From mboxrd@z Thu Jan 1 00:00:00 1970 From: Manfred Spraul Subject: Re: [PATCH v3] ipc,shm: disable shmmax and shmall by default Date: Fri, 18 Apr 2014 11:26:02 +0200 Message-ID: <5350EFAA.2030607@colorfullife.com> References: <1397784345.2556.26.camel@buesod1.americas.hpqcorp.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1397784345.2556.26.camel@buesod1.americas.hpqcorp.net> Sender: owner-linux-mm@kvack.org To: Davidlohr Bueso , Andrew Morton Cc: Michael Kerrisk , KOSAKI Motohiro , Kamezawa Hiroyuki , Greg Thelen , aswin@hp.com, LKML , "linux-mm@kvack.org" , linux-api@vger.kernel.org List-Id: linux-api@vger.kernel.org Hi Davidlohr, On 04/18/2014 03:25 AM, Davidlohr Bueso wrote: > So a value of 0 bytes or pages, for shmmax and shmall, respectively, > implies unlimited memory, as opposed to disabling sysv shared memory. That might be a second risk: Right now, a sysadmin can prevent sysv memory allocations with # sysctl kernel.shmall=0 After your patch is applied, this line allows unlimited allocations. Obviously my patch has the opposite problem: 64-bit wrap-arounds. > --- a/include/uapi/linux/shm.h > +++ b/include/uapi/linux/shm.h > @@ -9,14 +9,14 @@ > > /* > * SHMMAX, SHMMNI and SHMALL are upper limits are defaults which can > - * be increased by sysctl > + * be modified by sysctl. By default, disable SHMMAX and SHMALL with > + * 0 bytes, thus allowing processes to have unlimited shared memory. > */ > - > -#define SHMMAX 0x2000000 /* max shared seg size (bytes) */ > +#define SHMMAX 0 /* max shared seg size (bytes) */ > #define SHMMIN 1 /* min shared seg size (bytes) */ > #define SHMMNI 4096 /* max num of segs system wide */ > #ifndef __KERNEL__ > -#define SHMALL (SHMMAX/getpagesize()*(SHMMNI/16)) > +#define SHMALL 0 > #endif > #define SHMSEG SHMMNI /* max shared segs per process */ > The "#ifndef __KERNEL__" is not required: As there is no reference to PAGE_SIZE anymore, one definition for SHMALL is sufficient. -- Manfred -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org