Messages in this thread | | | Date | Wed, 2 Dec 2020 11:16:05 +0000 | From | Mark Rutland <> | Subject | Re: [GIT pull] locking/urgent for v5.10-rc6 |
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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 <hca@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 <hca@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.
> --- > arch/s390/kernel/entry.S | 15 --------------- > arch/s390/lib/delay.c | 5 ++--- > 2 files changed, 2 insertions(+), 18 deletions(-) > > diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S > index 26bb0603c5a1..92beb1444644 100644 > --- a/arch/s390/kernel/entry.S > +++ b/arch/s390/kernel/entry.S > @@ -763,12 +763,7 @@ ENTRY(io_int_handler) > xc __PT_FLAGS(8,%r11),__PT_FLAGS(%r11) > TSTMSK __LC_CPU_FLAGS,_CIF_IGNORE_IRQ > jo .Lio_restore > -#if IS_ENABLED(CONFIG_TRACE_IRQFLAGS) > - tmhh %r8,0x300 > - jz 1f > TRACE_IRQS_OFF > -1: > -#endif > xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15) > .Lio_loop: > lgr %r2,%r11 # pass pointer to pt_regs > @@ -791,12 +786,7 @@ ENTRY(io_int_handler) > TSTMSK __LC_CPU_FLAGS,_CIF_WORK > jnz .Lio_work > .Lio_restore: > -#if IS_ENABLED(CONFIG_TRACE_IRQFLAGS) > - tm __PT_PSW(%r11),3 > - jno 0f > TRACE_IRQS_ON > -0: > -#endif > mvc __LC_RETURN_PSW(16),__PT_PSW(%r11) > tm __PT_PSW+1(%r11),0x01 # returning to user ? > jno .Lio_exit_kernel > @@ -976,12 +966,7 @@ ENTRY(ext_int_handler) > xc __PT_FLAGS(8,%r11),__PT_FLAGS(%r11) > TSTMSK __LC_CPU_FLAGS,_CIF_IGNORE_IRQ > jo .Lio_restore > -#if IS_ENABLED(CONFIG_TRACE_IRQFLAGS) > - tmhh %r8,0x300 > - jz 1f > TRACE_IRQS_OFF > -1: > -#endif > xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15) > lgr %r2,%r11 # pass pointer to pt_regs > lghi %r3,EXT_INTERRUPT > diff --git a/arch/s390/lib/delay.c b/arch/s390/lib/delay.c > index daca7bad66de..8c0c68e7770e 100644 > --- a/arch/s390/lib/delay.c > +++ b/arch/s390/lib/delay.c > @@ -33,7 +33,7 @@ EXPORT_SYMBOL(__delay); > > static void __udelay_disabled(unsigned long long usecs) > { > - unsigned long cr0, cr0_new, psw_mask, flags; > + unsigned long cr0, cr0_new, psw_mask; > struct s390_idle_data idle; > u64 end; > > @@ -45,9 +45,8 @@ static void __udelay_disabled(unsigned long long usecs) > psw_mask = __extract_psw() | PSW_MASK_EXT | PSW_MASK_WAIT; > set_clock_comparator(end); > set_cpu_flag(CIF_IGNORE_IRQ); > - local_irq_save(flags); > psw_idle(&idle, psw_mask); > - local_irq_restore(flags); > + trace_hardirqs_off(); > clear_cpu_flag(CIF_IGNORE_IRQ); > set_clock_comparator(S390_lowcore.clock_comparator); > __ctl_load(cr0, 0, 0); > -- > 2.17.1 >
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