From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (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 E53D0286427 for ; Tue, 23 Sep 2025 02:07:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758593260; cv=none; b=gC8XR7y4uylO8pL/kUZuslLQFovTxRVhOhtgT5RoZMhvnRXy/c3KufnTWsZoTpMknd1rzh2htEH0OtBd8HCtTx7sV6ZD7QLsKayUcPjSGYtOkOI3WcXFsR4n3oGoZu4ZbKSOAFGawP/sFPv76xrc+EY2cOsC4ZnHvS3pcNG/WOA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758593260; c=relaxed/simple; bh=5Wb9m62FfFTrECQZbqRXPoInZRSGH+uaxVzcuR6tqDA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cXAD3sADyWPpf0a3r791JwBoIrL5eLOb9K+hi58dQLBAQJxtkVgCQhMeq0PcfMszYIYulnyGtkIBkLYKSim6xNbLhwwJ47tFFObHiq7uOQv1LUihl4QPKFPyTnhyLGacObmGkNxLDbx2eHnWwKku2F8ZyoDRPxlhA93e+Sujiok= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=wogl13CX; arc=none smtp.client-ip=91.218.175.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="wogl13CX" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758593252; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=jPHHDyBu7fbsLMcBrmfdxFEmohUKJ5Cry6I2TtdMTBk=; b=wogl13CXH1rjboajAXBQOwoINEWo2XXVMxMc/RzM3HScEE03NeSeFyE2siP2h4DBUDqZql klYfumSOpw73HacB0e3dNm3LXSLLQqkBDYYqmAY46pYCEe1Tq0lTzO7oeHWEbQ6AiUHucp q/ibrbzYYfH+czxMqsHbot3XoJOIkiQ= Date: Tue, 23 Sep 2025 10:07:28 +0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH net-next v4 3/3] inet: Avoid ehash lookup race in inet_twsk_hashdance_schedule() To: Kuniyuki Iwashima Cc: edumazet@google.com, kerneljasonxing@gmail.com, davem@davemloft.net, kuba@kernel.org, netdev@vger.kernel.org, Xuanqiang Luo References: <20250920105945.538042-1-xuanqiang.luo@linux.dev> <20250920105945.538042-4-xuanqiang.luo@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: luoxuanqiang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 在 2025/9/23 08:45, Kuniyuki Iwashima 写道: > On Sat, Sep 20, 2025 at 4:00 AM wrote: >> From: Xuanqiang Luo >> >> Since ehash lookups are lockless, if another CPU is converting sk to tw >> concurrently, fetching the newly inserted tw with tw->tw_refcnt == 0 cause >> lookup failure. >> >> The call trace map is drawn as follows: >> CPU 0 CPU 1 >> ----- ----- >> inet_twsk_hashdance_schedule() >> spin_lock() >> inet_twsk_add_node_rcu(tw, ...) >> __inet_lookup_established() >> (find tw, failure due to tw_refcnt = 0) >> __sk_nulls_del_node_init_rcu(sk) >> refcount_set(&tw->tw_refcnt, 3) >> spin_unlock() >> >> By replacing sk with tw atomically via hlist_nulls_replace_init_rcu() after >> setting tw_refcnt, we ensure that tw is either fully initialized or not >> visible to other CPUs, eliminating the race. >> >> It's worth noting that we replace under lock_sock(), so no need to check if sk >> is hashed. Thanks to Kuniyuki Iwashima! >> >> Fixes: 3ab5aee7fe84 ("net: Convert TCP & DCCP hash tables to use RCU / hlist_nulls") >> Suggested-by: Kuniyuki Iwashima > This is not needed. A pure review does not deserve Suggested-by. > This is used when someone suggests changing the core idea of > the patch. Got it, but still really appreciate your detailed and patient review! > >> Signed-off-by: Xuanqiang Luo >> --- >> net/ipv4/inet_timewait_sock.c | 13 ++++--------- >> 1 file changed, 4 insertions(+), 9 deletions(-) >> >> diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c >> index 5b5426b8ee92..bb98888584a8 100644 >> --- a/net/ipv4/inet_timewait_sock.c >> +++ b/net/ipv4/inet_timewait_sock.c >> @@ -116,7 +116,7 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, >> spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash); >> struct inet_bind_hashbucket *bhead, *bhead2; >> >> - /* Step 1: Put TW into bind hash. Original socket stays there too. >> + /* Put TW into bind hash. Original socket stays there too. >> Note, that any socket with inet->num != 0 MUST be bound in >> binding cache, even if it is closed. >> */ >> @@ -140,14 +140,6 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, >> >> spin_lock(lock); >> >> - /* Step 2: Hash TW into tcp ehash chain */ >> - inet_twsk_add_node_rcu(tw, &ehead->chain); >> - >> - /* Step 3: Remove SK from hash chain */ >> - if (__sk_nulls_del_node_init_rcu(sk)) >> - sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); >> - >> - >> /* Ensure above writes are committed into memory before updating the >> * refcount. >> * Provides ordering vs later refcount_inc(). >> @@ -162,6 +154,9 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, >> */ >> refcount_set(&tw->tw_refcnt, 3); > I discussed this series with Eric last week, and he pointed out > (thanks!) that we need to be careful here about memory barrier. > > refcount_set() is just WRITE_ONCE() and thus can be reordered, > and twsk could be published with 0 refcnt, resulting in another RST. > Thanks for Eric's pointer! Could you let me know if my modification here works? That is, moving smp_wmb() to after the refcount update: @@ -140,19 +140,6 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, spin_lock(lock); - /* Step 2: Hash TW into tcp ehash chain */ - inet_twsk_add_node_rcu(tw, &ehead->chain); - - /* Step 3: Remove SK from hash chain */ - if (__sk_nulls_del_node_init_rcu(sk)) - sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); - - - /* Ensure above writes are committed into memory before updating the - * refcount. - * Provides ordering vs later refcount_inc(). - */ - smp_wmb(); /* tw_refcnt is set to 3 because we have : * - one reference for bhash chain. * - one reference for ehash chain. @@ -162,6 +149,14 @@ void inet_twsk_hashdance_schedule(struct inet_timewait_sock *tw, */ refcount_set(&tw->tw_refcnt, 3); + /* Ensure tw_refcnt has been set before tw is published by + * necessary memory barrier. + */ + smp_wmb(); + + hlist_nulls_replace_init_rcu(&sk->sk_nulls_node, &tw->tw_node); + sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); + inet_twsk_schedule(tw, timeo); spin_unlock(lock); Thanks! Xuanqiang >> + hlist_nulls_replace_init_rcu(&sk->sk_nulls_node, &tw->tw_node); >> + sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1); >> + >> inet_twsk_schedule(tw, timeo); >> >> spin_unlock(lock); >> -- >> 2.25.1 >>