From: Hari Bathini <hbathini@xxxxxxxxxxxxx>
[ Upstream commit 06e629c25daa519be620a8c17359ae8fc7a2e903 ]
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 not process register data for all CPUs except the panic'ing
CPU. 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 ensure post processing register data of all other CPUs happens
as intended, let panic() function take the crash friendly path (read
crash_smp_send_stop()) with the help of crash_kexec_post_notifiers
option. Also, as register data for all CPUs is captured by f/w, skip
IPI callbacks here for fadump, to avoid any complications in finding
the right backtraces.
Signed-off-by: Hari Bathini <hbathini@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20211207103719.91117-2-hbathini@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/powerpc/kernel/fadump.c | 8 ++++++++
arch/powerpc/kernel/smp.c | 10 ++++++++++
2 files changed, 18 insertions(+)
diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
index eddf362caedce..c3bb800dc4352 100644
--- a/arch/powerpc/kernel/fadump.c
+++ b/arch/powerpc/kernel/fadump.c
@@ -1641,6 +1641,14 @@ int __init setup_fadump(void)
else if (fw_dump.reserve_dump_area_size)
fw_dump.ops->fadump_init_mem_struct(&fw_dump);
+ /*
+ * In case of panic, fadump is triggered via ppc_panic_event()
+ * panic notifier. Setting crash_kexec_post_notifiers to 'true'
+ * lets panic() function take crash friendly path before panic
+ * notifiers are invoked.
+ */
+ crash_kexec_post_notifiers = true;
+
return 1;
}
subsys_initcall(setup_fadump);
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index d993f28107afa..cf99f57aed822 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -60,6 +60,7 @@
#include <asm/cpu_has_feature.h>
#include <asm/ftrace.h>
#include <asm/kup.h>
+#include <asm/fadump.h>
#ifdef DEBUG
#include <asm/udbg.h>
@@ -612,6 +613,15 @@ void crash_smp_send_stop(void)
{
static bool stopped = false;
+ /*
+ * In case of fadump, register data for all CPUs is captured by f/w
+ * on ibm,os-term rtas call. Skip IPI callbacks to other CPUs before
+ * this rtas call to avoid tricky post processing of those CPUs'
+ * backtraces.
+ */
+ if (should_fadump_crash())
+ return;
+
if (stopped)
return;
--
2.34.1
