From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793740821; b=hMSVRBTvO5uIY7EX3fhLCUaL4wu3g8t1C+Jf6oJbq9zlsGijz5EkPpJ05+byBEqM0Ncv xySkAiBqgIf9Y0Nvd1CY16tqC7IInmqM1oo4EBUKmops1+q9GkwR0KxaV87DrvKIphFQz bGDEN85B/mrO2LIxKPtx3Hhd5Mh7NkiIhst/MrdlgnSHoiHOZfuxMO3RcZgm70ne6sawf bNIbug0SW56PJgDUBJxpcH+8u4zv58sCuX+7MyG1qGDONwJPxnQsIv2A8+LZ+3oGo0NVH Cxdz44Z6UKpgb1XoGI5z/aPsx+0c/oae53f97EPlXzWXbuC21uPBRC+ftKds/WBn7bw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793740821; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:X-B4-Tracking:X-Change-ID:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=JE6RFDaW5iJIlTyYoNr0dPdQqfpRddHdFnlHhfF7/Q0=; b=D6N5LFBNfKVkR3xOCX7mmev7C3gqR98s+x2MS70yFtnFz/6ERQYcuHJLGkGgyorPov19 npgJABbboOXRMnm4QM/Fac8ZyFUakNJzl8dtv6zP360Ih/XvO+QPfq8teC+M3kj3tg/Xh wMA/6/wYx854xLSOceeYBruMyucvTWmGcRM4hf+HZltLMCHGtS0iqM8NO8WutJUnKKQNY 6P06WXyGmutGEZAWnMNAxae3VPuYR/A8MGgZxIZhitzT3k+Sf7KzzcECB+41enD5njQgx Jc2qSKbD5Kq42lwef0ONEKDR8GYRgUZj7qiVqeDnVBh6B0fMmJ/17PsOo7KOqzxq+vg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="DhGTW+B/"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3CB16606A32F; Tue, 3 Nov 2026 21:20:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=DhGTW+B/ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3E6921F00919; Tue, 3 Nov 2026 21:20:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793740820; bh=JE6RFDaW5iJIlTyYoNr0dPdQqfpRddHdFnlHhfF7/Q0=; h=From:Date:Subject:To:Cc; b=DhGTW+B/P+yFX4vqQgWvO8IVvSjn6KQ+ZzMdmgBc662BxpH7qQMDimpSgutf0XPPx fKRpVApM438sTSUNZWX5ZLC1P4UbbpDhg/n/bzxl6zVITBTYjXQcmzTe7xEbrrHic2 q5pukV5U53rK6C62SDmZhYL5kejLGAjc3Sh9iAe7xkMU9ac6Sew/ylPy+NWyFyS3iz yzagEp9qs4QoJpm93TndQpbx/jO4cmg4ocUuZL6Sx+KP8h/11JIls1h8XnUNokdyz8 I6tFsz8ODSgqsy1eLIS1myjynahDXlzBcUK8tHXEZWFPD0GmZhlZr7lqB2yJiVCvoy KCwo/78iaqBKA== From: Eugen Hristev Date: Tue, 03 Nov 2026 23:20:12 +0200 Subject: [PATCH v2] PCI: iproc-msi: Removed potentially endless loop handling MSI events X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Message-Id: <20261103-iproc-irq-v2-1-dc7223df35fc@kernel.org> X-B4-Tracking: v=1; b=H4sIAAtQ6moC/22NQQ6CMBAAv0L2bA2tAakn/2E4lLqFVUNxi42G9 O8WvHqcZDKzQEAmDHAqFmCMFMiPGdSuADuYsUdB18ygSlXLUtaCJvZWED+FtlVjHR60rBrI/sT o6L21Lu2Pw6u7oZ3XwGoMFGbPn20W5er960YppMDOGFeqo1Maz3fkER97zz20KaUvYGwa87UAA AA= X-Change-ID: 20261016-iproc-irq-9c58cfe39158 To: Lorenzo Pieralisi , =?utf-8?q?Krzysztof_Wilczy=C5=84ski?= , Manivannan Sadhasivam , Rob Herring , Bjorn Helgaas , Ray Jui , Scott Branden , Broadcom internal kernel review list Cc: linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Eugen Hristev X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=5460; i=ehristev@kernel.org; h=from:subject:message-id; bh=pAhFkgivPGa8+WZMgqY+OKupz5W/lxtX/1KCdlqX2/E=; b=owGbwMvMwCXWkjcnuXne3fmMp9WSGLJeBfAd2Lbwau9e9zfcQcfOrZ9psPrNka1nhJw3HU1L+ rnhQI/Yio5SFgYxLgZZMUWWapN/tcL9O9xPulqqwMxhZQIZwsDFKQAT2X+RkWHyP+bSM1znXrDF b/HjqrVlrBZlvW9aO3tp9cTDJ9W+ljAzMjS2rWDepMbxQdbLPCYquSDSw33JlrcBJYXXz7xpnuw ixwEA X-Developer-Key: i=ehristev@kernel.org; a=openpgp; fpr=AB184498D27A77B65D7852C81EB31E020EAC2FC8 The iProc MSI chained handler rereads the event queue tail after each batch and keeps processing until the queue is empty. A continuously fed queue can therefore keep the CPU in the handler indefinitely, starving other interrupts and causing RCU stalls under heavy Ethernet traffic. To fix this scenario, remove the loop that keeps reading the head and the tail until there are no more pending events. Read the head and tail only once and process only the events recorded in that snapshot. Update the head before returning. Events arriving during processing remain queued for a subsequent parent interrupt, allowing other handlers to run without imposing an arbitrary event limit. Discovered while testing it with an Ethernet NIC, when too many MSI interrupts come in, CPU might get starved: Connecting to host 192.168.30.1, port 5201 [ 5] local 192.168.30.2 port 52586 connected to 192.168.30.1 port 5201 [ ID] Interval Transfer Bitrate Retr Cwnd [ 5] 0.00-1.00 sec 240 MBytes 2.01 Gbits/sec 2 334 KBytes [ 5] 1.00-2.00 sec 63.2 MBytes 531 Mbits/sec 1 1.41 KBytes [ 5] 2.00-3.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes [ 5] 3.00-4.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes [ 5] 4.00-5.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes [ 5] 5.00-6.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes [ 5] 6.00-7.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes [ 5] 7.00-8.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes [ 5] 8.00-9.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes [ 177.568497] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: [ 177.568913] rcu: 0-...!: (1 GPs behind) idle=28ac/1/0x4000000000000002 softirq=28922/28930 fqs=1 [ 177.569457] rcu: (detected by 1, t=5256 jiffies, g=21629, q=819 ncpus=4) [ 177.569870] Sending NMI from CPU 1 to CPUs 0: With this one loop approach, IRQ handler will complete and continue to serve MSI events on the next handler invocation. Signed-off-by: Eugen Hristev --- Changes in v2: - Changed as per suggestion from Mani: removed the budget and completely removed the do/while(true) loop - Link to v1: https://patch.msgid.link/20261016-iproc-irq-v1-1-ebaaf027f29e@kernel.org To: Lorenzo Pieralisi To: Krzysztof Wilczyński To: Manivannan Sadhasivam To: Rob Herring To: Bjorn Helgaas To: Ray Jui To: Scott Branden To: Broadcom internal kernel review list Cc: linux-pci@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org --- drivers/pci/controller/pcie-iproc-msi.c | 61 ++++++++++++++++----------------- 1 file changed, 29 insertions(+), 32 deletions(-) diff --git a/drivers/pci/controller/pcie-iproc-msi.c b/drivers/pci/controller/pcie-iproc-msi.c index 9ba242ab9596..86753ae75ed3 100644 --- a/drivers/pci/controller/pcie-iproc-msi.c +++ b/drivers/pci/controller/pcie-iproc-msi.c @@ -344,42 +344,39 @@ static void iproc_msi_handler(struct irq_desc *desc) * data is guaranteed to be in the event queue memory before the tail * pointer is updated by the iProc MSI core. */ - head = iproc_msi_read_reg(msi, IPROC_MSI_EQ_HEAD, - eq) & IPROC_MSI_EQ_MASK; - do { - tail = iproc_msi_read_reg(msi, IPROC_MSI_EQ_TAIL, - eq) & IPROC_MSI_EQ_MASK; + head = iproc_msi_read_reg(msi, IPROC_MSI_EQ_HEAD, eq) & + IPROC_MSI_EQ_MASK; + tail = iproc_msi_read_reg(msi, IPROC_MSI_EQ_TAIL, eq) & + IPROC_MSI_EQ_MASK; - /* - * Figure out total number of events (MSI data) to be - * processed. - */ - nr_events = (tail < head) ? - (EQ_LEN - (head - tail)) : (tail - head); - if (!nr_events) - break; - - /* process all outstanding events */ - while (nr_events--) { - hwirq = decode_msi_hwirq(msi, eq, head); - generic_handle_domain_irq(msi->inner_domain, hwirq); - - head++; - head %= EQ_LEN; - } + /* + * Figure out total number of events (MSI data) to be + * processed. + */ + nr_events = (tail < head) ? (EQ_LEN - (head - tail)) : (tail - head); + if (!nr_events) + goto iproc_msi_handler_out; - /* - * Now all outstanding events have been processed. Update the - * head pointer. - */ - iproc_msi_write_reg(msi, IPROC_MSI_EQ_HEAD, eq, head); + /* process all outstanding events */ + while (nr_events--) { + hwirq = decode_msi_hwirq(msi, eq, head); + generic_handle_domain_irq(msi->inner_domain, hwirq); - /* - * Now go read the tail pointer again to see if there are new - * outstanding events that came in during the above window. - */ - } while (true); + head++; + head %= EQ_LEN; + } + /* + * Now all outstanding events have been processed. Update the + * head pointer. + */ + iproc_msi_write_reg(msi, IPROC_MSI_EQ_HEAD, eq, head); + + /* + * The tail pointer will be reread on the next interrupt to process + * any new events that arrived while handling this batch. + */ +iproc_msi_handler_out: chained_irq_exit(chip, desc); } --- base-commit: b810335a0699d1810683796b0e3ffe8827ddfe6c change-id: 20261016-iproc-irq-9c58cfe39158 Best regards, -- Eugen Hristev