| Message ID | 20180502130729.24077-1-mpe@ellerman.id.au (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 7b08729cb272b4cd5c657cd5ac0dddae15a593ff |
| Headers | show |
| Series | [RFC,1/4] powerpc/64: Save stack pointer when we hard disable interrupts | expand |
On Wed, 2 May 2018 23:07:26 +1000 Michael Ellerman <mpe@ellerman.id.au> wrote: > A CPU that gets stuck with interrupts hard disable can be difficult to > debug, as on some platforms we have no way to interrupt the CPU to > find out what it's doing. > > A stop-gap is to have the CPU save it's stack pointer (r1) in its paca > when it hard disables interrupts. That way if we can't interrupt it, > we can at least trace the stack based on where it last disabled > interrupts. > > In some cases that will be total junk, but the stack trace code should > handle that. In the simple case of a CPU that disable interrupts and > then gets stuck in a loop, the stack trace should be informative. > > We could clear the saved stack pointer when we enable interrupts, but > that loses information which could be useful if we have nothing else > to go on. > > Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> > --- > arch/powerpc/include/asm/hw_irq.h | 6 +++++- > arch/powerpc/include/asm/paca.h | 2 +- > arch/powerpc/kernel/exceptions-64s.S | 1 + > arch/powerpc/xmon/xmon.c | 2 ++ > 4 files changed, 9 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h > index 855e17d158b1..35cb37be61fe 100644 > --- a/arch/powerpc/include/asm/hw_irq.h > +++ b/arch/powerpc/include/asm/hw_irq.h > @@ -237,8 +237,12 @@ static inline bool arch_irqs_disabled(void) > __hard_irq_disable(); \ > flags = irq_soft_mask_set_return(IRQS_ALL_DISABLED); \ > local_paca->irq_happened |= PACA_IRQ_HARD_DIS; \ > - if (!arch_irqs_disabled_flags(flags)) \ > + if (!arch_irqs_disabled_flags(flags)) { \ > + asm ("stdx %%r1, 0, %1 ;" \ > + : "=m" (local_paca->saved_r1) \ > + : "b" (&local_paca->saved_r1)); \ > trace_hardirqs_off(); \ > + } This is pretty neat, it would be good to have something that's not so destructive as the NMI IPI. Thanks, Nick
On Wed, 2018-05-02 at 13:07:26 UTC, Michael Ellerman wrote: > A CPU that gets stuck with interrupts hard disable can be difficult to > debug, as on some platforms we have no way to interrupt the CPU to > find out what it's doing. > > A stop-gap is to have the CPU save it's stack pointer (r1) in its paca > when it hard disables interrupts. That way if we can't interrupt it, > we can at least trace the stack based on where it last disabled > interrupts. > > In some cases that will be total junk, but the stack trace code should > handle that. In the simple case of a CPU that disable interrupts and > then gets stuck in a loop, the stack trace should be informative. > > We could clear the saved stack pointer when we enable interrupts, but > that loses information which could be useful if we have nothing else > to go on. > > Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Series applied to powerpc next. https://git.kernel.org/powerpc/c/7b08729cb272b4cd5c657cd5ac0ddd cheers
diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h index 855e17d158b1..35cb37be61fe 100644 --- a/arch/powerpc/include/asm/hw_irq.h +++ b/arch/powerpc/include/asm/hw_irq.h @@ -237,8 +237,12 @@ static inline bool arch_irqs_disabled(void) __hard_irq_disable(); \ flags = irq_soft_mask_set_return(IRQS_ALL_DISABLED); \ local_paca->irq_happened |= PACA_IRQ_HARD_DIS; \ - if (!arch_irqs_disabled_flags(flags)) \ + if (!arch_irqs_disabled_flags(flags)) { \ + asm ("stdx %%r1, 0, %1 ;" \ + : "=m" (local_paca->saved_r1) \ + : "b" (&local_paca->saved_r1)); \ trace_hardirqs_off(); \ + } \ } while(0) static inline bool lazy_irq_pending(void) diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h index 3f109a3e3edb..e7814d948c7a 100644 --- a/arch/powerpc/include/asm/paca.h +++ b/arch/powerpc/include/asm/paca.h @@ -161,7 +161,7 @@ struct paca_struct { struct task_struct *__current; /* Pointer to current */ u64 kstack; /* Saved Kernel stack addr */ u64 stab_rr; /* stab/slb round-robin counter */ - u64 saved_r1; /* r1 save for RTAS calls or PM */ + u64 saved_r1; /* r1 save for RTAS calls or PM or EE=0 */ u64 saved_msr; /* MSR saved here by enter_rtas */ u16 trap_save; /* Used when bad stack is encountered */ u8 irq_soft_mask; /* mask for irq soft masking */ diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index ae6a849db60b..bb26fe9e90ce 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -1499,6 +1499,7 @@ masked_##_H##interrupt: \ xori r10,r10,MSR_EE; /* clear MSR_EE */ \ mtspr SPRN_##_H##SRR1,r10; \ 2: mtcrf 0x80,r9; \ + std r1,PACAR1(r13); \ ld r9,PACA_EXGEN+EX_R9(r13); \ ld r10,PACA_EXGEN+EX_R10(r13); \ ld r11,PACA_EXGEN+EX_R11(r13); \ diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c index a0842f1ff72c..94cc8ba36c14 100644 --- a/arch/powerpc/xmon/xmon.c +++ b/arch/powerpc/xmon/xmon.c @@ -1161,6 +1161,8 @@ static int cpu_cmd(void) /* try to switch to cpu specified */ if (!cpumask_test_cpu(cpu, &cpus_in_xmon)) { printf("cpu 0x%x isn't in xmon\n", cpu); + printf("backtrace of paca[0x%x].saved_r1 (possibly stale):\n", cpu); + xmon_show_stack(paca_ptrs[cpu]->saved_r1, 0, 0); return 0; } xmon_taken = 0;
A CPU that gets stuck with interrupts hard disable can be difficult to debug, as on some platforms we have no way to interrupt the CPU to find out what it's doing. A stop-gap is to have the CPU save it's stack pointer (r1) in its paca when it hard disables interrupts. That way if we can't interrupt it, we can at least trace the stack based on where it last disabled interrupts. In some cases that will be total junk, but the stack trace code should handle that. In the simple case of a CPU that disable interrupts and then gets stuck in a loop, the stack trace should be informative. We could clear the saved stack pointer when we enable interrupts, but that loses information which could be useful if we have nothing else to go on. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> --- arch/powerpc/include/asm/hw_irq.h | 6 +++++- arch/powerpc/include/asm/paca.h | 2 +- arch/powerpc/kernel/exceptions-64s.S | 1 + arch/powerpc/xmon/xmon.c | 2 ++ 4 files changed, 9 insertions(+), 2 deletions(-)