Re: [PATCH] mm, vmstat: Make sure mutex is a global static

From: Michal Hocko <mhocko@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Ying Huang <ying.huang@intel.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm, vmstat: Make sure mutex is a global static
Date: Thu, 9 Nov 2017 08:50:16 +0100	[thread overview]
Message-ID: <20171109075016.ufgjvegqghjus3wc@dhcp22.suse.cz> (raw)
In-Reply-To: <CAGXu5jKiGLAcL4QG2BoAms+JaHH-4piVe--YF3X9RhXZN53Z8Q@mail.gmail.com>

On Wed 08-11-17 07:21:20, Kees Cook wrote:
> On Tue, Nov 7, 2017 at 11:43 PM, Vlastimil Babka <vbabka@suse.cz> wrote:
> > On 11/07/2017 10:38 PM, Kees Cook wrote:
[...]
> >> +static DEFINE_MUTEX(vm_numa_stat_lock);
> >> +
> >>  int sysctl_vm_numa_stat_handler(struct ctl_table *table, int write,
> >>               void __user *buffer, size_t *length, loff_t *ppos)
> >>  {
> >>       int ret, oldval;
> >> -     DEFINE_MUTEX(vm_numa_stat_lock);
> >
> > Yeah it was Michal who suggested scoping the mutex here instead of
> > global scope, but I think he didn't mean to remove the 'static'
> > qualifier, and we both missed that in the review :(
> > So the scope under sysctl_vm_numa_stat_handler() should be okay, just
> > with the 'static' added.
> 
> That part is a matter of taste, I guess. :) But yes, static is important.

The primary reason I prefer function scope lock is that it is less
tempting to reuse the lock for something else that way. But this is
hardly something to insist on. So I am ok with the file scope as well.
-- 
Michal Hocko
SUSE Labs