On Fri, Sep 06, 2019 at 09:51:31AM -0400, Vivek Goyal wrote:
> On Fri, Sep 06, 2019 at 01:05:34PM +0100, Stefan Hajnoczi wrote:
> > On Thu, Sep 05, 2019 at 03:48:57PM -0400, Vivek Goyal wrote:
> > > It is possible that a mount is in progress and device is being removed at
> > > the same time. Use virtio_fs_mutex to avoid races.
> > >
> > > This also takes care of bunch of races and removes some TODO items.
> > >
> > > Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> > > ---
> > > fs/fuse/virtio_fs.c | 32 ++++++++++++++++++++++----------
> > > 1 file changed, 22 insertions(+), 10 deletions(-)
> >
> > Let's move to a per-device mutex in the future. That way a single
> > device that fails to drain/complete requests will not hang all other
> > virtio-fs instances. This is fine for now.
>
> Good point. For now I updated the patch so that it applies cleanly
> after previous two patches changed.
>
> Subject: virtiofs: Use virtio_fs_mutex for races w.r.t ->remove and mount path
>
> It is possible that a mount is in progress and device is being removed at
> the same time. Use virtio_fs_mutex to avoid races.
>
> This also takes care of bunch of races and removes some TODO items.
>
> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> ---
> fs/fuse/virtio_fs.c | 32 ++++++++++++++++++++++----------
> 1 file changed, 22 insertions(+), 10 deletions(-)
>
> Index: rhvgoyal-linux-fuse/fs/fuse/virtio_fs.c
> ===================================================================
> --- rhvgoyal-linux-fuse.orig/fs/fuse/virtio_fs.c 2019-09-06 09:40:53.309245246 -0400
> +++ rhvgoyal-linux-fuse/fs/fuse/virtio_fs.c 2019-09-06 09:43:25.335245246 -0400
> @@ -13,7 +13,9 @@
> #include <linux/highmem.h>
> #include "fuse_i.h"
>
> -/* List of virtio-fs device instances and a lock for the list */
> +/* List of virtio-fs device instances and a lock for the list. Also provides
> + * mutual exclusion in device removal and mounting path
> + */
> static DEFINE_MUTEX(virtio_fs_mutex);
> static LIST_HEAD(virtio_fs_instances);
>
> @@ -72,17 +74,19 @@ static void release_virtio_fs_obj(struct
> kfree(vfs);
> }
>
> +/* Make sure virtiofs_mutex is held */
> static void virtio_fs_put(struct virtio_fs *fs)
> {
> - mutex_lock(&virtio_fs_mutex);
> kref_put(&fs->refcount, release_virtio_fs_obj);
> - mutex_unlock(&virtio_fs_mutex);
> }
>
> static void virtio_fs_fiq_release(struct fuse_iqueue *fiq)
> {
> struct virtio_fs *vfs = fiq->priv;
> +
> + mutex_lock(&virtio_fs_mutex);
> virtio_fs_put(vfs);
> + mutex_unlock(&virtio_fs_mutex);
> }
>
> static void virtio_fs_drain_queue(struct virtio_fs_vq *fsvq)
> @@ -596,9 +600,8 @@ static void virtio_fs_remove(struct virt
> struct virtio_fs *fs = vdev->priv;
>
> mutex_lock(&virtio_fs_mutex);
> + /* This device is going away. No one should get new reference */
> list_del_init(&fs->list);
> - mutex_unlock(&virtio_fs_mutex);
> -
> virtio_fs_stop_all_queues(fs);
> virtio_fs_drain_all_queues(fs);
> vdev->config->reset(vdev);
> @@ -607,6 +610,7 @@ static void virtio_fs_remove(struct virt
> vdev->priv = NULL;
> /* Put device reference on virtio_fs object */
> virtio_fs_put(fs);
> + mutex_unlock(&virtio_fs_mutex);
> }
>
> #ifdef CONFIG_PM_SLEEP
> @@ -978,10 +982,15 @@ static int virtio_fs_fill_super(struct s
> .no_force_umount = true,
> };
>
> - /* TODO lock */
> - if (fs->vqs[VQ_REQUEST].fud) {
> - pr_err("virtio-fs: device already in use\n");
> - err = -EBUSY;
> + mutex_lock(&virtio_fs_mutex);
> +
> + /* After holding mutex, make sure virtiofs device is still there.
> + * Though we are holding a refernce to it, drive ->remove might
> + * still have cleaned up virtual queues. In that case bail out.
> + */
> + err = -EINVAL;
> + if (list_empty(&fs->list)) {
> + pr_info("virtio-fs: tag <%s> not found\n", fs->tag);
> goto err;
> }
>
> @@ -1007,7 +1016,6 @@ static int virtio_fs_fill_super(struct s
>
> fc = fs->vqs[VQ_REQUEST].fud->fc;
>
> - /* TODO take fuse_mutex around this loop? */
> for (i = 0; i < fs->nvqs; i++) {
> struct virtio_fs_vq *fsvq = &fs->vqs[i];
>
> @@ -1020,6 +1028,7 @@ static int virtio_fs_fill_super(struct s
> /* Previous unmount will stop all queues. Start these again */
> virtio_fs_start_all_queues(fs);
> fuse_send_init(fc, init_req);
> + mutex_unlock(&virtio_fs_mutex);
> return 0;
>
> err_free_init_req:
> @@ -1027,6 +1036,7 @@ err_free_init_req:
> err_free_fuse_devs:
> virtio_fs_free_devs(fs);
> err:
> + mutex_unlock(&virtio_fs_mutex);
> return err;
> }
>
> @@ -1100,7 +1110,9 @@ static int virtio_fs_get_tree(struct fs_
>
> fc = kzalloc(sizeof(struct fuse_conn), GFP_KERNEL);
> if (!fc) {
> + mutex_lock(&virtio_fs_mutex);
> virtio_fs_put(fs);
> + mutex_unlock(&virtio_fs_mutex);
> return -ENOMEM;
> }
>
>
Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
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