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From: Dave Chinner <>
To: Amir Goldstein <>
Cc: "Darrick J . Wong" <>,
	Eryu Guan <>,
	Miklos Szeredi <>,,
Subject: Re: [PATCH] xfs: fix GPF in swapfile_activate of file from overlayfs
Date: Sat, 25 Aug 2018 09:39:01 +1000	[thread overview]
Message-ID: <20180824233901.GA2234@dastard> (raw)
In-Reply-To: <>

On Fri, Aug 24, 2018 at 12:02:51PM +0300, Amir Goldstein wrote:
> Since overlayfs implements stacked file operations, f_inode
> is no longer euqivalent to f_mapping->host and xfs should use
> the latter, same as generic_swapfile_activate().

Since when has file_inode() not pointed to the inode backing the
struct file?

> Using f_inode results in an attempt to dereference an xfs_inode
> struct from an ovl_inode pointer:
>  CPU: 0 PID: 2462 Comm: swapon Not tainted
>  4.18.0-xfstests-12721-g33e17876ea4e #3402
>  RIP: 0010:xfs_find_bdev_for_inode+0x23/0x2f
>  Call Trace:
>   xfs_iomap_swapfile_activate+0x1f/0x43
>   __se_sys_swapon+0xb1a/0xee9
> Fixes: d1d04ef8572b ("ovl: stack file ops")

Oh, since about 3 days ago.

So now we've got to deal with a vfs interface change that isn't
documented, hasn't been clearly communicated prior to merging, and
it subtly breaks a subset of callers.

So, please enlighten me with a documentation patch before changing
any XFS code: What is the new behaviour and the rules we must follow
for calling file_inode()?

I'm also interested in understanding whether anyone auditted all the
callers to see if they follow those rules.  There are another
20-odd file_inode() calls in XFS, and ~750 across fs/. How many
other places have been checked for correctness under the new rules?

i.e.  I can't review this patch without also confirming that all the
other file_inode() callers in XFS are still correct, and I can't do
that until I understand what the new behaviour of file_inode() is
and when it is not safe to use.


Dave Chinner

  reply	other threads:[~2018-08-25  3:15 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-24  9:02 [PATCH] xfs: fix GPF in swapfile_activate of file from overlayfs Amir Goldstein
2018-08-24 23:39 ` Dave Chinner [this message]
2018-08-25 10:47   ` Amir Goldstein
2018-08-25 20:04     ` Miklos Szeredi
2018-08-26 11:32       ` Amir Goldstein
2018-08-26 22:59         ` Dave Chinner
2018-08-27  7:17           ` Amir Goldstein
2018-08-26 22:52     ` Dave Chinner

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