When handling the Watchdog interrupt, long processing should not be done
while holding the __wd_smp_lock. This prevents the other CPUs to grab it
and to process Watchdog timer interrupts. Furhtermore, this could lead to
the following situation:
CPU x detect lockup on CPU y and grab the __wd_smp_lock
in watchdog_smp_panic()
CPU y caught the watchdog interrupt and try to grab the __wd_smp_lock
in soft_nmi_interrupt()
CPU x wait for CPU y to catch the IPI for 1s in __smp_send_nmi_ipi()
CPU x will timeout and so has spent 1s waiting while holding the
__wd_smp_lock.
A deadlock may also happen between the __wd_smp_lock and the console_owner
'lock' this way:
CPU x grab the console_owner
CPU y grab the __wd_smp_lock
CPU x catch the watchdog timer interrupt and needs to grab __wd_smp_lock
CPU y wants to print something and wait for console_owner
-> deadlock
Doing all the long processing without holding the _wd_smp_lock prevents
these situations.
Signed-off-by: Laurent Dufour <lduf...@linux.ibm.com>
---
arch/powerpc/kernel/watchdog.c | 31 +++++++++++++++++--------------
1 file changed, 17 insertions(+), 14 deletions(-)
diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
index f9ea0e5357f9..bc7411327066 100644
--- a/arch/powerpc/kernel/watchdog.c
+++ b/arch/powerpc/kernel/watchdog.c
@@ -149,6 +149,8 @@ static void set_cpu_stuck(int cpu, u64 tb)
static void watchdog_smp_panic(int cpu, u64 tb)
{
+ cpumask_t cpus_pending_copy;
+ u64 last_reset_tb_copy;
unsigned long flags;
int c;
@@ -161,29 +163,32 @@ static void watchdog_smp_panic(int cpu, u64 tb)
if (cpumask_weight(&wd_smp_cpus_pending) == 0)
goto out;
+ cpumask_copy(&cpus_pending_copy, &wd_smp_cpus_pending);
+ last_reset_tb_copy = wd_smp_last_reset_tb;
+
+ /* Take the stuck CPUs out of the watch group */
+ set_cpumask_stuck(&wd_smp_cpus_pending, tb);
+
+ wd_smp_unlock(&flags);
+
pr_emerg("CPU %d detected hard LOCKUP on other CPUs %*pbl\n",
- cpu, cpumask_pr_args(&wd_smp_cpus_pending));
+ cpu, cpumask_pr_args(&cpus_pending_copy));
pr_emerg("CPU %d TB:%lld, last SMP heartbeat TB:%lld (%lldms ago)\n",
- cpu, tb, wd_smp_last_reset_tb,
- tb_to_ns(tb - wd_smp_last_reset_tb) / 1000000);
+ cpu, tb, last_reset_tb_copy,
+ tb_to_ns(tb - last_reset_tb_copy) / 1000000);
if (!sysctl_hardlockup_all_cpu_backtrace) {
/*
* Try to trigger the stuck CPUs, unless we are going to
* get a backtrace on all of them anyway.
*/
- for_each_cpu(c, &wd_smp_cpus_pending) {
+ for_each_cpu(c, &cpus_pending_copy) {
if (c == cpu)
continue;
smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000);
}
}
- /* Take the stuck CPUs out of the watch group */
- set_cpumask_stuck(&wd_smp_cpus_pending, tb);
-
- wd_smp_unlock(&flags);
-
if (sysctl_hardlockup_all_cpu_backtrace)
trigger_allbutself_cpu_backtrace();
@@ -204,6 +209,8 @@ static void wd_smp_clear_cpu_pending(int cpu, u64 tb)
unsigned long flags;
wd_smp_lock(&flags);
+ cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck);
+ wd_smp_unlock(&flags);
pr_emerg("CPU %d became unstuck TB:%lld\n",
cpu, tb);
@@ -212,9 +219,6 @@ static void wd_smp_clear_cpu_pending(int cpu, u64 tb)
show_regs(regs);
else
dump_stack();
-
- cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck);
- wd_smp_unlock(&flags);
}
return;
}
@@ -267,6 +271,7 @@ DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt)
return 0;
}
set_cpu_stuck(cpu, tb);
+ wd_smp_unlock(&flags);
pr_emerg("CPU %d self-detected hard LOCKUP @ %pS\n",
cpu, (void *)regs->nip);
@@ -277,8 +282,6 @@ DEFINE_INTERRUPT_HANDLER_NMI(soft_nmi_interrupt)
print_irqtrace_events(current);
show_regs(regs);
- wd_smp_unlock(&flags);
-
if (sysctl_hardlockup_all_cpu_backtrace)
trigger_allbutself_cpu_backtrace();
--
2.33.1
