linux-kernel - Re: [PATCH] tmpfs: Don't use 64-bit inodes by defulat with 32-bit ino

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Date:   Fri, 5 Feb 2021 14:55:43 -0600
From:   Seth Forshee <seth.forshee@...onical.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Hugh Dickins <hughd@...gle.com>, Chris Down <chris@...isdown.name>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tmpfs: Don't use 64-bit inodes by defulat with 32-bit
 ino_t

On Fri, Feb 05, 2021 at 12:41:57PM -0800, Andrew Morton wrote:
> On Fri,  5 Feb 2021 14:21:59 -0600 Seth Forshee <seth.forshee@...onical.com> wrote:
> 
> > Currently there seems to be an assumption in tmpfs that 64-bit
> > architectures also have a 64-bit ino_t. This is not true; s390 at
> > least has a 32-bit ino_t. With CONFIG_TMPFS_INODE64=y tmpfs
> > mounts will get 64-bit inode numbers and display "inode64" in the
> > mount options, but passing the "inode64" mount option will fail.
> > This leads to the following behavior:
> > 
> >  # mkdir mnt
> >  # mount -t tmpfs nodev mnt
> >  # mount -o remount,rw mnt
> >  mount: /home/ubuntu/mnt: mount point not mounted or bad option.
> > 
> > As mount sees "inode64" in the mount options and thus passes it
> > in the options for the remount.
> > 
> > Ideally CONFIG_TMPFS_INODE64 would depend on sizeof(ino_t) < 8,
> > but I don't think it's possible to test for this (potentially
> > CONFIG_ARCH_HAS_64BIT_INO_T or similar could be added, but I'm
> > not sure whether or not that is wanted). So fix this by simply
> > refusing to honor the CONFIG_TMPFS_INODE64 setting when
> > sizeof(ino_t) < 8.
> 
> How about changing s390 Kconfig so that CONFIG_TMPFS_INODE64 is not enabled?

I did do that for our config. I see the s390 defconfig has it enabled,
so I will send a patch for that too. But the fact that it can be
configured that way and that the code behaves badly still seems
problematic.

> 
> > Fixes: ea3271f7196c ("tmpfs: support 64-bit inums per-sb")
> > Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
> 
> With a cc:stable, I assume?

Yes, I forgot that. Thanks.

Seth