On Wed, Nov 25, 2020 at 10:45:17AM +0100, Marco Elver wrote: > On Tue, Nov 24, 2020 at 07:30PM +0000, Mark Rutland wrote: [...] > > > I noticed there are a bunch of warnings in the log > > > that might be relevant (see attached). > > > > > [ 91.184432] ============================= > > > [ 91.188301] WARNING: suspicious RCU usage > > > [ 91.192316] 5.10.0-rc4-next-20201119-00002-g51c2bf0ac853 #25 Tainted: G W > > > [ 91.197536] ----------------------------- > > > [ 91.201431] kernel/trace/trace_preemptirq.c:78 RCU not watching trace_hardirqs_off()! > > > [ 91.206546] > > > [ 91.206546] other info that might help us debug this: > > > [ 91.206546] > > > [ 91.211790] > > > [ 91.211790] rcu_scheduler_active = 2, debug_locks = 0 > > > [ 91.216454] RCU used illegally from extended quiescent state! > > > [ 91.220890] no locks held by swapper/0/0. > > > [ 91.224712] > > > [ 91.224712] stack backtrace: > > > [ 91.228794] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W 5.10.0-rc4-next-20201119-00002-g51c2bf0ac853 #25 > > > [ 91.234877] Hardware name: linux,dummy-virt (DT) > > > [ 91.239032] Call trace: > > > [ 91.242587] dump_backtrace+0x0/0x240 > > > [ 91.246500] show_stack+0x34/0x88 > > > [ 91.250295] dump_stack+0x140/0x1bc > > > [ 91.254159] lockdep_rcu_suspicious+0xe4/0xf8 > > > [ 91.258332] trace_hardirqs_off+0x214/0x330 > > > [ 91.262462] trace_graph_return+0x1ac/0x1d8 > > > [ 91.266564] ftrace_return_to_handler+0xa4/0x170 > > > [ 91.270809] return_to_handler+0x1c/0x38 > > > [ 91.274826] default_idle_call+0x94/0x38c > > > [ 91.278869] do_idle+0x240/0x290 > > > [ 91.282633] rest_init+0x1e8/0x2dc > > > [ 91.286529] arch_call_rest_init+0x1c/0x28 > > > [ 91.290585] start_kernel+0x638/0x670 > > > > Hmm... I suspect that arch_cpu_idle() is being traced here, and I reckon > > we have to mark that and its callees as noinstr, since it doesn't seem > > sane to have ftrace check whether RCU is watching for every function > > call. Maybe Paul or Steve can correct me. ;) > > Yes, it's arch_cpu_idle(). > > > If you still have the binary lying around, can you check whether > > default_idle_call+0x94/0x38c is just after the call to arch_cpu_idle()? > > If you could dump the asm around that, along with whatever faddr2line > > tells you, that'd be a great help. > > I reran to be sure, with similar results. I've attached a > syz-symbolize'd version of the warnings. Thanks for confirming, and for the symbolized report. I'll see about getting this fixed ASAP. Thanks, Mark.
