smp_send_stop can lock up the IPI path for any subsequent calls,
because the receiving CPUs spin in their handler function. This
started becoming a problem with the addition of an smp_send_stop
call in the reboot path, because panics can reboot after doing
their own smp_send_stop.
The NMI IPI variant was fixed with ac61c11566 ("powerpc: Fix
smp_send_stop NMI IPI handling"), which leaves the smp_call_function
variant.
This is fixed by having smp_send_stop only ever do the
smp_call_function once. This is a bit less robust than the NMI IPI
fix, because any other call to smp_call_function after smp_send_stop
could deadlock, but that has always been the case, and it was not
been a problem before.
Cc: Michael Ellerman <m...@ellerman.id.au>
Fixes: f2748bdfe1573 ("powerpc/powernv: Always stop secondaries before
reboot/shutdown")
Reported-by: Abdul Haleem <abdha...@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
Changes since v1:
- Rebased to powerpc fixes branch which has the NMI IPI fix.
arch/powerpc/kernel/smp.c | 55 +++++++++++++++++++++++++++------------
1 file changed, 39 insertions(+), 16 deletions(-)
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 3582f30b60b7..9ca7148b5881 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -565,17 +565,6 @@ void crash_send_ipi(void (*crash_ipi_callback)(struct
pt_regs *))
}
#endif
-static void stop_this_cpu(void *dummy)
-{
- /* Remove this CPU */
- set_cpu_online(smp_processor_id(), false);
-
- hard_irq_disable();
- spin_begin();
- while (1)
- spin_cpu_relax();
-}
-
#ifdef CONFIG_NMI_IPI
static void nmi_stop_this_cpu(struct pt_regs *regs)
{
@@ -583,23 +572,57 @@ static void nmi_stop_this_cpu(struct pt_regs *regs)
* This is a special case because it never returns, so the NMI IPI
* handling would never mark it as done, which makes any later
* smp_send_nmi_ipi() call spin forever. Mark it done now.
+ *
+ * IRQs are already hard disabled by the smp_handle_nmi_ipi.
*/
nmi_ipi_lock();
nmi_ipi_busy_count--;
nmi_ipi_unlock();
- stop_this_cpu(NULL);
+ /* Remove this CPU */
+ set_cpu_online(smp_processor_id(), false);
+
+ spin_begin();
+ while (1)
+ spin_cpu_relax();
}
-#endif
void smp_send_stop(void)
{
-#ifdef CONFIG_NMI_IPI
smp_send_nmi_ipi(NMI_IPI_ALL_OTHERS, nmi_stop_this_cpu, 1000000);
-#else
+}
+
+#else /* CONFIG_NMI_IPI */
+
+static void stop_this_cpu(void *dummy)
+{
+ /* Remove this CPU */
+ set_cpu_online(smp_processor_id(), false);
+
+ hard_irq_disable();
+ spin_begin();
+ while (1)
+ spin_cpu_relax();
+}
+
+void smp_send_stop(void)
+{
+ static bool stopped = false;
+
+ /*
+ * Prevent waiting on csd lock from a previous smp_send_stop.
+ * This is racy, but in general callers try to do the right
+ * thing and only fire off one smp_send_stop (e.g., see
+ * kernel/panic.c)
+ */
+ if (stopped)
+ return;
+
+ stopped = true;
+
smp_call_function(stop_this_cpu, NULL, 0);
-#endif
}
+#endif /* CONFIG_NMI_IPI */
struct thread_info *current_set[NR_CPUS];
--
2.17.0
