linux-kernel - Re: [PATCH] tmpfs: Disallow CONFIG_TMPFS

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Message-ID: <YB3laM3HQUM7u/Wo@chrisdown.name>
Date:   Sat, 6 Feb 2021 00:40:08 +0000
From:   Chris Down <chris@...isdown.name>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Seth Forshee <seth.forshee@...onical.com>,
        Hugh Dickins <hughd@...gle.com>,
        Amir Goldstein <amir73il@...il.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-mm@...ck.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tmpfs: Disallow CONFIG_TMPFS_INODE64 on s390

Andrew Morton writes:
>Currently there is an assumption in tmpfs that 64-bit architectures also
>have a 64-bit ino_t.  This is not true on s390 which 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.
>
>
>So prevent CONFIG_TMPFS_INODE64 from being selected on s390.
>
>Link: https://lkml.kernel.org/r/20210205230620.518245-1-seth.forshee@canonical.com
>Fixes: ea3271f7196c ("tmpfs: support 64-bit inums per-sb")
>Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
>Cc: Chris Down <chris@...isdown.name>
>Cc: Hugh Dickins <hughd@...gle.com>
>Cc: Amir Goldstein <amir73il@...il.com>
>Cc: Heiko Carstens <hca@...ux.ibm.com>
>Cc: Vasily Gorbik <gor@...ux.ibm.com>
>Cc: Christian Borntraeger <borntraeger@...ibm.com>
>Cc: <stable@...r.kernel.org>	[5.9+]
>Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

Either of the two ways presented looks fine to me, no real preference. Thanks!

Acked-by: Chris Down <chris@...isdown.name>

>---
>
> fs/Kconfig |    2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>--- a/fs/Kconfig~tmpfs-disallow-config_tmpfs_inode64-on-s390
>+++ a/fs/Kconfig
>@@ -203,7 +203,7 @@ config TMPFS_XATTR
>
> config TMPFS_INODE64
> 	bool "Use 64-bit ino_t by default in tmpfs"
>-	depends on TMPFS && 64BIT
>+	depends on TMPFS && 64BIT && !S390
> 	default n
> 	help
> 	  tmpfs has historically used only inode numbers as wide as an unsigned
>_
>