From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8B55546AA68 for ; Tue, 21 Jul 2026 15:32:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784647936; cv=none; b=Vz9fYYHsWLBvpM/CR4MT3KTPVBCUyYKEbtz1EdDFJ7t0vHyIKEoPrakeIuI9Mbb/re14NpM5lU/G6jda+3pl+du15fQ/PLku3To1WZy/iVckYCXWh7HuJfT5orFhPEVnKFNRptXn3ZlqHKhRXi+Zx7o4Bcl70bIJEtPloT245cg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784647936; c=relaxed/simple; bh=FAouj4DJQsSL177U3PztIpS40g6ZLZq07pNm2m8o5iY=; h=Message-ID:Date:MIME-Version:Subject:To:References:From:Cc: In-Reply-To:Content-Type; b=KTdXqddnAqGSXoWvatYd8w8x6WJ1EI0S3tFqmPYiGb8Yc0IDicDsaVx7luYxPIoVDJSRlLwXgyiiHKyV0CrNjTX/8+bXZUAzF3n768qcqEnUkKLYeDS+Wy6bFlwG3D5wFFoJNDzjXUlInhjd2GSs3D9TUfVAbKPv7AYQNIM8Jsw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MahIJnGs; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MahIJnGs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA7BC1F000E9; Tue, 21 Jul 2026 15:32:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784647935; bh=WrYvLMv1hdIePlAKuyeYLDeHqVuCYr+gC4eT/4t81BI=; h=Date:Subject:To:References:From:Cc:In-Reply-To; b=MahIJnGsx/7e2GBE8+1A6AocAlprphqZYD5kqJVwv6shB87yNo4C+Xf6Q8SLozJbL 7HiUvvCDCOdJr7zkbvObTiuESxx+OnV9BzurWmnTgWJOz0BXtFFFckIjvpYstuCa4c eVMoHHtiq3MpiFObB3XIw5Xartkhe8QnHpzqWXyS5ffY4NkN1WmUwtAwaQ5B2UAGe5 5ktWSuUk00Rgugd/h3VysVjT9tjRWPTTFg5bNtepkyVJxKwAi6LS9J2z2De3Od+b9u 8VWYatLfRXJxBWUf6Zfj7tfHYd+PjYyk0jadOi8rmF/OHVjOlYI0jNOlQXqj8g3GDG fhWdjCLh5vC1w== Message-ID: <061288be-4e92-4060-a7ac-24d329f4186f@kernel.org> Date: Tue, 21 Jul 2026 17:32:12 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH mptcp-net v2] mptcp: pm: fix data race in add_addr timer callback Content-Language: fr To: luoqing References: <20260717064028.767876-1-l1138897701@163.com> From: Matthieu Baerts Cc: mptcp@lists.linux.dev Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, Thank you for sharing this patch. I have similar comments than the ones I sent on: https://lore.kernel.org/178410664361.3802972.16804879942885801851.b4-review@b4 On 17/07/2026 08:40, luoqing wrote: > From: luoqing > > The timer callback reads entry->retrans_times outside pm.lock to decide > whether to call mptcp_pm_subflow_established(). Since > mptcp_pm_announced_del_timer() can concurrently set retrans_times = > ADD_ADDR_RETRANS_MAX under pm.lock, a race condition exists. How did you find the bug? Do you have a reproducer or is it by analysing the code? Were you assisted by a tool/LLM? If yes, please add the Assisted-by tag. > Use a local 'completed' flag set inside pm.lock only when the timer > callback itself increments retrans_times to ADD_ADDR_RETRANS_MAX. This > ensures that mptcp_pm_subflow_established() is only called when the > retransmission naturally exhausts. A fix should have a Fixes tag, please add one. > Signed-off-by: luoqing For legal reasons, you are supposed to put your full name. Having only one "word" for your full name, without capital letters looks wrong, no? > diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c > index 6afd39aea110..ed39a1241ffd 100644 > --- a/net/mptcp/pm.c > +++ b/net/mptcp/pm.c > @@ -380,6 +380,8 @@ static void mptcp_pm_add_addr_timer(struct timer_list *timer) > struct mptcp_sock *msk = entry->sock; > struct sock *sk = (struct sock *)msk; > unsigned int timeout = 0; > + bool completed = false; > + u8 retrans_times; Do you need two new variables? One should be enough. > > pr_debug("msk=%p\n", msk); > > @@ -399,27 +401,32 @@ static void mptcp_pm_add_addr_timer(struct timer_list *timer) > > spin_lock_bh(&msk->pm.lock); > > + retrans_times = READ_ONCE(entry->retrans_times); Why do you require READ_ONCE() here? Can retrans_times be modified without the pm lock? > + > /* The cancel path (mptcp_pm_announced_del_timer()) can race with this > * callback. Once cancel updates retrans_times to MAX, suppress further > * retransmissions here. If this callback acquires pm.lock first, one > * final transmit attempt is still possible. > */ > - if (entry->retrans_times < ADD_ADDR_RETRANS_MAX && > + if (retrans_times < ADD_ADDR_RETRANS_MAX && > !mptcp_pm_should_add_signal_addr(msk)) { > pr_debug("retransmit ADD_ADDR id=%d\n", entry->addr.id); > mptcp_pm_announce_addr(msk, &entry->addr, false); > mptcp_pm_add_addr_send_ack(msk); > - entry->retrans_times++; > + retrans_times++; > + WRITE_ONCE(entry->retrans_times, retrans_times); Same here, why WRITE_ONCE()? > } > > - if (entry->retrans_times < ADD_ADDR_RETRANS_MAX) > - timeout <<= entry->retrans_times; > - else > + if (retrans_times < ADD_ADDR_RETRANS_MAX) > + timeout <<= retrans_times; > + else { > timeout = 0; > + completed = true; > + } Either you have: completed = entry->retrans_times >= ADD_ADDR_RETRANS_MAX; if (!completed) timeout <<= retrans_times; else timeout = 0; (preferred) or if (entry->retrans_times < ADD_ADDR_RETRANS_MAX) timeout <<= retrans_times; else timeout = 0; retrans_times = entry->retrans_times; But I don't think you need to have both "completed" and "retrans_times". With only "completed", you can minimise this patch. > > spin_unlock_bh(&msk->pm.lock); > > - if (entry->retrans_times == ADD_ADDR_RETRANS_MAX) > + if (completed) > mptcp_pm_subflow_established(msk); > > out: Cheers, Matt -- Sponsored by the NGI0 Core fund.