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From: Vivek Goyal <vgoyal@redhat.com>
To: Miklos Szeredi <miklos@szeredi.hu>
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 11:48:30 -0400	[thread overview]
Message-ID: <20200810154830.GC455528@redhat.com> (raw)
In-Reply-To: <CAJfpegs1CtPMaVmbDc__N0Fc3FkNEe=vQOkrr8RKiiS6NqTyHA@mail.gmail.com>

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.

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


  reply	other threads:[~2020-08-10 15:48 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 [this message]
2020-08-10 19:37     ` Vivek Goyal
2020-08-10 19:39       ` Miklos Szeredi
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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