct cache_detail *cd)

{
@@ -849,20 +853,13 @@ static ssize_t cache_read(struct file *filp, char __user *buf, size_t count, 
 again:

	spin_lock(&cd->queue_lock);

	/* need to find next request */

	while (rp->q.list.next != &cd->queue &&

	       list_entry(rp->q.list.next, struct cache_queue, list)

	       ->reader) {

		struct list_head *next = rp->q.list.next;

		list_move(&rp->q.list, next);

	}

	if (rp->q.list.next == &cd->queue) {

	rq = cache_next_request(cd, rp->next_seqno);

	if (!rq) {

		spin_unlock(&cd->queue_lock);

		inode_unlock(inode);

		WARN_ON_ONCE(rp->offset);

		return 0;

	}

	rq = container_of(rp->q.list.next, struct cache_request, q.list);

	WARN_ON_ONCE(rq->q.reader);

	if (rp->offset == 0)

		rq->readers++;

	spin_unlock(&cd->queue_lock);
@@ -876,9 +873,7 @@ static ssize_t cache_read(struct file *filp, char __user *buf, size_t count, 


	if (rp->offset == 0 && !test_bit(CACHE_PENDING, &rq->item->flags)) {

		err = -EAGAIN;

		spin_lock(&cd->queue_lock);

		list_move(&rp->q.list, &rq->q.list);

		spin_unlock(&cd->queue_lock);

		rp->next_seqno = rq->seqno + 1;

	} else {

		if (rp->offset + count > rq->len)

			count = rq->len - rp->offset;
@@ -888,9 +883,7 @@ static ssize_t cache_read(struct file *filp, char __user *buf, size_t count, 
		rp->offset += count;

		if (rp->offset >= rq->len) {

			rp->offset = 0;

			spin_lock(&cd->queue_lock);

			list_move(&rp->q.list, &rq->q.list);

			spin_unlock(&cd->queue_lock);

			rp->next_seqno = rq->seqno + 1;

		}

		err = 0;

	}
@@ -901,7 +894,7 @@ static ssize_t cache_read(struct file *filp, char __user *buf, size_t count, 
		rq->readers--;

		if (rq->readers == 0 &&

		    !test_bit(CACHE_PENDING, &rq->item->flags)) {

			list_del(&rq->q.list);

			list_del(&rq->list);

			spin_unlock(&cd->queue_lock);

			cache_put(rq->item, cd);

			kfree(rq->buf);
@@ -976,7 +969,6 @@ static __poll_t cache_poll(struct file *filp, poll_table *wait, 
{

	__poll_t mask;

	struct cache_reader *rp = filp->private_data;

	struct cache_queue *cq;



	poll_wait(filp, &cd->queue_wait, wait);
@@ -988,12 +980,8 @@ static __poll_t cache_poll(struct file *filp, poll_table *wait, 


	spin_lock(&cd->queue_lock);



	for (cq= &rp->q; &cq->list != &cd->queue;

	     cq = list_entry(cq->list.next, struct cache_queue, list))

		if (!cq->reader) {

	if (cache_next_request(cd, rp->next_seqno))

		mask |= EPOLLIN | EPOLLRDNORM;

			break;

		}

	spin_unlock(&cd->queue_lock);

	return mask;

}
@@ -1004,7 +992,7 @@ static int cache_ioctl(struct inode *ino, struct file *filp, 
{

	int len = 0;

	struct cache_reader *rp = filp->private_data;

	struct cache_queue *cq;

	struct cache_request *rq;



	if (cmd != FIONREAD || !rp)

		return -EINVAL;
@@ -1014,14 +1002,9 @@ static int cache_ioctl(struct inode *ino, struct file *filp, 
	/* only find the length remaining in current request,

	 * or the length of the next request

	 */

	for (cq= &rp->q; &cq->list != &cd->queue;

	     cq = list_entry(cq->list.next, struct cache_queue, list))

		if (!cq->reader) {

			struct cache_request *cr =

				container_of(cq, struct cache_request, q);

			len = cr->len - rp->offset;

			break;

		}

	rq = cache_next_request(cd, rp->next_seqno);

	if (rq)

		len = rq->len - rp->offset;

	spin_unlock(&cd->queue_lock);



	return put_user(len, (int __user *)arg);
@@ -1042,10 +1025,10 @@ static int cache_open(struct inode *inode, struct file *filp, 
			return -ENOMEM;

		}

		rp->offset = 0;

		rp->q.reader = 1;

		rp->next_seqno = 0;



		spin_lock(&cd->queue_lock);

		list_add(&rp->q.list, &cd->queue);

		list_add(&rp->list, &cd->readers);

		spin_unlock(&cd->queue_lock);

	}

	if (filp->f_mode & FMODE_WRITE)
@@ -1064,26 +1047,21 @@ static int cache_release(struct inode *inode, struct file *filp, 


		spin_lock(&cd->queue_lock);

		if (rp->offset) {

			struct cache_queue *cq;

			for (cq = &rp->q; &cq->list != &cd->queue;

			     cq = list_entry(cq->list.next,

					     struct cache_queue, list))

				if (!cq->reader) {

					struct cache_request *cr =

						container_of(cq,

						struct cache_request, q);

			struct cache_request *cr;



			cr = cache_next_request(cd, rp->next_seqno);

			if (cr) {

				cr->readers--;

				if (cr->readers == 0 &&

				    !test_bit(CACHE_PENDING,

					      &cr->item->flags)) {

						list_del(&cr->q.list);

					list_del(&cr->list);

					rq = cr;

				}

					break;

			}

			rp->offset = 0;

		}

		list_del(&rp->q.list);

		list_del(&rp->list);

		spin_unlock(&cd->queue_lock);



		if (rq) {
@@ -1107,14 +1085,11 @@ static int cache_release(struct inode *inode, struct file *filp, 


static void cache_dequeue(struct cache_detail *detail, struct cache_head *ch)

{

	struct cache_queue *cq, *tmp;

	struct cache_request *cr;

	struct cache_request *cr, *tmp;

	LIST_HEAD(dequeued);



	spin_lock(&detail->queue_lock);

	list_for_each_entry_safe(cq, tmp, &detail->queue, list)

		if (!cq->reader) {

			cr = container_of(cq, struct cache_request, q);

	list_for_each_entry_safe(cr, tmp, &detail->requests, list) {

		if (cr->item != ch)

			continue;

		if (test_bit(CACHE_PENDING, &ch->flags))
@@ -1122,12 +1097,12 @@ static void cache_dequeue(struct cache_detail *detail, struct cache_head *ch) 
			break;

		if (cr->readers != 0)

			continue;

			list_move(&cr->q.list, &dequeued);

		list_move(&cr->list, &dequeued);

	}

	spin_unlock(&detail->queue_lock);

	while (!list_empty(&dequeued)) {

		cr = list_entry(dequeued.next, struct cache_request, q.list);

		list_del(&cr->q.list);

		cr = list_entry(dequeued.next, struct cache_request, list);

		list_del(&cr->list);

		cache_put(cr->item, detail);

		kfree(cr->buf);

		kfree(cr);
@@ -1245,14 +1220,14 @@ static int cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h) 
		return -EAGAIN;

	}



	crq->q.reader = 0;

	crq->buf = buf;

	crq->len = 0;

	crq->readers = 0;

	spin_lock(&detail->queue_lock);

	if (test_bit(CACHE_PENDING, &h->flags)) {

		crq->item = cache_get(h);

		list_add_tail(&crq->q.list, &detail->queue);

		crq->seqno = detail->next_seqno++;

		list_add_tail(&crq->list, &detail->requests);

		trace_cache_entry_upcall(detail, h);

	} else

		/* Lost a race, no longer PENDING, so don't enqueue */