In panic path, fadump is triggered via a panic notifier function.
Before calling panic notifier functions, smp_send_stop() gets called,
which stops all CPUs except the panic'ing CPU. Commit 8389b37dffdc
("powerpc: stop_this_cpu: remove the cpu from the online map.") and
again commit bab26238bbd4 ("powerpc: Offline CPU in stop_this_cpu()")
started marking CPUs as offline while stopping them. So, if a kernel
has either of the above commits, vmcore captured with fadump via panic
path would show only the panic'ing CPU as online. Sample output of
crash-utility with such vmcore:
# crash vmlinux vmcore
...
KERNEL: vmlinux
DUMPFILE: vmcore [PARTIAL DUMP]
CPUS: 1
DATE: Wed Nov 10 09:56:34 EST 2021
UPTIME: 00:00:42
LOAD AVERAGE: 2.27, 0.69, 0.24
TASKS: 183
NODENAME: XXXXXXXXX
RELEASE: 5.15.0+
VERSION: #974 SMP Wed Nov 10 04:18:19 CST 2021
MACHINE: ppc64le (2500 Mhz)
MEMORY: 8 GB
PANIC: "Kernel panic - not syncing: sysrq triggered crash"
PID: 3394
COMMAND: "bash"
TASK: c0000000150a5f80 [THREAD_INFO: c0000000150a5f80]
CPU: 1
STATE: TASK_RUNNING (PANIC)
crash> p -x __cpu_online_mask
__cpu_online_mask = $1 = {
bits = {0x2, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}
}
crash>
crash>
crash> p -x __cpu_active_mask
__cpu_active_mask = $2 = {
bits = {0xff, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}
}
crash>
While this has been the case since fadump was introduced, the issue
was not identified for two probable reasons:
- In general, the bulk of the vmcores analyzed were from crash
due to exception.
- The above did change since commit 8341f2f222d7 ("sysrq: Use
panic() to force a crash") started using panic() instead of
deferencing NULL pointer to force a kernel crash. But then
commit de6e5d38417e ("powerpc: smp_send_stop do not offline
stopped CPUs") stopped marking CPUs as offline till kernel
commit bab26238bbd4 ("powerpc: Offline CPU in stop_this_cpu()")
reverted that change.
To avoid vmcore from showing only one CPU as online in panic path,
skip marking non panic'ing CPUs as offline while stopping them
during fadump crash.
Signed-off-by: Hari Bathini <hbath...@linux.ibm.com>
---
arch/powerpc/kernel/smp.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index c23ee842c4c3..20555d5d5966 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -61,6 +61,7 @@
#include <asm/cpu_has_feature.h>
#include <asm/ftrace.h>
#include <asm/kup.h>
+#include <asm/fadump.h>
#ifdef DEBUG
#include <asm/udbg.h>
@@ -626,7 +627,8 @@ static void nmi_stop_this_cpu(struct pt_regs *regs)
/*
* IRQs are already hard disabled by the smp_handle_nmi_ipi.
*/
- set_cpu_online(smp_processor_id(), false);
+ if (!(oops_in_progress && should_fadump_crash()))
+ set_cpu_online(smp_processor_id(), false);
spin_begin();
while (1)
@@ -650,7 +652,8 @@ static void stop_this_cpu(void *dummy)
* to know other CPUs are offline before it breaks locks to flush
* printk buffers, in case we panic()ed while holding the lock.
*/
- set_cpu_online(smp_processor_id(), false);
+ if (!(oops_in_progress && should_fadump_crash()))
+ set_cpu_online(smp_processor_id(), false);
spin_begin();
while (1)
--
2.31.1
