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Date: Mon, 29 Feb 2016 18:53:39 +0100
From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 07/18] mm, proc: make clear_refs killable
Message-ID: <20160229175338.GM16930@dhcp22.suse.cz>
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To: Oleg Nesterov <oleg@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, Alex Deucher <alexander.deucher@amd.com>, Alex Thorlton <athorlton@sgi.com>, Andrea Arcangeli <aarcange@redhat.com>, Andy Lutomirski <luto@amacapital.net>, Benjamin LaHaise <bcrl@kvack.org>, Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>, Daniel Vetter <daniel.vetter@intel.com>, Dave Hansen <dave.hansen@linux.intel.com>, David Airlie <airlied@linux.ie>, Davidlohr Bueso <dave@stgolabs.net>, David Rientjes <rientjes@google.com>, "H . Peter Anvin" <hpa@zytor.com>, Hugh Dickins <hughd@google.com>, Ingo Molnar <mingo@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Konstantin Khlebnikov <koct9i@gmail.com>, linux-arch@vger.kernel.org, Mel Gorman <mgorman@suse.de>, Peter Zijlstra <peterz@infradead.org>, Petr Cermak <petrcermak@chromium.org>, Thomas Gleixner <tglx@linutronix.de>

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

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