linux-kernel - Re: [PATCH] fat: Fix sb

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Message-Id: <20171128144127.e4903df58c8c3e7c783dd61b@linux-foundation.org>
Date:   Tue, 28 Nov 2017 14:41:27 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Joe Perches <joe@...ches.com>
Cc:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        David Howells <dhowells@...hat.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fat: Fix sb_rdonly() change

On Thu, 23 Nov 2017 22:51:34 -0800 Joe Perches <joe@...ches.com> wrote:

> On Fri, 2017-11-24 at 15:07 +0900, OGAWA Hirofumi wrote:
> > Joe Perches <joe@...ches.com> writes:
> > 
> > > On Thu, 2017-11-23 at 15:29 +0900, OGAWA Hirofumi wrote:
> > > > Ouch forgot to add stable@
> > > > 
> > > > -- 
> > > > commit bc98a42c1f7d0f886c0c1b75a92a004976a46d9f introduced bug.
> > > 
> > > I think your commit message needs a bit more information.
> > > 
> > > It'd be useful to describe that the introduction of
> > > sb_rdonly converted the bitwise & to a boolean and so
> > > this conversion and comparison was made defective.
> > > 
> > > Are there any other instances of defective comparisons?
> > 
> > Please ask to that patch author.
> 
> The patch author, David Howells, is on the cc list.
> 
> btw:
> 
> It seems all the the other uses use a (bool) cast of the
> (*flags & MS_RDONLY) and a comparison of sb_rdonly(sb).

Sentence is hard to understand.

> It would make sense to change the argument type of the
> ext[24]_setup_super int read_only arg to bool to match
> the sb_rdonly() type. 

I did this:

: From: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
: Subject: fat: Fix sb_rdonly() change
: 
: bc98a42c1f7d0f ("VFS: Convert sb->s_flags & MS_RDONLY to sb_rdonly(sb)")
: converted fat_remount():new_rdonly from a bool to an int.  However
: fat_remount() depends upon the compiler's conversion of a non-zero integer
: into boolean `true'.
: 
: Fix it by switching `new_rdonly' back into a bool.
: 
: Link: http://lkml.kernel.org/r/87mv3d5x51.fsf@mail.parknet.co.jp
: Fixes: bc98a42c1f7d0f8 ("VFS: Convert sb->s_flags & MS_RDONLY to sb_rdonly(sb)")
: Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
: Cc: Joe Perches <joe@...ches.com>
: Cc: David Howells <dhowells@...hat.com>
: Cc: <stable@...r.kernel.org>
: Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
: ---
: 
:  fs/fat/inode.c |    2 +-
:  1 file changed, 1 insertion(+), 1 deletion(-)
: 
: diff -puN fs/fat/inode.c~fat-fix-sb_rdonly-change fs/fat/inode.c
: --- a/fs/fat/inode.c~fat-fix-sb_rdonly-change
: +++ a/fs/fat/inode.c
: @@ -779,7 +779,7 @@ static void __exit fat_destroy_inodecach
:  
:  static int fat_remount(struct super_block *sb, int *flags, char *data)
:  {
: -	int new_rdonly;
: +	bool new_rdonly;
:  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
:  	*flags |= SB_NODIRATIME | (sbi->options.isvfat ? 0 : SB_NOATIME);
:  
: _