linux-kernel - Re: [PATCH v3 2/4] kmod: reduce atomic operations on kmod

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Date:   Mon, 26 Jun 2017 13:36:44 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     akpm@...ux-foundation.org, jeyu@...hat.com, shuah@...nel.org,
        rusty@...tcorp.com.au, ebiederm@...ssion.com,
        dmitry.torokhov@...il.com, acme@...hat.com, corbet@....net,
        josh@...htriplett.org, martin.wilck@...e.com, mmarek@...e.com,
        hare@...e.com, rwright@....com, jeffm@...e.com, DSterba@...e.com,
        fdmanana@...e.com, neilb@...e.com, linux@...ck-us.net,
        rgoldwyn@...e.com, subashab@...eaurora.org, xypron.glpk@....de,
        keescook@...omium.org, atomlin@...hat.com, mbenes@...e.cz,
        paulmck@...ux.vnet.ibm.com, dan.j.williams@...el.com,
        jpoimboe@...hat.com, davem@...emloft.net, mingo@...hat.com,
        alan@...ux.intel.com, tytso@....edu, gregkh@...uxfoundation.org,
        torvalds@...ux-foundation.org, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/4] kmod: reduce atomic operations on kmod_concurrent
 and simplify

On Fri 2017-05-26 14:12:26, Luis R. Rodriguez wrote:
> atomic operations. We do this by inverting the logic of of the enabler,
> instead of incrementing kmod_concurrent as we get new kmod users, define the
> variable kmod_concurrent_max as the max number of currently allowed kmod
> users and as we get new kmod users just decrement it if its still positive.
> This combines the dec and read in one atomic operation.
> 
> In this case we no longer get the same false failure:
> 
> CPU1			CPU2
> atomic_dec_if_positive()
> 			atomic_dec_if_positive()
> atomic_inc()
> 			atomic_inc()
> 
> Suggested-by: Petr Mladek <pmladek@...e.com>
> Suggested-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>

The change looks fine to me. The code is much easier and less hacky.

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr