From a8c27c0bea45c6531fbc1e3be79ddd5a9bc1ba3e Mon Sep 17 00:00:00 2001 From: Rabin Vincent Date: Sun, 14 Jun 2015 19:26:11 +0200 Subject: [PATCH] mmc: queue: prevent soft lockups on PREEMPT=n 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 Signed-off-by: Ulf Hansson --- 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 d34e09b4161e..b5a2b145d89f 100644 --- a/drivers/mmc/card/queue.c +++ b/drivers/mmc/card/queue.c @@ -68,6 +68,7 @@ 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 */ -- 2.20.1