On Fri, 2017-03-17 at 15:33 +0000, Mark Rutland wrote: > > We can certainly log a better message, e.g. > > bool kdump = (image == kexec_crash_image); > bool stuck_cpus = cpus_are_stuck_in_kernel() || > num_online_cpus() > 1; > > BUG_ON(stuck_cpus && !kdump); > WARN(stuck_cpus, "Unable to offline CPUs, kdump will be > unreliable.\n");
No, in this case the CPUs *were* offlined correctly, or at least "as
designed", by smp_send_crash_stop(). And if that hadn't worked, as
verified by *its* synchronisation method based on the atomic_t
waiting_for_crash_ipi, then *it* would have complained for itself:
if (atomic_read(&waiting_for_crash_ipi) > 0)
pr_warning("SMP: failed to stop secondary CPUs %*pbl\n",
cpumask_pr_args(cpu_online_mask));
It's just that smp_send_crash_stop() (or more specifically
ipi_cpu_crash_stop()) doesn't touch the online cpu mask. Unlike the
ARM32 equivalent function machien_crash_nonpanic_core(), which does.
It wasn't clear if that was *intentional*, to allow the original
contents of the online mask before the crash to be seen in the
resulting vmcore... or purely an accident.
FWIW if I trigger a crash on CPU 1 my kdump (still 4.9.8+v32) doesn't work.
I end up booting the kdump kernel on CPU#1 and then it gets distinctly
unhappy...
[ 0.000000] Booting Linux on physical CPU 0x1
...
[ 0.017125] Detected PIPT I-cache on CPU1
[ 0.017138] GICv3: CPU1: found redistributor 0 region 0:0x00000000f0280000
[ 0.017147] CPU1: Booted secondary processor [411fd073]
[ 0.017339] Detected PIPT I-cache on CPU2
[ 0.017347] GICv3: CPU2: found redistributor 2 region 0:0x00000000f02c0000
[ 0.017354] CPU2: Booted secondary processor [411fd073]
[ 0.017537] Detected PIPT I-cache on CPU3
[ 0.017545] GICv3: CPU3: found redistributor 3 region 0:0x00000000f02e0000
[ 0.017551] CPU3: Booted secondary processor [411fd073]
[ 0.017576] Brought up 4 CPUs
[ 0.017587] SMP: Total of 4 processors activated.
...
[ 31.745809] INFO: rcu_sched detected stalls on CPUs/tasks:
[ 31.751299] 1-...: (30 GPs behind) idle=c90/0/0 softirq=0/0 fqs=0
[ 31.757557] 2-...: (30 GPs behind) idle=608/0/0 softirq=0/0 fqs=0
[ 31.763814] 3-...: (30 GPs behind) idle=604/0/0 softirq=0/0 fqs=0
[ 31.770069] (detected by 0, t=5252 jiffies, g=-270, c=-271, q=0)
[ 31.776161] Task dump for CPU 1:
[ 31.779381] swapper/1 R running task 0 0 1 0x00000080
[ 31.786446] Task dump for CPU 2:
[ 31.789666] swapper/2 R running task 0 0 1 0x00000080
[ 31.796725] Task dump for CPU 3:
[ 31.799945] swapper/3 R running task 0 0 1 0x00000080
Is some of that platform-specific?
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 701c085..41d238e 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -129,7 +129,7 @@ static struct sysrq_key_op sysrq_unraw_op = {
#define sysrq_unraw_op (*(struct sysrq_key_op *)NULL)
#endif /* CONFIG_VT */
-static void sysrq_handle_crash(int key)
+static void do_sysrq_handle_crash(int key)
{
char *killer = NULL;
@@ -143,6 +143,12 @@ static void sysrq_handle_crash(int key)
wmb();
*killer = 1;
}
+
+static void sysrq_handle_crash(int key)
+{
+ smp_call_on_cpu(1, (void *)do_sysrq_handle_crash, 0, 1);
+}
+
static struct sysrq_key_op sysrq_crash_op = {
.handler = sysrq_handle_crash,
.help_msg = "crash(c)",
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