linux-kernel - Re: [PATCH v3 5/6] ANDROID: binder: don't check prio permissions on restore.

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Message-ID: <20171115130812.2xvbxfuyfq7opa7g@hirez.programming.kicks-ass.net>
Date:   Wed, 15 Nov 2017 14:08:12 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Martijn Coenen <maco@...roid.com>
Cc:     gregkh@...uxfoundation.org, john.stultz@...aro.org,
        tkjos@...gle.com, arve@...roid.com, sherryy@...roid.com,
        tglx@...utronix.de, amit.pundir@...aro.org,
        linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
        maco@...gle.com
Subject: Re: [PATCH v3 5/6] ANDROID: binder: don't check prio permissions on
 restore.

On Thu, Oct 26, 2017 at 04:07:49PM +0200, Martijn Coenen wrote:
> Because we have disabled RT priority inheritance for
> the regular binder domain, the following can happen:
> 
> 1) thread A (prio 98) calls into thread B
> 2) because RT prio inheritance is disabled, thread B
>    runs at the lowest nice (prio 100) instead
> 3) thread B calls back into A; A will run at prio 100
>    for the duration of the transaction

That sounds wrong.. Why would you ever downgrade A?