linux-kernel - Re: [PATCH 07/18] mm, proc: make clear

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Date:	Mon, 29 Feb 2016 18:53:39 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Alex Deucher <alexander.deucher@....com>,
	Alex Thorlton <athorlton@....com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Christian König <christian.koenig@....com>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>,
	Davidlohr Bueso <dave@...olabs.net>,
	David Rientjes <rientjes@...gle.com>,
	"H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	linux-arch@...r.kernel.org, Mel Gorman <mgorman@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Petr Cermak <petrcermak@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 07/18] mm, proc: make clear_refs killable

On Mon 29-02-16 18:38:45, Oleg Nesterov wrote:
> On 02/29, Michal Hocko wrote:
> >
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -1027,11 +1027,15 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
> >  		};
> >
> >  		if (type == CLEAR_REFS_MM_HIWATER_RSS) {
> > +			if (down_write_killable(&mm->mmap_sem)) {
> > +				put_task_struct(task);
> > +				return -EINTR;
> > +			}
> > +
> >  			/*
> >  			 * Writing 5 to /proc/pid/clear_refs resets the peak
> >  			 * resident set size to this mm's current rss value.
> >  			 */
> > -			down_write(&mm->mmap_sem);
> >  			reset_mm_hiwater_rss(mm);
> >  			up_write(&mm->mmap_sem);
> >  			goto out_mm;
> > @@ -1043,7 +1047,10 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
> >  				if (!(vma->vm_flags & VM_SOFTDIRTY))
> >  					continue;
> >  				up_read(&mm->mmap_sem);
> > -				down_write(&mm->mmap_sem);
> > +				if (down_write_killable(&mm->mmap_sem)) {
> > +					put_task_struct(task);
> > +					return -EINTR;
> > +				}
> 
> Both lack mmput() afaics. Don't you need "goto out_mm" rather then "return" ?

Of course I need! Thanks for catching that.

> In this case you do not need put_task_struct().

Why not? Both are after get_proc_task which takes a reference to the
task...

I will send an updated patch. Thanks!

-- 
Michal Hocko
SUSE Labs