linux-kernel - Re: [PATCH] bpf: fix a race between perf_event

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Message-ID: <555617C8.1070309@plumgrid.com>
Date:	Fri, 15 May 2015 08:59:04 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Wang Nan <wangnan0@...wei.com>
CC:	lizefan@...wei.com, linux-kernel@...r.kernel.org, pi3orama@....com
Subject: Re: [PATCH] bpf: fix a race between perf_event_fd and kprobe freeing

On 5/15/15 3:52 AM, Wang Nan wrote:
> According to Alexei Starovoitov (http://lkml.org/lkml/2015/5/15/29),
> there is racing between perf_event_fd and kprobe freeing:

...

> And he suggest to call perf_event_free_bpf_prog() from __free_event()
> instead of free_event_rcu() will fix the race,
...

> @@ -3564,6 +3563,8 @@ static void __free_event(struct perf_event *event)
>   		module_put(event->pmu->module);
>   	}
>
> +	perf_event_free_bpf_prog(event);
> +
>   	call_rcu(&event->rcu_head, free_event_rcu);
>   }

I don't think that's the right place. It needs to be before destroy().
I will send a patch soon.

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