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Date: Mon, 29 Feb 2016 18:38:45 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Alex Deucher <alexander.deucher@amd.com>,
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        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>,
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        Petr Cermak <petrcermak@chromium.org>,
        Thomas Gleixner <tglx@linutronix.de>, Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH 07/18] mm, proc: make clear_refs killable
Message-ID: <20160229173845.GC3615@redhat.com>
References: <1456752417-9626-1-git-send-email-mhocko@kernel.org>
 <1456752417-9626-8-git-send-email-mhocko@kernel.org>
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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" ? In
this case you do not need put_task_struct().

Oleg.