[Devel] [PATCH 2/2] fs/fuse kio: simplify processing and sending kio requests

Pavel Butsykin pbutsykin at virtuozzo.com
Mon May 27 18:09:29 MSK 2019



On 27.05.2019 18:02, Kirill Tkhai wrote:
> On 27.05.2019 14:59, Pavel Butsykin wrote:
>> This patch makes functions kpcs_req_classify() and pcs_fuse_submit() easier,
>> reducing the number of cases to handle kio requests.
>>
>> Also, this patch allows us to get rid of the additional context switch, when
>> kio request is moved to cc->work_queue list under bg_lock. After this patch,
>> execution of kpcs_req_send() is available only without fc->bg_lock.
>>
>> Signed-off-by: Pavel Butsykin <pbutsykin at virtuozzo.com>
>> ---
>>   fs/fuse/dev.c                      | 30 ++++++++-------
>>   fs/fuse/fuse_i.h                   |  2 +-
>>   fs/fuse/kio/pcs/pcs_fuse_kdirect.c | 76 +++++++++++++-------------------------
>>   3 files changed, 43 insertions(+), 65 deletions(-)
>>
>> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
>> index 3e0fecbe8db3..1ed8537b2be9 100644
>> --- a/fs/fuse/dev.c
>> +++ b/fs/fuse/dev.c
>> @@ -393,27 +393,39 @@ void fuse_queue_forget(struct fuse_conn *fc, struct fuse_forget_link *forget,
>>   
>>   static void flush_bg_queue(struct fuse_conn *fc, struct fuse_iqueue *fiq)
>>   {
>> +	struct fuse_req *req, *next;
>> +	LIST_HEAD(kio_reqs);
>> +
>>   	while (fc->active_background < fc->max_background &&
>>   	       !list_empty(&fc->bg_queue)) {
>> -		struct fuse_req *req;
>>   
>>   		req = list_first_entry(&fc->bg_queue, struct fuse_req, list);
>> -		list_del_init(&req->list);
>>   		fc->active_background++;
>>   
>>   		if (fc->kio.op) {
>>   			int ret = fc->kio.op->req_classify(fc, req, true, true);
>>   			if (likely(!ret)) {
>> -				fc->kio.op->req_send(fc, req, NULL, true, true);
>> +				list_move_tail(&req->list, &kio_reqs);
> 
> req_classify() unlocks bg_lock while req is still in bg_queue list.
> This looks as a racy design.
> 
> Also, it looks like it racy in practice with: fuse_kill_requests(..., &fc->bg_queue).
> 
> I'd remained list_del_init() in the place like we had.

Oops. Will fix.

> 
>>   				continue;
>> -			} else if (ret < 0)
>> +			} else if (ret < 0) {
>> +				list_del_init(&req->list);
>>   				continue;
>> +			}
>>   		}
>> +		list_del_init(&req->list);
>> +
>>   		spin_lock(&fiq->waitq.lock);
>>   		req->in.h.unique = fuse_get_unique(fiq);
>>   		queue_request(fiq, req);
>>   		spin_unlock(&fiq->waitq.lock);
>>   	}
>> +
>> +	spin_unlock(&fc->bg_lock);
>> +	list_for_each_entry_safe(req, next, &kio_reqs, list) {
>> +		list_del_init(&req->list);
>> +		fc->kio.op->req_send(fc, req, NULL, true);
>> +	}
>> +	spin_lock(&fc->bg_lock);
>>   }
>>   
>>   /*
>> @@ -563,7 +575,7 @@ static void __fuse_request_send(struct fuse_conn *fc, struct fuse_req *req,
>>   	if (fc->kio.op) {
>>   		int ret = fc->kio.op->req_classify(fc, req, false, false);
>>   		if (likely(!ret))
>> -			return fc->kio.op->req_send(fc, req, ff, false, false);
>> +			return fc->kio.op->req_send(fc, req, ff, false);
>>   		else if (ret < 0)
>>   			return;
>>   	}
>> @@ -656,14 +668,6 @@ void fuse_request_send_background(struct fuse_conn *fc, struct fuse_req *req)
>>   {
>>   	WARN_ON(!req->end);
>>   
>> -	if (fc->kio.op) {
>> -		int ret = fc->kio.op->req_classify(fc, req, true, false);
>> -		if (likely(!ret))
>> -			return fc->kio.op->req_send(fc, req, NULL, true, false);
>> -		else if (ret < 0)
>> -			return;
>> -	}
>> -
>>   	if (!fuse_request_queue_background(fc, req)) {
>>   		if (!req->out.h.error)
>>   			req->out.h.error = -ENOTCONN;
>> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
>> index 7978a1d891d2..34a4317a9689 100644
>> --- a/fs/fuse/fuse_i.h
>> +++ b/fs/fuse/fuse_i.h
>> @@ -530,7 +530,7 @@ struct fuse_kio_ops {
>>   	int (*req_classify)(struct fuse_conn *fc, struct fuse_req *req, bool bg,
>>   			    bool locked);
>>   	void (*req_send)(struct fuse_conn *fc, struct fuse_req *req,
>> -			 struct fuse_file *ff, bool bg, bool locked);
>> +			 struct fuse_file *ff, bool bg);
>>   
>>   	/* Inode scope hooks */
>>   	int  (*file_open)(struct fuse_conn *fc, struct file *file,
>> diff --git a/fs/fuse/kio/pcs/pcs_fuse_kdirect.c b/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
>> index a101d3950373..c15b690b0d30 100644
>> --- a/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
>> +++ b/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
>> @@ -947,7 +947,7 @@ out:
>>   }
>>   
>>   static void pcs_fuse_submit(struct pcs_fuse_cluster *pfc, struct fuse_req *req,
>> -			    struct fuse_file *ff, bool async, bool lk)
>> +			    struct fuse_file *ff)
>>   {
>>   	struct pcs_fuse_req *r = pcs_req_from_fuse(req);
>>   	struct fuse_inode *fi = get_fuse_inode(req->io_inode);
>> @@ -1040,11 +1040,7 @@ static void pcs_fuse_submit(struct pcs_fuse_cluster *pfc, struct fuse_req *req,
>>   error:
>>   	DTRACE("do fuse_request_end req:%p op:%d err:%d\n", req, req->in.h.opcode, req->out.h.error);
>>   
>> -	if (lk)
>> -		spin_unlock(&pfc->fc->bg_lock);
>>   	request_end(pfc->fc, req);
>> -	if (lk)
>> -		spin_lock(&pfc->fc->bg_lock);
>>   	return;
>>   
>>   submit:
>> @@ -1052,11 +1048,7 @@ submit:
>>   		req->out.h.error = -EIO;
>>   		goto error;
>>   	}
>> -
>> -	if (async)
>> -		pcs_cc_submit(ireq->cc, ireq);
>> -	else
>> -		ireq_process(ireq);
>> +	ireq_process(ireq);
>>   }
>>   
>>   static void kpcs_setattr_end(struct fuse_conn *fc, struct fuse_req *req)
>> @@ -1119,7 +1111,7 @@ static void _pcs_shrink_end(struct fuse_conn *fc, struct fuse_req *req)
>>   
>>   		TRACE("resubmit %p\n", &r->req);
>>   		list_del_init(&ireq->list);
>> -		pcs_fuse_submit(pfc, &r->req, r->req.ff, true, false);
>> +		pcs_fuse_submit(pfc, &r->req, r->req.ff);
>>   	}
>>   }
>>   
>> @@ -1232,64 +1224,46 @@ static int kpcs_req_classify(struct fuse_conn* fc, struct fuse_req *req,
>>   		return 1;
>>   
>>   	BUG_ON(!pfc);
>> -	/* At this point request can not belongs to any list
>> -	 * so we can avoid grab fc->lock here at all.
>> -	 */
>> -	BUG_ON(!list_empty(&req->list));
>> -
>>   	DTRACE("Classify req:%p op:%d end:%p bg:%d lk:%d\n", req, req->in.h.opcode,
>>   							  req->end, bg, lk);
>>   	ret = pcs_kio_classify_req(fc, req, lk);
>> -	if (ret) {
>> -		if (ret < 0) {
>> -			if (!bg)
>> -				atomic_inc(&req->count);
>> -			__clear_bit(FR_PENDING, &req->flags);
>> -			req->out.h.error = ret;
>> -			if (lk)
>> -				spin_unlock(&fc->bg_lock);
>> -			request_end(fc, req);
>> -			if (lk)
>> -				spin_lock(&fc->bg_lock);
>> -			return ret;
>> -		}
>> -		return 1;
>> -	}
>> +	if (likely(!ret))
>> +		return 0;
>>   
>> -	if (!lk) {
>> -		spin_lock(&fc->bg_lock);
>> -		if (fc->num_background + 1 >= fc->max_background ||
>> -		    !fc->connected) {
>> +	if (ret < 0) {
>> +		if (!bg)
>> +			atomic_inc(&req->count);
>> +		__clear_bit(FR_PENDING, &req->flags);
>> +		req->out.h.error = ret;
>> +		if (lk)
>>   			spin_unlock(&fc->bg_lock);
>> -			return 1;
>> -		}
>> -		fc->num_background++;
>> -		fc->active_background++;
>> -
>> -		if (fc->num_background == fc->congestion_threshold &&
>> -		    fc->bdi_initialized) {
>> -			set_bdi_congested(&fc->bdi, BLK_RW_SYNC);
>> -			set_bdi_congested(&fc->bdi, BLK_RW_ASYNC);
>> -		}
>> -		spin_unlock(&fc->bg_lock);
>> +		request_end(fc, req);
>> +		if (lk)
>> +			spin_lock(&fc->bg_lock);
>> +		return ret;
>>   	}
>> -       return 0;
>> +	return 1;
>>   }
>>   
>>   static void kpcs_req_send(struct fuse_conn* fc, struct fuse_req *req,
>> -			  struct fuse_file *ff, bool bg, bool lk)
>> +			  struct fuse_file *ff, bool bg)
>>   {
>>          struct pcs_fuse_cluster *pfc = (struct pcs_fuse_cluster*)fc->kio.ctx;
>>   
>> -       TRACE("Send req:%p op:%d end:%p bg:%d lk:%d\n",
>> -               req, req->in.h.opcode, req->end, bg, lk);
>> +       /* At this point request can not belongs to any list
>> +        * so we can avoid grab fc->lock here at all.
>> +        */
>> +       BUG_ON(!list_empty(&req->list));
>> +
>> +       TRACE("Send req:%p op:%d end:%p bg:%d\n",
>> +               req, req->in.h.opcode, req->end, bg);
>>   
>>          /* request_end below will do fuse_put_request() */
>>          if (!bg)
>>                  atomic_inc(&req->count);
>>   	__clear_bit(FR_PENDING, &req->flags);
>>   
>> -	pcs_fuse_submit(pfc, req, ff ? : req->ff, lk, lk);
>> +	pcs_fuse_submit(pfc, req, ff ? : req->ff);
>>   	if (!bg)
>>   		wait_event(req->waitq,
>>   			   test_bit(FR_FINISHED, &req->flags) && !req->end);
>>
> 



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