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

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Date:   Mon, 11 Jun 2018 17:27:08 -0400
From:   Waiman Long <longman@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Takashi Iwai <tiwai@...e.de>
Cc:     Davidlohr Bueso <dbueso@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipc: Limit sysctl value to IPCMNI

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.

-Longman