linux-kernel - Re: [PATCH net] bpf, perf: delay release of BPF prog after grace period

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Message-Id: <20160629.054333.288595753337307108.davem@davemloft.net>
Date:	Wed, 29 Jun 2016 05:43:33 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	daniel@...earbox.net
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	alexei.starovoitov@...il.com, jann@...jh.net
Subject: Re: [PATCH net] bpf, perf: delay release of BPF prog after grace
 period

From: Daniel Borkmann <daniel@...earbox.net>
Date: Mon, 27 Jun 2016 21:38:11 +0200

> Commit dead9f29ddcc ("perf: Fix race in BPF program unregister") moved
> destruction of BPF program from free_event_rcu() callback to __free_event(),
> which is problematic if used with tail calls: if prog A is attached as
> trace event directly, but at the same time present in a tail call map used
> by another trace event program elsewhere, then we need to delay destruction
> via RCU grace period since it can still be in use by the program doing the
> tail call (the prog first needs to be dropped from the tail call map, then
> trace event with prog A attached destroyed, so we get immediate destruction).
> 
> Fixes: dead9f29ddcc ("perf: Fix race in BPF program unregister")
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Acked-by: Alexei Starovoitov <ast@...nel.org>
> Cc: Jann Horn <jann@...jh.net>

Applied and queued up for -stable, thanks Daniel.