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From: Matthew Wilcox <willy@infradead.org>
To: Jeff Layton <jlayton@kernel.org>
Cc: Amir Goldstein <amir73il@gmail.com>,
	Sargun Dhillon <sargun@sargun.me>,
	Vivek Goyal <vgoyal@redhat.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	Miklos Szeredi <miklos@szeredi.hu>, Jan Kara <jack@suse.cz>,
	NeilBrown <neilb@suse.com>, Al Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@lst.de>,
	Chengguang Xu <cgxu519@mykernel.net>
Subject: Re: [PATCH 3/3] overlayfs: Report writeback errors on upper
Date: Mon, 28 Dec 2020 15:56:18 +0000	[thread overview]
Message-ID: <20201228155618.GA6211@casper.infradead.org> (raw)
In-Reply-To: <1334bba9cefa81f80005f8416680afb29044379c.camel@kernel.org>

On Mon, Dec 28, 2020 at 08:25:50AM -0500, Jeff Layton wrote:
> To be clear, the main thing you'll lose with the method above is the
> ability to see an unseen error on a newly opened fd, if there was an
> overlayfs mount using the same upper sb before your open occurred.
> 
> IOW, consider two overlayfs mounts using the same upper layer sb:
> 
> ovlfs1				ovlfs2
> ----------------------------------------------------------------------
> mount
> open fd1
> write to fd1
> <writeback fails>
> 				mount (upper errseq_t SEEN flag marked)
> open fd2
> syncfs(fd2)
> syncfs(fd1)
> 
> 
> On a "normal" (non-overlay) fs, you'd get an error back on both syncfs
> calls. The first one has a sample from before the error occurred, and
> the second one has a sample of 0, due to the fact that the error was
> unseen at open time.
> 
> On overlayfs, with the intervening mount of ovlfs2, syncfs(fd1) will
> return an error and syncfs(fd2) will not. If we split the SEEN flag into
> two, then we can ensure that they both still get an error in this
> situation.

But do we need to?  If the inode has been evicted we also lose the errno.
The guarantee we provide is that a fd that was open before the error
occurred will see the error.  An fd that's opened after the error occurred
may or may not see the error.


  parent reply	other threads:[~2020-12-28 15:58 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-21 19:50 [RFC PATCH 0/3][v3] vfs, overlayfs: Fix syncfs() to return correct errors Vivek Goyal
2020-12-21 19:50 ` [PATCH 1/3] vfs: Do not ignore return code from s_op->sync_fs Vivek Goyal
2020-12-22  1:23   ` NeilBrown
2020-12-22 15:17     ` Vivek Goyal
2020-12-21 19:50 ` [PATCH 2/3] vfs: Add a super block operation to check for writeback errors Vivek Goyal
2020-12-22 16:19   ` Matthew Wilcox
2020-12-22 16:25     ` Vivek Goyal
2020-12-23 12:44       ` Jeff Layton
2020-12-23 12:48   ` Jeff Layton
2021-01-04 19:41     ` Vivek Goyal
2020-12-21 19:50 ` [PATCH 3/3] overlayfs: Report writeback errors on upper Vivek Goyal
2020-12-22 16:20   ` Matthew Wilcox
2020-12-22 16:29     ` Vivek Goyal
2020-12-22 17:46       ` Matthew Wilcox
2020-12-22 17:55         ` Vivek Goyal
2020-12-23 12:53           ` Jeff Layton
2020-12-23 18:20   ` Sargun Dhillon
2020-12-23 18:50     ` Matthew Wilcox
2020-12-23 19:29       ` Sargun Dhillon
2020-12-23 20:07         ` Matthew Wilcox
2020-12-23 20:21           ` Sargun Dhillon
2020-12-23 20:44             ` Matthew Wilcox
2020-12-24  9:32               ` Amir Goldstein
2020-12-24 10:12                 ` Sargun Dhillon
2020-12-24 12:13                 ` Matthew Wilcox
2020-12-25  6:50                   ` Amir Goldstein
2020-12-28 13:25                     ` Jeff Layton
2020-12-28 15:51                       ` Amir Goldstein
2021-01-04 15:51                         ` Vivek Goyal
2020-12-28 15:56                       ` Matthew Wilcox [this message]
2020-12-28 17:26                         ` Jeff Layton
2020-12-28 19:25                           ` Sargun Dhillon
2020-12-28 19:37                           ` Amir Goldstein
2020-12-28 20:48                             ` Matthew Wilcox
2021-01-02 13:25                               ` Jeff Layton
2021-01-04 16:59                         ` Vivek Goyal
2021-01-04 15:14                 ` Vivek Goyal
2021-01-04 15:22                   ` Amir Goldstein
2021-01-04 15:40                     ` Vivek Goyal
2021-01-04 21:42                       ` Amir Goldstein
2021-01-04 22:44                         ` Vivek Goyal
2021-01-05  7:11                           ` Amir Goldstein
2021-01-05 16:26                             ` Vivek Goyal
2021-01-05 16:57                               ` Amir Goldstein
2020-12-23 19:00     ` Jeff Layton
2021-01-04 20:00     ` Vivek Goyal

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