On Wed, Dec 07, 2016 at 01:52:17PM +0000, Mark Rutland wrote: > Hi all > > Jeremy noticed a kernel lockup on arm64 when the perf tool was used in > parallel with hotplug, which I've reproduced on arm64 and x86(-64) with > v4.9-rc8. In both cases I'm using defconfig; I've tried enabling lockdep > but it was silent for arm64 and x86.
It looks like we're trying to install a task-bound event into a context where task_cpu(ctx->task) is dead, and thus the cpu_function_call() in perf_install_in_context() fails. We retry repeatedly. On !PREEMPT (as with x86 defconfig), we manage to prevent the hotplug machinery from making progress, and this turns into a livelock. On PREEMPT (as with arm64 defconfig), I'm somewhat lost. Thanks, Mark.
