This patch fixes one of the problems reported by Daniel Walker
(https://lkml.org/lkml/2015/6/24/44).
If "crash_kexec_post_notifiers" boot option is specified,
other cpus are stopped by smp_send_stop() before entering
crash_kexec(), while usually machine_crash_shutdown() called by
crash_kexec() does that. This behavior change leads two problems.
Problem 1:
Some functions in the crash_kexec() path depend on other cpus being
still online. If other cpus have been offlined already, they
doesn't work properly.
Example (MIPS OCTEON case):
panic()
crash_kexec()
machine_crash_shutdown()
octeon_generic_shutdown() // shutdown watchdog for ONLINE cpus
machine_kexec()
Problem 2:
Most of architectures stop other cpus in the machine_crash_shutdown()
path and save register information at that time. However, if
smp_send_stop() is called before that, we can't save the register
information.
This patch solves the problem 2 by replacing smp_send_stop() in
panic() with panic_smp_stop_cpus() which is a weak function and can be
replaced with suitable version for crash_kexec context. In fact,
x86 replaces it with a function based on kdump_nmi_shootdown_cpus() to
stop other cpus and save their states.
Please note that crash_kexec() can be called directly without
entering panic(). A stop-other-cpus procedure is still needed
by crash_kexec().
Changes in V2:
- Replace smp_send_stop() call with crash_kexec version which
saves cpu states and cleans up VMX/SVM
- Drop a fix for Problem 1 at this moment
Reported-by: Daniel Walker <[email protected]>
Fixes: f06e5153f4ae (kernel/panic.c: add "crash_kexec_post_notifiers" option
Signed-off-by: Hidehiro Kawai <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Eric Biederman <[email protected]>
Cc: Vivek Goyal <[email protected]>
---
arch/x86/kernel/crash.c | 16 +++++++++++-----
kernel/panic.c | 29 +++++++++++++++++++++++------
2 files changed, 34 insertions(+), 11 deletions(-)
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index e068d66..913c621 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -130,16 +130,22 @@ static void kdump_nmi_callback(int cpu, struct pt_regs
*regs)
disable_local_APIC();
}
-static void kdump_nmi_shootdown_cpus(void)
+/* Please see the comment on the weak version in kernel/panic.c */
+void panic_smp_stop_cpus(void)
{
+ static int cpus_stopped;
+
in_crash_kexec = 1;
- nmi_shootdown_cpus(kdump_nmi_callback);
- disable_local_APIC();
+ if (!cpus_stopped) {
+ nmi_shootdown_cpus(kdump_nmi_callback);
+ disable_local_APIC();
+ cpus_stopped = 1;
+ }
}
#else
-static void kdump_nmi_shootdown_cpus(void)
+void panic_smp_stop_cpus(void)
{
/* There are no cpus to shootdown */
}
@@ -158,7 +164,7 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
/* The kernel is broken so disable interrupts */
local_irq_disable();
- kdump_nmi_shootdown_cpus();
+ panic_smp_stop_cpus();
/*
* VMCLEAR VMCSs loaded on this cpu if needed.
diff --git a/kernel/panic.c b/kernel/panic.c
index 04e91ff..a507637 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -60,6 +60,28 @@ void __weak panic_smp_self_stop(void)
cpu_relax();
}
+/*
+ * Stop other cpus in panic. Architecture code may override this to
+ * with more suitable version. Moreover, if the architecture supports
+ * crash dump, it should also save the states of stopped cpus.
+ *
+ * This function should be called only once.
+ */
+void __weak panic_smp_stop_cpus(void)
+{
+ static int cpus_stopped;
+
+ if (!cpus_stopped) {
+ /*
+ * Note smp_send_stop is the usual smp shutdown function,
+ * which unfortunately means it may not be hardened to
+ * work in a panic situation.
+ */
+ smp_send_stop();
+ cpus_stopped = 1;
+ }
+}
+
/**
* panic - halt the system
* @fmt: The text string to print
@@ -120,12 +142,7 @@ void panic(const char *fmt, ...)
if (!crash_kexec_post_notifiers)
crash_kexec(NULL);
- /*
- * Note smp_send_stop is the usual smp shutdown function, which
- * unfortunately means it may not be hardened to work in a panic
- * situation.
- */
- smp_send_stop();
+ panic_smp_stop_cpus();
/*
* Run any panic handlers, including those that might need to
--
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