linux-kernel - Re: [PATCH] ipc,sem block sem_lock on sma->lock during sma initialization

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Date:	Fri, 21 Nov 2014 12:09:30 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Manfred Spraul <manfred@...orfullife.com>,
	Davidlohr Bueso <davidlohr@...com>,
	Rafael Aquini <aquini@...hat.com>
Subject: Re: [PATCH] ipc,sem block sem_lock on sma->lock during sma
 initialization

On Fri, 21 Nov 2014 14:52:26 -0500 Rik van Riel <riel@...hat.com> wrote:

> When manipulating just one semaphore with semop, sem_lock only takes that
> single semaphore's lock. This creates a problem during initialization of
> the semaphore array, when the data structures used by sem_lock have not
> been set up yet. The sma->lock is already held by newary, and we just
> have to make sure everything else waits on that lock during initialization.
> 
> Luckily it is easy to make sem_lock wait on the sma->lock, by pretending
> there is a complex operation in progress while the sma is being initialized.
> 
> The newary function already zeroes sma->complex_count before unlocking
> the sma->lock.

What are the runtime effects of the bug?
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