From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 031D413B285; Sun, 28 Jul 2024 15:45:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722181517; cv=none; b=Sq7LDAdosTJRjGWXgd2B2SJ4ttC28JuGXcfq+YL+a2VBM04k2V6wdqg/seVCad4f0peERCxPt9bOHoZWmrIyg/Nu6X+bKsCzVAGqc2OshPimf3rx5KLSgvk9zFj6qcSgtXN7/Wh8tpDNEggjouqw0q1QEnpL/r17eGaZVTAC3QQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722181517; c=relaxed/simple; bh=bW8puwp8UG1FE5R0NW0YGF8HexNK9uU3nHZPanPzjUI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ucg/TJU9OaGfesB0Wc39wvhsEKZznK/YqldDUwBhZDGFMHrjJePVb0ANzs1X+TMRllhrWIKRa+scHnXAJ553d3o62K8unsCznk9ISrb89A4Oncd8ZMqkPrLads1prvum/VLhTXRgxI7SHkuJYEA/74ladMxKSJNibQwYULdsSHo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UVm8DtU5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="UVm8DtU5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 02193C116B1; Sun, 28 Jul 2024 15:45:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1722181516; bh=bW8puwp8UG1FE5R0NW0YGF8HexNK9uU3nHZPanPzjUI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UVm8DtU5o8N/OdbJj9lgzpNYb2Ps1FcUHuMG9pVhJ2Ql6fNd5DW6MUDhoOFJ5+zPS pnuIqz6LtlPUQM2MWZeWtBroZl9VA7rR3lZrdvGnRDyK9BsSJ4xLH0rqRUweK98dsE WAwkGt4wUhk1aIG9k12YxouJBXBFrC4rERVJ5iP1WeNkLYm7ye/+BTnH65m4GI1QaI R1GTAEF1vzmBfxmhx4LhXcgpU6jP+z/N0HIJlbGng7PEPCJTn12I0adxx4ZceAqdFV 2Nt7VL3vQmtgN/joSwBEwPIiQ1YO80KozmPOfUacoJqR7gPtsU8jxltxrx7fa1LrIQ WZyqK3uu+UA5Q== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Benjamin Coddington , Jeff Layton , Anna Schumaker , Sasha Levin , chuck.lever@oracle.com, trondmy@kernel.org, anna@kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, linux-nfs@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH AUTOSEL 6.10 34/34] SUNRPC: Fix a race to wake a sync task Date: Sun, 28 Jul 2024 11:40:58 -0400 Message-ID: <20240728154230.2046786-34-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240728154230.2046786-1-sashal@kernel.org> References: <20240728154230.2046786-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.10.2 Content-Transfer-Encoding: 8bit From: Benjamin Coddington [ Upstream commit ed0172af5d6fc07d1b40ca82f5ca3979300369f7 ] We've observed NFS clients with sync tasks sleeping in __rpc_execute waiting on RPC_TASK_QUEUED that have not responded to a wake-up from rpc_make_runnable(). I suspect this problem usually goes unnoticed, because on a busy client the task will eventually be re-awoken by another task completion or xprt event. However, if the state manager is draining the slot table, a sync task missing a wake-up can result in a hung client. We've been able to prove that the waker in rpc_make_runnable() successfully calls wake_up_bit() (ie- there's no race to tk_runstate), but the wake_up_bit() call fails to wake the waiter. I suspect the waker is missing the load of the bit's wait_queue_head, so waitqueue_active() is false. There are some very helpful comments about this problem above wake_up_bit(), prepare_to_wait(), and waitqueue_active(). Fix this by inserting smp_mb__after_atomic() before the wake_up_bit(), which pairs with prepare_to_wait() calling set_current_state(). Signed-off-by: Benjamin Coddington Reviewed-by: Jeff Layton Signed-off-by: Anna Schumaker Signed-off-by: Sasha Levin --- net/sunrpc/sched.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c index 6debf4fd42d4e..cef623ea15060 100644 --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -369,8 +369,10 @@ static void rpc_make_runnable(struct workqueue_struct *wq, if (RPC_IS_ASYNC(task)) { INIT_WORK(&task->u.tk_work, rpc_async_schedule); queue_work(wq, &task->u.tk_work); - } else + } else { + smp_mb__after_atomic(); wake_up_bit(&task->tk_runstate, RPC_TASK_QUEUED); + } } /* -- 2.43.0