On Mon, Aug 10, 2020 at 10:29:13AM +0200, Miklos Szeredi wrote: > On Fri, Aug 7, 2020 at 9:55 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > > > fuse_file_put(sync) can be called with sync=true/false. If sync=true, > > it waits for release request response and then calls iput() in the > > caller's context. If sync=false, it does not wait for release request > > response, frees the fuse_file struct immediately and req->end function > > does the iput(). > > > > iput() can be a problem with DAX if called in req->end context. If this > > is last reference to inode (VFS has let go its reference already), then > > iput() will clean DAX mappings as well and send REMOVEMAPPING requests > > and wait for completion. (All the the worker thread context which is > > processing fuse replies from daemon on the host). > > > > That means it blocks worker thread and it stops processing further > > replies and system deadlocks. > > Is this reasoning specific to DAX? Seems to me this is a virtio-fs > specific issue. I would think it is virtio-fs + DAX issues. virtio-fs without DAX does not have this problem. If making this conditional on DAX an issue, I am wondering, can we now set args->may_block instead. Now virtiofs will do completion in a separate worker thread if ->may_block is set. That means, worker will block till REMOVEMAPPING completes and then be woken up. Do let me know if you like setting args->may_block approach better. I can give that a try. Vivek
