Merge tag 'fuse-update-5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse

Pull fuse updates from Miklos Szeredi:

 - Support directly accessing host page cache from virtiofs. This can
   improve I/O performance for various workloads, as well as reducing
   the memory requirement by eliminating double caching. Thanks to Vivek
   Goyal for doing most of the work on this.

 - Allow automatic submounting inside virtiofs. This allows unique
   st_dev/ st_ino values to be assigned inside the guest to files
   residing on different filesystems on the host. Thanks to Max Reitz
   for the patches.

 - Fix an old use after free bug found by Pradeep P V K.

* tag 'fuse-update-5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse: (25 commits)
  virtiofs: calculate number of scatter-gather elements accurately
  fuse: connection remove fix
  fuse: implement crossmounts
  fuse: Allow fuse_fill_super_common() for submounts
  fuse: split fuse_mount off of fuse_conn
  fuse: drop fuse_conn parameter where possible
  fuse: store fuse_conn in fuse_req
  fuse: add submount support to <uapi/linux/fuse.h>
  fuse: fix page dereference after free
  virtiofs: add logic to free up a memory range
  virtiofs: maintain a list of busy elements
  virtiofs: serialize truncate/punch_hole and dax fault path
  virtiofs: define dax address space operations
  virtiofs: add DAX mmap support
  virtiofs: implement dax read/write operations
  virtiofs: introduce setupmapping/removemapping commands
  virtiofs: implement FUSE_INIT map_alignment field
  virtiofs: keep a list of free dax memory ranges
  virtiofs: add a mount option to enable dax
  virtiofs: set up virtio_fs dax_device
  ...

1 files changed, 15 insertions, 5 deletions

diff --git a/fs/fuse/control.c b/fs/fuse/control.c
index a1303ad303ba..cc7e94d73c6c 100644
--- a/fs/fuse/control.c
+++ b/fs/fuse/control.c
@@ -164,6 +164,7 @@ static ssize_t fuse_conn_congestion_threshold_write(struct file *file,
 {
 	unsigned val;
 	struct fuse_conn *fc;
+	struct fuse_mount *fm;
 	ssize_t ret;
 
 	ret = fuse_conn_limit_write(file, buf, count, ppos, &val,
@@ -174,18 +175,27 @@ static ssize_t fuse_conn_congestion_threshold_write(struct file *file,
 	if (!fc)
 		goto out;
 
+	down_read(&fc->killsb);
 	spin_lock(&fc->bg_lock);
 	fc->congestion_threshold = val;
-	if (fc->sb) {
+
+	/*
+	 * Get any fuse_mount belonging to this fuse_conn; s_bdi is
+	 * shared between all of them
+	 */
+
+	if (!list_empty(&fc->mounts)) {
+		fm = list_first_entry(&fc->mounts, struct fuse_mount, fc_entry);
 		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);
+			clear_bdi_congested(fm->sb->s_bdi, BLK_RW_SYNC);
+			clear_bdi_congested(fm->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);
+			set_bdi_congested(fm->sb->s_bdi, BLK_RW_SYNC);
+			set_bdi_congested(fm->sb->s_bdi, BLK_RW_ASYNC);
 		}
 	}
 	spin_unlock(&fc->bg_lock);
+	up_read(&fc->killsb);
 	fuse_conn_put(fc);
 out:
 	return ret;