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From: Amir Goldstein <amir73il@gmail.com>
To: Christian Brauner <brauner@kernel.org>, Jeff Layton <jlayton@kernel.org>
Cc: Josef Bacik <josef@toxicpanda.com>,
	Christoph Hellwig <hch@lst.de>, Jan Kara <jack@suse.cz>,
	 David Howells <dhowells@redhat.com>,
	Jens Axboe <axboe@kernel.dk>,  Miklos Szeredi <miklos@szeredi.hu>,
	Al Viro <viro@zeniv.linux.org.uk>,
	 linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 0/2] Avert possible deadlock with splice() and fanotify
Date: Thu, 30 Nov 2023 10:32:49 +0200	[thread overview]
Message-ID: <CAOQ4uxhCC+ZpULkBf_WfsyRBToNxksesBAk5nCsGYWkuNFu6JA@mail.gmail.com> (raw)
In-Reply-To: <20231129200709.3154370-1-amir73il@gmail.com>

On Wed, Nov 29, 2023 at 10:07 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> Christian,
>
> Josef has helped me see the light and figure out how to avoid the
> possible deadlock, which involves:
> - splice() from source file in a loop mounted fs to dest file in
>   a host fs, where the loop image file is
> - fsfreeze on host fs
> - write to host fs in context of fanotify permission event handler
>   (FAN_ACCESS_PERM) on the splice source file
>
> The first patch should not be changing any logic.
> I only build tested the ceph patch, so hoping to get an
> Acked-by/Tested-by from Jeff.
>
> The second patch rids us of the deadlock by not holding
> file_start_write() while reading from splice source file.
>

OOPS, I missed another corner case:
The COPY_FILE_SPLICE fallback of server-side-copy in nfsd/ksmbd
needs to use the start-write-safe variant of do_splice_direct(),
because in this case src and dst can be on any two fs.
Expect an extra patch in v2.

Thanks,
Amir.

  parent reply	other threads:[~2023-11-30  8:33 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-29 20:07 [PATCH 0/2] Avert possible deadlock with splice() and fanotify Amir Goldstein
2023-11-29 20:07 ` [PATCH 1/2] fs: fork do_splice_copy_file_range() from do_splice_direct() Amir Goldstein
2023-11-30 10:09   ` Amir Goldstein
2023-11-30 13:30     ` Jan Kara
2023-11-30 13:18   ` Christian Brauner
2023-11-30 13:37     ` Amir Goldstein
2023-11-29 20:07 ` [PATCH 2/2] fs: move file_start_write() into direct_splice_actor() Amir Goldstein
2023-11-30 13:32   ` Jan Kara
2023-11-30  8:32 ` Amir Goldstein [this message]
2023-11-30 10:07   ` [PATCH 0/2] Avert possible deadlock with splice() and fanotify Amir Goldstein
2023-11-30 13:37     ` Jan Kara
2023-11-30 13:46       ` Amir Goldstein

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