linux-kernel - Re: [PATCH] ipc: Limit sysctl value to IPCMNI

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Date:   Tue, 12 Jun 2018 08:31:09 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Waiman Long <longman@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Davidlohr Bueso <dbueso@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipc: Limit sysctl value to IPCMNI

On Mon, 11 Jun 2018 23:27:08 +0200,
Waiman Long wrote:
> 
> On 06/08/2018 05:16 PM, Andrew Morton wrote:
> > On Fri,  8 Jun 2018 15:49:49 +0200 Takashi Iwai <tiwai@...e.de> wrote:
> >
> >> Currently shmmni proc entry accepts all entered integer values, but
> >> the practical limit is IPCMNI (32768).  This confuses user as if a
> >> bigger value were accepted but not applied correctly.
> >>
> >> This patch changes the proc entry to use *_minmax variant to limit the
> >> accepted values accordingly.
> > Waiman Long was working on a (vastly more complicated) patchset to
> > address this.
> >
> >> --- a/ipc/ipc_sysctl.c
> >> +++ b/ipc/ipc_sysctl.c
> >> @@ -99,6 +99,7 @@ static int proc_ipc_auto_msgmni(struct ctl_table *table, int write,
> >>  static int zero;
> >>  static int one = 1;
> >>  static int int_max = INT_MAX;
> >> +static int ipcmni = IPCMNI;
> >>  
> >>  static struct ctl_table ipc_kern_table[] = {
> >>  	{
> >> @@ -120,7 +121,9 @@ static struct ctl_table ipc_kern_table[] = {
> >>  		.data		= &init_ipc_ns.shm_ctlmni,
> >>  		.maxlen		= sizeof(init_ipc_ns.shm_ctlmni),
> >>  		.mode		= 0644,
> >> -		.proc_handler	= proc_ipc_dointvec,
> >> +		.proc_handler	= proc_ipc_dointvec_minmax,
> >> +		.extra1		= &zero,
> >> +		.extra2		= &ipcmni,
> >>  	},
> >>  	{
> >>  		.procname	= "shm_rmid_forced",
> > What is the back-compatibility situation here?
> >
> >
> Sorry for the late reply. I am planning to send out an updated patch
> once the merge window is closed. The latest patch can be found in
> 
> https://lkml.org/lkml/2018/5/7/666
> 
> Luis has some concern about the use of __read_mostly tag which I am
> going to remove in the next version.

Thanks, that's as trivial as my patch, unsurprisingly :)


Takashi