linux-kernel - Re: [PATCH, RFC] shmat: introduce flag SHM_MAP

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Date:	Tue, 7 Oct 2008 09:57:03 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH, RFC] shmat: introduce flag SHM_MAP_HINT

On Mon, Oct 06, 2008 at 09:29:23PM +0200, Andi Kleen wrote:
> On Mon, Oct 06, 2008 at 05:37:59PM +0300, Kirill A. Shutemov wrote:
> > It allows interpret attach address as a hint, not as exact address.
> 
> First you should also do a patch for the manpage and send to 
> the manpage maintainer.

I'll do it if the patch is ok.

> >  #define SHM_LOCK 	11
> > diff --git a/ipc/shm.c b/ipc/shm.c
> > index e77ec69..19462bb 100644
> > --- a/ipc/shm.c
> > +++ b/ipc/shm.c
> > @@ -819,7 +819,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
> >  	if (shmid < 0)
> >  		goto out;
> >  	else if ((addr = (ulong)shmaddr)) {
> > -		if (addr & (SHMLBA-1)) {
> > +		if (!(shmflg & SHM_MAP_HINT) && (addr & (SHMLBA-1))) {
> >  			if (shmflg & SHM_RND)
> >  				addr &= ~(SHMLBA-1);	   /* round down */
> >  			else
> > @@ -828,7 +828,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
> >  #endif
> >  					goto out;
> >  		}
> > -		flags = MAP_SHARED | MAP_FIXED;
> > +		flags = (shmflg & SHM_MAP_HINT ? 0 : MAP_FIXED) | MAP_SHARED;
> 
> 
> IMHO you need at least make the
> 
>    if (find_vma_intersection(current->mm, addr, addr + size))
>                         goto invalid;
> 
> test above conditional too.

Since it's a hint, we shouldn't call find_vma_intersection() at all.

I'll send fixed patch soon.

-- 
Regards,  Kirill A. Shutemov
 + Belarus, Minsk
 + ALT Linux Team, http://www.altlinux.com/

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