fuse: do not take fc->lock in fuse_request_send_background()

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@virtuozzo.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

3 files changed, 28 insertions, 28 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index d4b9ffc6544d..071feb8cb265 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -581,42 +581,38 @@ ssize_t fuse_simple_request(struct fuse_conn *fc, struct fuse_args *args)
         return ret;
 }
 
-/*
- * 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)
 {
-        BUG_ON(!test_bit(FR_BACKGROUND, &req->flags));
+        bool queued = false;
+
+        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->sb) {
-                set_bdi_congested(fc->sb->s_bdi, BLK_RW_SYNC);
-                set_bdi_congested(fc->sb->s_bdi, BLK_RW_ASYNC);
-        }
-        list_add_tail(&req->list, &fc->bg_queue);
-        flush_bg_queue(fc);
+        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);
+                }
+                list_add_tail(&req->list, &fc->bg_queue);
+                flush_bg_queue(fc);
+                queued = true;
+        }
         spin_unlock(&fc->bg_lock);
+
+        return queued;
 }
 
 void fuse_request_send_background(struct fuse_conn *fc, struct fuse_req *req)
 {
-        BUG_ON(!req->end);
-        spin_lock(&fc->lock);
-        if (fc->connected) {
-                fuse_request_send_background_nocheck(fc, req);
-                spin_unlock(&fc->lock);
-        } else {
-                spin_unlock(&fc->lock);
+        WARN_ON(!req->end);
+        if (!fuse_request_queue_background(fc, req)) {
                 req->out.h.error = -ENOTCONN;
                 req->end(fc, req);
                 fuse_put_request(fc, req);
@@ -2119,7 +2115,11 @@ void fuse_abort_conn(struct fuse_conn *fc, bool is_abort)
                 struct fuse_req *req, *next;
                 LIST_HEAD(to_end);
 
+                /* Background queuing checks fc->connected under bg_lock */
+                spin_lock(&fc->bg_lock);
                 fc->connected = 0;
+                spin_unlock(&fc->bg_lock);
+
                 fc->aborted = is_abort;
                 fuse_set_initialized(fc);
                 list_for_each_entry(fud, &fc->devices, entry) {
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 65351d43c2b6..d15c14912e72 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1487,6 +1487,7 @@ __acquires(fc->lock)
         struct fuse_inode *fi = get_fuse_inode(req->inode);
         struct fuse_write_in *inarg = &req->misc.write.in;
         __u64 data_size = req->num_pages * PAGE_SIZE;
+        bool queued;
 
         if (!fc->connected)
                 goto out_free;
@@ -1502,7 +1503,8 @@ __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 d6d55641a5a6..6e6eab8127a4 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -863,9 +863,7 @@ ssize_t fuse_simple_request(struct fuse_conn *fc, struct fuse_args *args);
  * Send a request in the background
  */
 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, bool is_abort);