From: Miklos Szeredi <miklos@szeredi.hu>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
virtio-fs-list <virtio-fs@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: [PATCH v2 18/20] fuse: Release file in process context
Date: Mon, 10 Aug 2020 21:39:46 +0200 [thread overview]
Message-ID: <CAJfpegsARKo+az+4Q98ecH3RMQinFT=QeMdte2=aZdvbz2WY1w@mail.gmail.com> (raw)
In-Reply-To: <20200810193717.GF455528@redhat.com>
On Mon, Aug 10, 2020 at 9:37 PM Vivek Goyal <vgoyal@redhat.com> wrote:
>
> 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@redhat.com> 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.
>
> Hi Miklos,
>
> I am looking at this patch closely and maybe we don't need it, given
> current code.
>
> Reason being that looks like for virtiofs now we set ctx->destroy=true
> and that sets fc->destroy. And if that's set, we don't schedule async req
> in fuse_release_common();
>
> fuse_release_common() {
> fuse_file_put(ff, ff->fc->destroy, isdir);
> }
>
> And if we don't schedule async file put, we don't run the risk of
> blocking worker thread in evict_inode() with DAX enabled.
>
> I ran blogbench multiple times with this patch reverted and I can't
> reproduce the deadlock.
>
> So we can drop this patch for now. If need be I will fix it as
> post merge patch.
Okay. Yeah, I was thinking along the lines of no-async-release-ever
for virtiofs, but apparently that's already done.
Thanks,
Miklos
next prev parent reply other threads:[~2020-08-10 19:40 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-07 19:55 [PATCH v2 00/20] virtiofs: Add DAX support Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 01/20] dax: Modify bdev_dax_pgoff() to handle NULL bdev Vivek Goyal
2020-08-17 16:57 ` Jan Kara
2020-08-07 19:55 ` [PATCH v2 02/20] dax: Create a range version of dax_layout_busy_page() Vivek Goyal
2020-08-17 16:53 ` Jan Kara
2020-08-17 17:22 ` Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 03/20] virtio: Add get_shm_region method Vivek Goyal
2020-08-10 13:47 ` Michael S. Tsirkin
2020-08-10 13:54 ` Vivek Goyal
2020-08-10 14:02 ` Michael S. Tsirkin
2020-08-10 14:06 ` Michael S. Tsirkin
2020-08-07 19:55 ` [PATCH v2 04/20] virtio: Implement get_shm_region for PCI transport Vivek Goyal
2020-08-10 14:05 ` Michael S. Tsirkin
2020-08-10 14:50 ` Vivek Goyal
[not found] ` <CAAfnVBk+Hmcm2ftd3wOK-P2NyYQ7z4Wrf1JKhLJaNkCZBLoo6g@mail.gmail.com>
2020-08-17 20:29 ` Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 05/20] virtio: Implement get_shm_region for MMIO transport Vivek Goyal
2020-08-10 14:03 ` Michael S. Tsirkin
2020-08-07 19:55 ` [PATCH v2 06/20] virtiofs: Provide a helper function for virtqueue initialization Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 07/20] fuse: Get rid of no_mount_options Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 08/20] fuse,virtiofs: Add a mount option to enable dax Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 09/20] virtio_fs, dax: Set up virtio_fs dax_device Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 10/20] fuse,virtiofs: Keep a list of free dax memory ranges Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 11/20] fuse: implement FUSE_INIT map_alignment field Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 12/20] fuse: Introduce setupmapping/removemapping commands Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 13/20] fuse, dax: Implement dax read/write operations Vivek Goyal
2020-08-10 22:06 ` Dave Chinner
2020-08-11 17:44 ` Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 14/20] fuse,dax: add DAX mmap support Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 15/20] fuse, dax: Take ->i_mmap_sem lock during dax page fault Vivek Goyal
2020-08-10 22:22 ` Dave Chinner
2020-08-11 17:55 ` Vivek Goyal
2020-08-12 1:23 ` Dave Chinner
2020-08-12 21:10 ` Vivek Goyal
2020-08-13 5:12 ` Dave Chinner
2020-08-07 19:55 ` [PATCH v2 16/20] fuse,virtiofs: Define dax address space operations Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 17/20] fuse,virtiofs: Maintain a list of busy elements Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 18/20] fuse: Release file in process context Vivek Goyal
2020-08-10 8:29 ` Miklos Szeredi
2020-08-10 15:48 ` Vivek Goyal
2020-08-10 19:37 ` Vivek Goyal
2020-08-10 19:39 ` Miklos Szeredi [this message]
2020-08-07 19:55 ` [PATCH v2 19/20] fuse: Take inode lock for dax inode truncation Vivek Goyal
2020-08-07 19:55 ` [PATCH v2 20/20] fuse,virtiofs: Add logic to free up a memory range Vivek Goyal
2020-08-10 7:29 ` [PATCH v2 00/20] virtiofs: Add DAX support Miklos Szeredi
2020-08-10 13:08 ` Vivek Goyal
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