From: Pavankumar Kondeti <pkondeti@xxxxxxxxxxxxxx> commit c59f29cb144a6a0dfac16ede9dc8eafc02dc56ca upstream. The 's' flag is supposed to indicate that a softirq is running. This can be detected by testing the preempt_count with SOFTIRQ_OFFSET. The current code tests the preempt_count with SOFTIRQ_MASK, which would be true even when softirqs are disabled but not serving a softirq. Link: http://lkml.kernel.org/r/1481300417-3564-1-git-send-email-pkondeti@xxxxxxxxxxxxxx Signed-off-by: Pavankumar Kondeti <pkondeti@xxxxxxxxxxxxxx> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> Signed-off-by: Amit Pundir <amit.pundir@xxxxxxxxxx> --- This upstream patch fixed a CPU soft lockup and rcu stall bug reported on linux-4.9.y while running ftracetest on Hikey, with usb-ethernet plugged-in but not connected to any network. Bug can be reproduced and fixed on linux-4.4.y as well. Most likely applicable for linux-3.18.y too but I couldn't boot up hikey with 3.18 kernel. Here is the bug report: https://bugs.linaro.org/show_bug.cgi?id=3034 kernel/trace/trace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 6011148b0239..49d086753a0b 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -1927,7 +1927,7 @@ tracing_generic_entry_update(struct trace_entry *entry, unsigned long flags, #endif ((pc & NMI_MASK ) ? TRACE_FLAG_NMI : 0) | ((pc & HARDIRQ_MASK) ? TRACE_FLAG_HARDIRQ : 0) | - ((pc & SOFTIRQ_MASK) ? TRACE_FLAG_SOFTIRQ : 0) | + ((pc & SOFTIRQ_OFFSET) ? TRACE_FLAG_SOFTIRQ : 0) | (tif_need_resched() ? TRACE_FLAG_NEED_RESCHED : 0) | (test_preempt_need_resched() ? TRACE_FLAG_PREEMPT_RESCHED : 0); } -- 2.7.4