linux-kernel - Re: [PATCH v4 06/19] irqdomain: Drop revmap mutex

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Message-ID: <87zg9rx7o1.ffs@tglx>
Date:   Mon, 06 Feb 2023 14:09:02 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Johan Hovold <johan@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Marc Zyngier <maz@...nel.org>, x86@...nel.org,
        platform-driver-x86@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hsin-Yi Wang <hsinyi@...omium.org>,
        Mark-PK Tsai <mark-pk.tsai@...iatek.com>
Subject: Re: [PATCH v4 06/19] irqdomain: Drop revmap mutex

On Wed, Jan 18 2023 at 14:10, Johan Hovold wrote:
> On Wed, Jan 18, 2023 at 02:05:29PM +0100, Thomas Gleixner wrote:
>> You can do this in a two step approach.
>> 
>>     1) Add the new locking and ensure that the lock is held when
>>        the functions are called
>
> But the new locking has nothing to do with these functions. They are
> added because they fix various races elsewhere. Adding lockdep
> assertions in unrelated function as part of those fixes doesn't really
> make much sense.

Seriously? The point is that revmap_mutex is not protecting against any
of the races which you are trying to protect against. Ergo, any callsite
which does not hold the irqdomain mutex is part of the problem you are
trying to solve, no?

The removal of the revmap_mutex becomes possible due to the overall
protection scheme rework _after_ you established that all callers hold
the irqdomain mutex.

Thanks,

        tglx