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 7849230566D; Sat, 22 Aug 2026 05:25:01 +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=1787376302; cv=none; b=ehW193+V977O4mKFE4En7+SP1rn/PDZhwKGc7EU0dx4kEt2y+jGMMyfiyKvR+xcvw1fmBX92qeIqeQUBTu5/Aa1HNTBa3qNmYOl6lpN38KqoV/YkX/4R9xAdwAkfM9u4wKFooC2BrU1nWJL3X4WE3485wyhZvIv5YzqZhwG6Zns= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787376302; c=relaxed/simple; bh=mt2Xg+eBQiPmZxAcVQtN4fGlLb/Eh6ZY/lYKS5zx+v4=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=HuuIZskSuG6UBJbdIpCOuQYJi+fBOdEJb2vspATaTRicPs8OaTZkqfBA/aIj+B8OOJ4/gGJmgVHApfFEJ5jB3J3QUbaOzk0mFoDaAYeyVujT9VE4AJCNtCXs2d3q6Psco1GAyc8ChMA9UqyAeuWVKI1AJrGDtCm+rnIPyh7zu/c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VOviTrjX; 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="VOviTrjX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D597C1F00A3D; Sat, 22 Aug 2026 05:25:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787376301; bh=WrxZXYDQSCaaLdiFxe6P5cFFZC053cuH9qY49ZMD9N0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=VOviTrjXK4KuuoGV769qBO0+BNcX4PRLs3w/wzc2uoglJlTQxu7wDBqZqxXB0gQ0C mg97H8+/gpOB0A3LydTNSruYAokBaNe8KyMF0NAUAPP4mSObso5QL4+r5HcXmEekZf Y/ao+a0oApZTxdCcAF5tok7YFfMZXUUYR9RkDDcnlShC13POiCqlxzbymhJ+zmSd+M IgBB/lIkTS/FKir7VSMEvMcvCiotH7N0sjZpDcP6Y7x3nE53JjdBRpzOTf6oW0xXkt r7fs62pFrpA3br96gOwohOMTY8vmlQyTrKbgTiQ0nlq4ZBK44h7VOIMSwQkcWSlXO2 nrut+hoxzl5LA== From: Allison Henderson To: netdev@vger.kernel.org, linux-rdma@vger.kernel.org, pabeni@redhat.com, edumazet@google.com, kuba@kernel.org, horms@kernel.org Cc: achender@kernel.org, jhubbard@nvidia.com, woni9911@gmail.com, michal.kubiak@intel.com, leon@kernel.org Subject: [PATCH net v3 1/5] net/rds: use wq_has_sleeper() in release_in_xmit() Date: Fri, 21 Aug 2026 22:24:55 -0700 Message-Id: <20260822052459.88017-2-achender@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260822052459.88017-1-achender@kernel.org> References: <20260822052459.88017-1-achender@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit release_in_xmit() clears RDS_IN_XMIT with clear_bit_unlock() and then checks waitqueue_active() to decide whether anyone needs waking. clear_bit_unlock() is only a release operation: it orders the critical section before the bit clear, but does not order the subsequent plain load of the wait queue head after it. The waiter side does the mirror image - it adds itself to the wait queue and then tests the bit. That is the classic store-buffering pattern: the releasing CPU can read the wait queue as empty while the waiting CPU still reads the bit as set, so the sleeper is never woken. The waiters are rds_conn_shutdown() and rds_tcp_reset_callbacks(), both in uninterruptible wait_event() with no timeout. A lost wake-up strands the shutdown worker on its single-threaded workqueue until some other sender releases the bit again - and on a connection that is being torn down precisely because it failed, there may never be another sender. The barrier used to be there: release_in_xmit() did clear_bit() followed by smp_mb__after_atomic() until commit 1422f28826d2 ("rds: introduce acquire/release ordering in acquire/release_in_xmit()") folded both into clear_bit_unlock(), which strengthened the lock hand-off but silently dropped the full barrier the wake-up check depends on. The refill counterpart, release_refill() in net/rds/ib_recv.c, still carries its smp_mb__after_atomic() for exactly this reason. Use wq_has_sleeper(), which is waitqueue_active() preceded by the required full barrier. Fixes: 1422f28826d2 ("rds: introduce acquire/release ordering in acquire/release_in_xmit()") Assisted-by: Claude-Code:claude-fable-5 Signed-off-by: Allison Henderson --- v3: unchanged v2: unchanged net/rds/send.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/net/rds/send.c b/net/rds/send.c index 15a1b97f13e7..8aad185e4b1a 100644 --- a/net/rds/send.c +++ b/net/rds/send.c @@ -114,8 +114,13 @@ static void release_in_xmit(struct rds_conn_path *cp) * hot path and finding waiters is very rare. We don't want to walk * the system-wide hashed waitqueue buckets in the fast path only to * almost never find waiters. + * + * wq_has_sleeper() supplies the full barrier that orders the wait + * queue read after the bit clear; clear_bit_unlock() alone is only + * a release and would let this check read a stale empty queue, + * losing the wake-up. */ - if (waitqueue_active(&cp->cp_waitq)) + if (wq_has_sleeper(&cp->cp_waitq)) wake_up_all(&cp->cp_waitq); } -- 2.25.1