[Devel] [PATCH 3/8] fuse: do not take fc->lock in fuse_request_send_background()

[Pavel Butsykin]

On 03.04.2019 18:37, Kirill Tkhai wrote:
> ms commit 63825b4e1da5
> 
> Currently, we take fc->lock there only to check for fc->connected.
> But this flag is changed only on connection abort, which is very
> rare operation.
> 
> So allow checking fc->connected under just fc->bg_lock and use this lock
> (as well as fc->lock) when resetting fc->connected.
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> Signed-off-by: Miklos Szeredi <mszeredi at redhat.com>
> ---
>   fs/fuse/dev.c    |   73 +++++++++++++++++++++++++++---------------------------
>   fs/fuse/file.c   |    4 ++-
>   fs/fuse/fuse_i.h |    3 +-
>   3 files changed, 41 insertions(+), 39 deletions(-)
> 
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 1ffc10ff18ba..1355f4a0a8e4 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -598,69 +598,70 @@ void fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
>   }
>   EXPORT_SYMBOL_GPL(fuse_request_send);
>   
> -/*
> - * Called under fc->lock
> - *
> - * fc->connected must have been checked previously
> - */
> -void fuse_request_send_background_nocheck(struct fuse_conn *fc,
> -					  struct fuse_req *req)
> +bool fuse_request_queue_background(struct fuse_conn *fc, struct fuse_req *req)
>   {
>   	struct fuse_iqueue *fiq = req->fiq;
> +	bool queued = false;
>   
> -	BUG_ON(!test_bit(FR_BACKGROUND, &req->flags));
> -
> +	WARN_ON(!test_bit(FR_BACKGROUND, &req->flags));
>   	if (!test_bit(FR_WAITING, &req->flags)) {
>   		__set_bit(FR_WAITING, &req->flags);
>   		atomic_inc(&fc->num_waiting);
>   	}
>   	__set_bit(FR_ISREPLY, &req->flags);
>   	spin_lock(&fc->bg_lock);
> -	fc->num_background++;
> -	if (fc->num_background == fc->max_background)
> -		fc->blocked = 1;
> -	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);
> -	}
> +	if (likely(fc->connected)) {
> +		fc->num_background++;
> +		if (fc->num_background == fc->max_background)
> +			fc->blocked = 1;
> +		if (fc->num_background == fc->congestion_threshold && fc->sb) {
> +			set_bdi_congested(fc->sb->s_bdi, BLK_RW_SYNC);
> +			set_bdi_congested(fc->sb->s_bdi, BLK_RW_ASYNC);
> +		}
>   
> -	if (test_bit(FR_NONBLOCKING, &req->flags)) {
> -		fc->active_background++;
> -		spin_lock(&fiq->waitq.lock);
> -		req->in.h.unique = fuse_get_unique(fiq);
> -		queue_request(fiq, req);
> -		spin_unlock(&fiq->waitq.lock);
> -		goto unlock;
> -	}
> +		if (test_bit(FR_NONBLOCKING, &req->flags)) {
> +			fc->active_background++;
> +			spin_lock(&fiq->waitq.lock);
> +			req->in.h.unique = fuse_get_unique(fiq);
> +			queue_request(fiq, req);
> +			spin_unlock(&fiq->waitq.lock);
> +			queued = true;
> +			goto unlock;
> +		}
>   
> -	list_add_tail(&req->list, &fc->bg_queue);
> -	flush_bg_queue(fc, fiq);
> +		list_add_tail(&req->list, &fc->bg_queue);
> +		flush_bg_queue(fc, fiq);
> +		queued = true;
> +        }
>   unlock:
>   	spin_unlock(&fc->bg_lock);
> +	return queued;
>   }
>   
>   void fuse_request_send_background(struct fuse_conn *fc, struct fuse_req *req)
>   {
> -	BUG_ON(!req->end);
> +	bool fail;
> +	WARN_ON(!req->end);
>   
>   	if (fc->kio.op && !fc->kio.op->req_send(fc, req, true, false))
>   		return;
>   
>   	spin_lock(&fc->lock);
> -	if (req->page_cache && req->ff &&
> -	    test_bit(FUSE_S_FAIL_IMMEDIATELY, &req->ff->ff_state)) {
> +	fail = (req->page_cache && req->ff &&
> +		test_bit(FUSE_S_FAIL_IMMEDIATELY, &req->ff->ff_state));
> +	spin_unlock(&fc->lock);
> +
> +	if (fail) {
> +		/* FIXME */

What needs to be fixed here?

>   		BUG_ON(req->in.h.opcode != FUSE_READ);
>   		req->out.h.error = -EIO;
>   		__clear_bit(FR_BACKGROUND, &req->flags);
>   		__clear_bit(FR_PENDING, &req->flags);
> -		spin_unlock(&fc->lock);
>   		request_end(fc, req);
> -	} else if (fc->connected) {
> -		fuse_request_send_background_nocheck(fc, req);
> -		spin_unlock(&fc->lock);
> -	} else {
> -		spin_unlock(&fc->lock);
> +		return;
> +	}
> +
> +	if (!fuse_request_queue_background(fc, req)) {
>   		req->out.h.error = -ENOTCONN;
>   		req->end(fc, req);
>   		fuse_put_request(fc, req);
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index edc314bd7156..6bffa1eef4dd 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -1941,6 +1941,7 @@ __acquires(fc->lock)
>   	loff_t size = i_size_read(req->inode);
>   	struct fuse_write_in *inarg = &req->misc.write.in;
>   	__u64 data_size = req->num_pages * PAGE_CACHE_SIZE;
> +	bool queued;
>   
>   	if (!fc->connected ||
>   	    test_bit(FUSE_S_FAIL_IMMEDIATELY, &req->ff->ff_state))
> @@ -1957,7 +1958,8 @@ __acquires(fc->lock)
>   
>   	req->in.args[1].size = inarg->size;
>   	fi->writectr++;
> -	fuse_request_send_background_nocheck(fc, req);
> +	queued = fuse_request_queue_background(fc, req);
> +	WARN_ON(!queued);
>   	return;
>   
>    out_free:
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index a6eb566f8789..ee8b367f2956 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -979,8 +979,7 @@ void fuse_request_check_and_send(struct fuse_conn *fc, struct fuse_req *req,
>    */
>   void fuse_request_send_background(struct fuse_conn *fc, struct fuse_req *req);
>   
> -void fuse_request_send_background_nocheck(struct fuse_conn *fc,
> -					  struct fuse_req *req);
> +bool fuse_request_queue_background(struct fuse_conn *fc, struct fuse_req *req);
>   
>   /* Abort all requests */
>   void fuse_abort_conn(struct fuse_conn *fc);
>