From: Hari Bathini hbathini@linux.ibm.com
[ 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@linux.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20211207103719.91117-2-hbathini@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 b7ceb041743c9..60f5fc14aa235 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 7201fdcf02f1c..c338f9d8ab37a 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> @@ -638,6 +639,15 @@ 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;