fuse: add locking to max_background and congestion_threshold changes

Functions sequences like request_end()->flush_bg_queue() require that
max_background and congestion_threshold are constant during their
execution. Otherwise, checks like

	if (fc->num_background == fc->max_background)

made in different time may behave not like expected.

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

1 files changed, 24 insertions, 6 deletions

diff --git a/fs/fuse/control.c b/fs/fuse/control.c
index acc35819aae6..eaa0e2b21623 100644
--- a/fs/fuse/control.c
+++ b/fs/fuse/control.c
@@ -125,7 +125,12 @@ static ssize_t fuse_conn_max_background_write(struct file *file,
         if (ret > 0) {
                 struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
                 if (fc) {
+                        spin_lock(&fc->lock);
                         fc->max_background = val;
+                        fc->blocked = fc->num_background >= fc->max_background;
+                        if (!fc->blocked)
+                                wake_up(&fc->blocked_waitq);
+                        spin_unlock(&fc->lock);
                         fuse_conn_put(fc);
                 }
         }
@@ -155,18 +160,31 @@ static ssize_t fuse_conn_congestion_threshold_write(struct file *file,
                                                     size_t count, loff_t *ppos)
 {
         unsigned uninitialized_var(val);
+        struct fuse_conn *fc;
         ssize_t ret;
 
         ret = fuse_conn_limit_write(file, buf, count, ppos, &val,
                                     max_user_congthresh);
-        if (ret > 0) {
-                struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
-                if (fc) {
-                        fc->congestion_threshold = val;
-                        fuse_conn_put(fc);
+        if (ret <= 0)
+                goto out;
+        fc = fuse_ctl_file_conn_get(file);
+        if (!fc)
+                goto out;
+
+        spin_lock(&fc->lock);
+        fc->congestion_threshold = val;
+        if (fc->sb) {
+                if (fc->num_background < fc->congestion_threshold) {
+                        clear_bdi_congested(fc->sb->s_bdi, BLK_RW_SYNC);
+                        clear_bdi_congested(fc->sb->s_bdi, BLK_RW_ASYNC);
+                } else {
+                        set_bdi_congested(fc->sb->s_bdi, BLK_RW_SYNC);
+                        set_bdi_congested(fc->sb->s_bdi, BLK_RW_ASYNC);
                 }
         }
-
+        spin_unlock(&fc->lock);
+        fuse_conn_put(fc);
+out:
         return ret;
 }