Date: Wed, 14 Dec 2016 17:08:58 +0100
From: Petr Mladek <pmladek@suse.com>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: shuah@kernel.org, jeyu@redhat.com, rusty@rustcorp.com.au,
        ebiederm@xmission.com, dmitry.torokhov@gmail.com, acme@redhat.com,
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        rwright@hpe.com, jeffm@suse.com, DSterba@suse.com, fdmanana@suse.com,
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        subashab@codeaurora.org, xypron.glpk@gmx.de, keescook@chromium.org,
        atomlin@redhat.com, mbenes@suse.cz, paulmck@linux.vnet.ibm.com,
        dan.j.williams@intel.com, jpoimboe@redhat.com, davem@davemloft.net,
        mingo@redhat.com, akpm@linux-foundation.org,
        torvalds@linux-foundation.org, linux-kselftest@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC 06/10] kmod: provide sanity check on kmod_concurrent access
Message-ID: <20161214160858.GI16064@pathway.suse.cz>
References: <20161208184801.1689-1-mcgrof@kernel.org>
 <20161208194850.2627-1-mcgrof@kernel.org>
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On Thu 2016-12-08 11:48:50, Luis R. Rodriguez wrote:
> Only decrement *iff* we're possitive. Warn if we've hit
> a situation where the counter is already 0 after we're done
> with a modprobe call, this would tell us we have an unaccounted
> counter access -- this in theory should not be possible as
> only one routine controls the counter, however preemption is
> one case that could trigger this situation. Avoid that situation
> by disabling preemptiong while we access the counter.

I am curious about it. How could enabled preemption cause that
the counter will get negative?

Unaccounted access would be possible if put() is called
without get() or if put() is called before get().

I do not see a way how the value might get negative when
the calls are paired and ordered.

Best Regards,
Petr