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References: <20220318064959.3298768-1-davidgow@google.com>
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From:   Brendan Higgins <brendanhiggins@google.com>
Date:   Wed, 23 Mar 2022 19:56:26 -0400
Message-ID: <CAFd5g45V6P9ATGQ3kqkuFLNDB=_01gws8Ldr1kH3j+r0aSZ-Og@mail.gmail.com>
Subject: Re: [PATCH] kunit: Make kunit_remove_resource() idempotent
To:     David Gow <davidgow@google.com>
Cc:     Daniel Latypov <dlatypov@google.com>,
        Shuah Khan <skhan@linuxfoundation.org>,
        kunit-dev@googlegroups.com, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Fri, Mar 18, 2022 at 2:50 AM David Gow <davidgow@google.com> wrote:
>
> The kunit_remove_resource() function is used to unlink a resource from
> the list of resources in the test, making it no longer show up in
> kunit_find_resource().
>
> However, this could lead to a race condition if two threads called
> kunit_remove_resource() on the same resource at the same time: the
> resource would be removed from the list twice (causing a crash at the
> second list_del()), and the refcount for the resource would be
> decremented twice (instead of once, for the reference held by the
> resource list).
>
> Fix both problems, the first by using list_del_init(), and the second by
> checking if the resource has already been removed using list_empty(),
> and only decrementing its refcount if it has not.
>
> Also add a KUnit test for the kunit_remove_resource() function which
> tests this behaviour.
>
> Reported-by: Daniel Latypov <dlatypov@google.com>
> Signed-off-by: David Gow <davidgow@google.com>

Reviewed-by: Brendan Higgins <brendanhiggins@google.com>