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SubjectRe: [PATCH 20/20] fuse,virtiofs: Add logic to free up a memory range
On Wed, Mar 11, 2020 at 08:59:23AM -0400, Vivek Goyal wrote:
> On Wed, Mar 11, 2020 at 01:16:42PM +0800, Liu Bo wrote:
>
> [..]
> > > @@ -719,6 +723,7 @@ void fuse_conn_put(struct fuse_conn *fc)
> > > if (refcount_dec_and_test(&fc->count)) {
> > > struct fuse_iqueue *fiq = &fc->iq;
> > >
> > > + flush_delayed_work(&fc->dax_free_work);
> >
> > Today while debugging another case, I realized that flushing work here
> > at the very last fuse_conn_put() is a bit too late, here's my analysis,
> >
> > umount kthread
> >
> > deactivate_locked_super
> > ->virtio_kill_sb try_to_free_dmap_chunks
> > ->generic_shutdown_super ->igrab()
> > ...
> > ->evict_inodes() -> check all inodes' count
> > ->fuse_conn_put ->iput
> > ->virtio_fs_free_devs
> > ->fuse_dev_free
> > ->fuse_conn_put // vq1
> > ->fuse_dev_free
> > ->fuse_conn_put // vq2
> > ->flush_delayed_work
> >
> > The above can end up with a warning message reported by evict_inodes()
> > about stable inodes.
>
> Hi Liu Bo,
>
> Which warning is that? Can you point me to it in code.
>

Hmm, it was actually in generic_shutdow_super,
---
printk("VFS: Busy inodes after unmount of %s. "
"Self-destruct in 5 seconds. Have a nice day...\n",
---

> > So I think it's necessary to put either
> > cancel_delayed_work_sync() or flush_delayed_work() before going to
> > generic_shutdown_super().
>
> In general I agree that shutting down memory range freeing worker
> earling in unmount/shutdown sequence makes sense. It does not seem
> to help to let it run while filesystem is going away. How about following
> patch.
>
> ---
> fs/fuse/inode.c | 1 -
> fs/fuse/virtio_fs.c | 5 +++++
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> Index: redhat-linux/fs/fuse/virtio_fs.c
> ===================================================================
> --- redhat-linux.orig/fs/fuse/virtio_fs.c 2020-03-10 14:11:10.970284651 -0400
> +++ redhat-linux/fs/fuse/virtio_fs.c 2020-03-11 08:27:08.103330039 -0400
> @@ -1295,6 +1295,11 @@ static void virtio_kill_sb(struct super_
> vfs = fc->iq.priv;
> fsvq = &vfs->vqs[VQ_HIPRIO];
>
> + /* Stop dax worker. Soon evict_inodes() will be called which will
> + * free all memory ranges belonging to all inodes.
> + */
> + flush_delayed_work(&fc->dax_free_work);
> +
> /* Stop forget queue. Soon destroy will be sent */
> spin_lock(&fsvq->lock);
> fsvq->connected = false;
> Index: redhat-linux/fs/fuse/inode.c
> ===================================================================
> --- redhat-linux.orig/fs/fuse/inode.c 2020-03-10 09:13:35.132565666 -0400
> +++ redhat-linux/fs/fuse/inode.c 2020-03-11 08:22:02.685330039 -0400
> @@ -723,7 +723,6 @@ void fuse_conn_put(struct fuse_conn *fc)
> if (refcount_dec_and_test(&fc->count)) {
> struct fuse_iqueue *fiq = &fc->iq;
>
> - flush_delayed_work(&fc->dax_free_work);
> if (fc->dax_dev)
> fuse_free_dax_mem_ranges(&fc->free_ranges);
> if (fiq->ops->release)

Looks good, it should be safe now, but I feel like
cancel_delayed_work_sync() would be a good alternative for "stop dax
worker".

Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>

Fine with either folding directly or a new patch, thanks for fixing it.

thanks,
-liubo

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