netdev - Re: [PATCH bpf v2] libbpf : make libbpf_num_possible

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Message-ID: <CAADnVQLJ0LqH-ozZ2UeY=nqTR-3-96qKkt7zL1fOg2FHh-bY8A@mail.gmail.com>
Date:   Wed, 31 Jul 2019 20:40:29 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Takshak Chahande <ctakshak@...com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrey Ignatov <rdna@...com>, Kernel Team <kernel-team@...com>,
        hechaol@...com, Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: Re: [PATCH bpf v2] libbpf : make libbpf_num_possible_cpus function
 thread safe

On Wed, Jul 31, 2019 at 3:11 PM Takshak Chahande <ctakshak@...com> wrote:
>
> Having static variable `cpus` in libbpf_num_possible_cpus function
> without guarding it with mutex makes this function thread-unsafe.
>
> If multiple threads accessing this function, in the current form; it
> leads to incrementing the static variable value `cpus` in the multiple
> of total available CPUs.
>
> Used local stack variable to calculate the number of possible CPUs and
> then updated the static variable using WRITE_ONCE().
>
> Changes since v1:
>  * added stack variable to calculate cpus
>  * serialized static variable update using WRITE_ONCE()
>  * fixed Fixes tag
>
> Fixes: 6446b3155521 ("bpf: add a new API libbpf_num_possible_cpus()")
> Signed-off-by: Takshak Chahande <ctakshak@...com>

Applied. Thanks.
Thanks for keeping 'changes since v1 part' as part of git history.