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From: Jakub Kicinski <jakub.kicinski@netronome.com>
To: Takshak Chahande <ctakshak@fb.com>
Cc: <netdev@vger.kernel.org>, <ast@kernel.org>,
	<daniel@iogearbox.net>, <rdna@fb.com>, <kernel-team@fb.com>,
	<hechaol@fb.com>
Subject: Re: [PATCH bpf-next] libbpf : make libbpf_num_possible_cpus function thread safe
Date: Tue, 30 Jul 2019 16:05:02 -0700	[thread overview]
Message-ID: <20190730160502.699d0b9a@cakuba.netronome.com> (raw)
In-Reply-To: <20190730222447.3918919-1-ctakshak@fb.com>

On Tue, 30 Jul 2019 15:24:47 -0700, Takshak Chahande 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.
> 
> Let caching the number of possile CPUs handled by libbpf's users than
> this library itself; 

Can we just use stack variable for the calculations and
READ_ONCE()/WRITE_ONCE() for assignment to the static?  
libbpf itself uses this helper so caller caching wouldn't
work there.

> and let this function be rock bottom one which reads
> and parse the file (/sys/devices/system/cpu/possible) everytime it gets
> called to simplify the things.

I don't understand can you rephrase?

> Fixes: 6446b3155521 (bpf: add a new API libbpf_num_possible_cpus())
> 

No new line after the fixes tag, also I think you're missing quotation
marks around the commit title?

> Signed-off-by: Takshak Chahande <ctakshak@fb.com>
> Acked-by: Andrey Ignatov <rdna@fb.com>

      reply	other threads:[~2019-07-30 23:05 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-30 22:24 [PATCH bpf-next] libbpf : make libbpf_num_possible_cpus function thread safe Takshak Chahande
2019-07-30 23:05 ` Jakub Kicinski [this message]

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