Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752462AbbFNR00 (ORCPT ); Sun, 14 Jun 2015 13:26:26 -0400 Received: from bastet.se.axis.com ([195.60.68.11]:50641 "EHLO bastet.se.axis.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751982AbbFNR0S (ORCPT ); Sun, 14 Jun 2015 13:26:18 -0400 From: Rabin Vincent To: CC: , , Rabin Vincent Subject: [PATCH] mmc: queue: prevent soft lockups on PREEMPT=n Date: Sun, 14 Jun 2015 19:26:11 +0200 Message-ID: <1434302771-9599-1-git-send-email-rabin.vincent@axis.com> X-Mailer: git-send-email 1.7.10.4 MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2087 Lines: 48 On systems with CONFIG_PREEMPT=n, under certain circumstances, mmcqd can continuously process requests for several seconds without blocking, triggering the soft lockup watchdog. For example, this can happen if mmcqd runs on the CPU which services the controller's interrupt, and a process on a different CPU continuously writes to the MMC block device. NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [mmcqd/0:664] CPU: 0 PID: 664 Comm: mmcqd/0 Not tainted 4.1.0-rc7+ #4 PC is at _raw_spin_unlock_irqrestore+0x24/0x28 LR is at mmc_start_request+0x104/0x134 ... [<805112a8>] (_raw_spin_unlock_irqrestore) from [<803db664>] (mmc_start_request+0x104/0x134) [<803db664>] (mmc_start_request) from [<803dc008>] (mmc_start_req+0x274/0x394) [<803dc008>] (mmc_start_req) from [<803eb2c4>] (mmc_blk_issue_rw_rq+0xd0/0xb98) [<803eb2c4>] (mmc_blk_issue_rw_rq) from [<803ebe8c>] (mmc_blk_issue_rq+0x100/0x470) [<803ebe8c>] (mmc_blk_issue_rq) from [<803ecab8>] (mmc_queue_thread+0xd0/0x170) [<803ecab8>] (mmc_queue_thread) from [<8003fd14>] (kthread+0xe0/0xfc) [<8003fd14>] (kthread) from [<8000f768>] (ret_from_fork+0x14/0x2c) Fix it by adding a cond_resched() in the request handling loop so that other processes get a chance to run. Signed-off-by: Rabin Vincent --- drivers/mmc/card/queue.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c index 8efa368..e78ae97 100644 --- a/drivers/mmc/card/queue.c +++ b/drivers/mmc/card/queue.c @@ -69,6 +69,7 @@ static int mmc_queue_thread(void *d) set_current_state(TASK_RUNNING); cmd_flags = req ? req->cmd_flags : 0; mq->issue_fn(mq, req); + cond_resched(); if (mq->flags & MMC_QUEUE_NEW_REQUEST) { mq->flags &= ~MMC_QUEUE_NEW_REQUEST; continue; /* fetch again */ -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/