Hi Michael,
It looks like this commit generates the following error:
stacktrace.c:(.text+0x1b0): undefined reference to `.smp_send_safe_nmi_ipi'
make[1]: *** [vmlinux] Error 1
make: *** [sub-make] Error 2
See http://kisskb.ellerman.id.au/kisskb/buildresult/13395345/ for details
Seems like that function only exists when CONFIG_NMI_IPI is defined.
Christophe
Le 02/05/2018 à 15:07, Michael Ellerman a écrit :
This allows eg. the RCU stall detector, or the soft/hardlockup
detectors to trigger a backtrace on all CPUs.
We implement this by sending a "safe" NMI, which will actually only
send an IPI. Unfortunately the generic code prints "NMI", so that's a
little confusing but we can probably live with it.
If one of the CPUs doesn't respond to the IPI, we then print some info
from it's paca and do a backtrace based on its saved_r1.
Example output:
INFO: rcu_sched detected stalls on CPUs/tasks:
2-...0: (0 ticks this GP) idle=1be/1/4611686018427387904
softirq=1055/1055 fqs=25735
(detected by 4, t=58847 jiffies, g=58, c=57, q=1258)
Sending NMI from CPU 4 to CPUs 2:
CPU 2 didn't respond to backtrace IPI, inspecting paca.
irq_soft_mask: 0x01 in_mce: 0 in_nmi: 0 current: 3623 (bash)
Back trace of paca->saved_r1 (0xc0000000e1c83ba0) (possibly stale):
Call Trace:
[c0000000e1c83ba0] [0000000000000014] 0x14 (unreliable)
[c0000000e1c83bc0] [c000000000765798] lkdtm_do_action+0x48/0x80
[c0000000e1c83bf0] [c000000000765a40] direct_entry+0x110/0x1b0
[c0000000e1c83c90] [c00000000058e650] full_proxy_write+0x90/0xe0
[c0000000e1c83ce0] [c0000000003aae3c] __vfs_write+0x6c/0x1f0
[c0000000e1c83d80] [c0000000003ab214] vfs_write+0xd4/0x240
[c0000000e1c83dd0] [c0000000003ab5cc] ksys_write+0x6c/0x110
[c0000000e1c83e30] [c00000000000b860] system_call+0x58/0x6c
Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
---
arch/powerpc/include/asm/nmi.h | 4 ++++
arch/powerpc/kernel/stacktrace.c | 51 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 55 insertions(+)
diff --git a/arch/powerpc/include/asm/nmi.h b/arch/powerpc/include/asm/nmi.h
index 9c80939b4d14..e97f58689ca7 100644
--- a/arch/powerpc/include/asm/nmi.h
+++ b/arch/powerpc/include/asm/nmi.h
@@ -4,6 +4,10 @@
#ifdef CONFIG_PPC_WATCHDOG
extern void arch_touch_nmi_watchdog(void);
+extern void arch_trigger_cpumask_backtrace(const cpumask_t *mask,
+ bool exclude_self);
+#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace
+
#else
static inline void arch_touch_nmi_watchdog(void) {}
#endif
diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index d534ed901538..cf4652d5df80 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -11,12 +11,15 @@
*/
#include <linux/export.h>
+#include <linux/nmi.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/stacktrace.h>
#include <asm/ptrace.h>
#include <asm/processor.h>
+#include <asm/paca.h>
+
/*
* Save stack-backtrace addresses into a stack_trace buffer.
*/
@@ -76,3 +79,51 @@ save_stack_trace_regs(struct pt_regs *regs, struct
stack_trace *trace)
save_context_stack(trace, regs->gpr[1], current, 0);
}
EXPORT_SYMBOL_GPL(save_stack_trace_regs);
+
+#ifdef CONFIG_PPC_BOOK3S_64
+static void handle_backtrace_ipi(struct pt_regs *regs)
+{
+ nmi_cpu_backtrace(regs);
+}
+
+static void raise_backtrace_ipi(cpumask_t *mask)
+{
+ unsigned int cpu;
+
+ for_each_cpu(cpu, mask) {
+ if (cpu == smp_processor_id())
+ handle_backtrace_ipi(NULL);
+ else
+ smp_send_safe_nmi_ipi(cpu, handle_backtrace_ipi, 5 *
USEC_PER_SEC);
+ }
+
+ for_each_cpu(cpu, mask) {
+ struct paca_struct *p = paca_ptrs[cpu];
+
+ cpumask_clear_cpu(cpu, mask);
+
+ pr_warn("CPU %d didn't respond to backtrace IPI, inspecting
paca.\n", cpu);
+ if (!virt_addr_valid(p)) {
+ pr_warn("paca pointer appears corrupt? (%px)\n", p);
+ continue;
+ }
+
+ pr_warn("irq_soft_mask: 0x%02x in_mce: %d in_nmi: %d",
+ p->irq_soft_mask, p->in_mce, p->in_nmi);
+
+ if (virt_addr_valid(p->__current))
+ pr_cont(" current: %d (%s)\n", p->__current->pid,
+ p->__current->comm);
+ else
+ pr_cont(" current pointer corrupt? (%px)\n",
p->__current);
+
+ pr_warn("Back trace of paca->saved_r1 (0x%016llx) (possibly
stale):\n", p->saved_r1);
+ show_stack(p->__current, (unsigned long *)p->saved_r1);
+ }
+}
+
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+{
+ nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace_ipi);
+}
+#endif /* CONFIG_PPC64 */
