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Date: Mon, 29 Feb 2016 18:54:18 +0100
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH 08/18] mm, fork: make dup_mmap wait for mmap_sem for
 write killable
Message-ID: <20160229175418.GD3615@redhat.com>
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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>, 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>, Michal Hocko <mhocko@suse.com>
Message-ID: <20160229175418.FMEkjtvLjgfyevtCzy8BjlbrwKRhY5ddjaFpS-I5XOc@z>

On 02/29, Michal Hocko wrote:
>
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -413,7 +413,10 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
>  	unsigned long charge;
>  
>  	uprobe_start_dup_mmap();
> -	down_write(&oldmm->mmap_sem);
> +	if (down_write_killable(&oldmm->mmap_sem)) {
> +		uprobe_end_dup_mmap();
> +		return -EINTR;
> +	}

This is really cosmetic and subjective, I won't insist if you prefer it this way.

But perhaps it makes sense to add another "fail" label above uprobe_end_dup_mmap()
we already have... IMO it is always better to avoid duplicating when it comes to
"unlock".

Oleg.