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 D2E513AAF65; Fri, 28 Aug 2026 22:39:23 +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=1787956765; cv=none; b=OQXsR+L8pi2iZaVdxUVKWKtr/HnZqX/CLPUv4Er4/YQZcTO6D0CB+pgNHcbbJvn1VSk+7dGFwediLZVZ/bvehJS+/Rro7l4UvzaGZ7MOs1CyoqOvjl8rwcn+R2dmhYeYakgyQHJSfaQfK0ARRu2UIMx45P8WMmGcsBZ2macy2qc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787956765; c=relaxed/simple; bh=tlhlJjDuV2+Hd3V45TuBje/LfpvAOXx9gc8FMgArL3g=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=nb+yaIPVUdjYi+YUEjpGK/W4Ui3Jtc7rSeow047xJGzd+fZ+3Vh2O9PZ/abhZEz2jXT3qpkyv2lm65ES4uSx3rp0rvcm+FrOfHBSJMroWVmXBOF7PGfTmbScuRJkGBJ4U4TRGbXp+kveWVx4jWYmZpDZtADl25dmvGJUjF9LeTI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ObVQVVfE; 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="ObVQVVfE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C13C51F000E9; Fri, 28 Aug 2026 22:39:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787956763; bh=3zGxRDpcGUNVM+R6JDkZzDjaqMbArqGYKjBwMFqjUBE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ObVQVVfEHf80ume+cYRIEGt14ieyDANJ7siAEb9U6SBczBOGM808qi14dCX6vSte1 nTMjYTGaHsW60BaCuPm3Dbtjdk8tzksUfk5lohyaKmW/W7e7RG0DslM7mPDgKoSQOd UqC2C3v5725Ij35AT2vmp0NiAsObJxgC8yUIPVosn17PBC+sJaVGxUYjpux42fgkM5 hxKVYfP05Omv7dDVgwBbe3Qm8NTs8wz+24mxhzzMm1NfipdnYTmxPIiPcgzaCIJP5w 2osvR/0Z0eYxB6K+h6w0VGkZYCM1EOFsuyer8vKYlrDLilq1Ce6r4/hf6UgvNRHzPi p3fVH3vlSaqAg== 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 v5 1/7] net/rds: use wq_has_sleeper() in release_in_xmit() Date: Fri, 28 Aug 2026 15:39:15 -0700 Message-Id: <20260828223921.202913-2-achender@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260828223921.202913-1-achender@kernel.org> References: <20260828223921.202913-1-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 --- v5: no change since v4. 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