On Wed, Dec 02, 2020 at 11:16:05AM +0000, Mark Rutland wrote: > On Wed, Dec 02, 2020 at 11:56:49AM +0100, Heiko Carstens wrote: > > From 7bd86fb3eb039a4163281472ca79b9158e726526 Mon Sep 17 00:00:00 2001 > > From: Heiko Carstens <h...@linux.ibm.com> > > Date: Wed, 2 Dec 2020 11:46:01 +0100 > > Subject: [PATCH] s390: fix irq state tracing > > > > With commit 58c644ba512c ("sched/idle: Fix arch_cpu_idle() vs > > tracing") common code calls arch_cpu_idle() with a lockdep state that > > tells irqs are on. > > > > This doesn't work very well for s390: psw_idle() will enable interrupts > > to wait for an interrupt. As soon as an interrupt occurs the interrupt > > handler will verify if the old context was psw_idle(). If that is the > > case the interrupt enablement bits in the old program status word will > > be cleared. > > > > A subsequent test in both the external as well as the io interrupt > > handler checks if in the old context interrupts were enabled. Due to > > the above patching of the old program status word it is assumed the > > old context had interrupts disabled, and therefore a call to > > TRACE_IRQS_OFF (aka trace_hardirqs_off_caller) is skipped. Which in > > turn makes lockdep incorrectly "think" that interrupts are enabled > > within the interrupt handler. > > > > Fix this by unconditionally calling TRACE_IRQS_OFF when entering > > interrupt handlers. Also call unconditionally TRACE_IRQS_ON when > > leaving interrupts handlers. > > > > This leaves the special psw_idle() case, which now returns with > > interrupts disabled, but has an "irqs on" lockdep state. So callers of > > psw_idle() must adjust the state on their own, if required. This is > > currently only __udelay_disabled(). > > > > Fixes: 58c644ba512c ("sched/idle: Fix arch_cpu_idle() vs tracing") > > Signed-off-by: Heiko Carstens <h...@linux.ibm.com> > > FWIW, this makes sense to me from what I had to chase on the arm64 side, > and this seems happy atop v5.10-rc6 with all the lockdep and RCU debug > options enabled when booting to userspace under QEMU. > > Thanks, > Mark.
Thanks a lot for having a look and testing this!