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

From: Andrew Morton
Date: Fri Nov 21 2014 - 15:09:35 EST

On Fri, 21 Nov 2014 14:52:26 -0500 Rik van Riel <riel@xxxxxxxxxx> 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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