From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx153.postini.com [74.125.245.153]) by kanga.kvack.org (Postfix) with SMTP id AF46A6B005A for ; Tue, 8 Jan 2013 20:11:26 -0500 (EST) Date: Wed, 9 Jan 2013 09:12:08 +0800 From: Yuanhan Liu Subject: Re: [PATCH] mm: remove redundant var retval in sys_brk Message-ID: <20130109011208.GB304@yliu-dev.sh.intel.com> References: <1357352864-29258-1-git-send-email-yuanhan.liu@linux.intel.com> <20130108132540.e69c40f9.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130108132540.e69c40f9.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm@kvack.org On Tue, Jan 08, 2013 at 01:25:40PM -0800, Andrew Morton wrote: > On Sat, 5 Jan 2013 10:27:44 +0800 > Yuanhan Liu wrote: > > > There is only one possible return value of sys_brk, which is mm->brk no > > matter succeed or not. > > > > Cc: Andrew Morton > > Signed-off-by: Yuanhan Liu > > --- > > mm/mmap.c | 5 ++--- > > 1 files changed, 2 insertions(+), 3 deletions(-) > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > index f54b235..ae4093c 100644 > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -251,7 +251,7 @@ static unsigned long do_brk(unsigned long addr, unsigned long len); > > > > SYSCALL_DEFINE1(brk, unsigned long, brk) > > { > > - unsigned long rlim, retval; > > + unsigned long rlim; > > unsigned long newbrk, oldbrk; > > struct mm_struct *mm = current->mm; > > unsigned long min_brk; > > @@ -307,9 +307,8 @@ SYSCALL_DEFINE1(brk, unsigned long, brk) > > set_brk: > > mm->brk = brk; > > out: > > - retval = mm->brk; > > up_write(&mm->mmap_sem); > > - return retval; > > + return mm->brk; > > } > > Moving the read outside the locked region opens the possibility that > this thread will pick up the results of modification by some other > thread. > > Of course, if two threads are modifying brk at the same time then > that's a userspace problem which can still cuase inconsistent return > values, but I'm inclined to leave the code as-is just from a > quality-of-implementation POV: sys_brk() will reliably return the value > which *this thread* set. Yes. Thanks for the explanation! --yliu > > The brk() syscall returns 0 on success, so I assume glibc is throwing > this value away anyway... -- 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