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Date: Thu, 22 Apr 2021 17:10:49 +0100 From: John Garry <john.garry@...wei.com> To: Thomas Gleixner <tglx@...utronix.de> CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Question on threaded handlers for managed interrupts Hi Thomas, I am finding that I can pretty easily trigger a system hang for certain scenarios with my storage controller. So I'm getting something like this when running moderately heavy data throughput: Starting 6 processes [70.656622] sched: RT throttling activatedB/s][r=356k,w=0 IOPS][eta 01h:14m:43s] [ 207.632161] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:ta 01h:12m:26s] [ 207.638261] rcu: 0-...!: (1 GPs behind) idle=312/1/0x4000000000000000 softirq=508/512 fqs=0 [ 207.646777] rcu: 1-...!: (1 GPs behind) idle=694/0/0x0 It ends pretty badly - see [0]. The multi-queue storage controller (see [1] for memory refresh, but note that I can also trigger on PCI device host controller as well) is using managed interrupts and threaded handlers. Since the threaded handler uses SCHED_FIFO, aren't we always vulnerable to this situation with the managed interrupt and threaded handler combo? Would the advice be to just use irq polling here? I unsuccessfully tried to trigger the same on NVMe PCI - however I have only 1x card, so hardly overloading the system. Thanks, John [0] https://lore.kernel.org/rcu/412926e8-d3e1-3071-8cb9-098a7f49b64c@huawei.com/T/#mbd60463c543e04f87090d89301e1a5f10de958dd [1] https://lore.kernel.org/linux-scsi/1606905417-183214-1-git-send-email-john.garry@huawei.com/#t
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