linux-kernel - Re: [PATCH] mqueue: sys_mq_open: do not call mnt_drop

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Date:	Tue, 19 Mar 2013 14:09:40 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>, <linux-kernel@...r.kernel.org>,
	<devel@...nvz.org>, Doug Ledford <dledford@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] mqueue: sys_mq_open: do not call mnt_drop_write() if
 read-only

On Tue, 19 Mar 2013 13:31:18 +0400 Vladimir Davydov <vdavydov@...allels.com> wrote:

> mnt_drop_write() must be called only if mnt_want_write() succeeded,
> otherwise the mnt_writers counter will diverge.
> 
> ...
>
> --- a/ipc/mqueue.c
> +++ b/ipc/mqueue.c
> @@ -840,7 +840,8 @@ out_putfd:
>  		fd = error;
>  	}
>  	mutex_unlock(&root->d_inode->i_mutex);
> -	mnt_drop_write(mnt);
> +	if (!ro)
> +		mnt_drop_write(mnt);
>  out_putname:
>  	putname(name);
>  	return fd;

huh, that's been there for a while.  What were the runtime-visible
effects of the bug?
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