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From: Thomas Gleixner <tglx@linutronix.de>
To: Davidlohr Bueso <dbueso@suse.de>
Cc: Mel Gorman <mgorman@techsingularity.net>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Chris Mason <clm@fb.com>, Darren Hart <dvhart@linux.intel.com>,
	dave@stgolabs.net, linux-kernel@vger.kernel.org,
	Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH v4] futex: Remove requirement for lock_page in get_futex_key
Date: Wed, 27 Jan 2016 21:10:02 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.11.1601272105060.3886@nanos> (raw)
In-Reply-To: <1453569254-25928-1-git-send-email-dbueso@suse.de>

On Sat, 23 Jan 2016, Davidlohr Bueso wrote:
> +	if (unlikely(!mapping)) {
> +		int shmem_swizzled;
> +
> +		/*
> +		 * Page lock is required to identify which special case above
> +		 * applies. If this is really a shmem page then the page lock
> +		 * will prevent unexpected transitions.
> +		 */
> +		lock_page(page);
> +		shmem_swizzled = PageSwapCache(page);
>  		unlock_page(page);
>  		put_page(page);
> +		WARN_ON_ONCE(READ_ONCE(page->mapping));

You just did put_page(page). So dereferencing page is a nono. This needs to be
flipped around.

Thanks,

	tglx

  reply	other threads:[~2016-01-27 20:11 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-23 17:14 Davidlohr Bueso
2016-01-27 20:10 ` Thomas Gleixner [this message]
2016-01-28  3:02 ` Hugh Dickins
2016-01-29 18:35   ` Davidlohr Bueso
2016-01-29 18:46     ` Hugh Dickins

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