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SubjectRe: [PATCH 20/20] fuse,virtiofs: Add logic to free up a memory range
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.

> 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)
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