Hi Michal,
On 9/17/26 3:44 PM, Michal Suchánek wrote:
Hello,
On Wed, Sep 16, 2026 at 11:41:38PM +0530, Shrikanth Hegde wrote:
Hi Michal,
It seems easy to re-create.
The key is running bcc/bpf program in parallel to kernel build.
For example, these two in parallal, leads to stack corruption panic.
Stacktrace does differ sometimes.
./funccount rcu* -d 100
make -j 32
Boom. Will try to debug this further.
A bit more debugging.
1. A few functions seems to crash, specially ones that call schedule.
So picked schedule itself for tracing
2. Used plain ftrace. No crash.
3. Used kprobes. Boom. Crash appears. But this helped to avoid BPF JIT, or BCC
part of it.
4. Did some preempt count validation with annotations. Seems to be holding fine.
5. Since unlock can call schedule while tracing schedule, there is possible
looping.
Need to see further why it happens to be crashing there. Maybe regs or paca
handling needs a closer look.
For now, below patch helps to keep the system stable under kprobes, bcc tools.
I will look further into see why exactly it is crashing and below one is going
to
be the proper fix or not.
Feel free to give it a try.
thanks for the patch.
While it is mangled by the e-mail client in different way compared to
the previous patch it does seem to mitigate the issue.
Thanks for trying.
As it is unlikely the board where KVM lockup was originally observed is
running kpbobes it will probably not address the original problem.
Give it a try.
I am suspecting both lockup, stack corruptions are secondary symptoms here.
While recreate, I have different type of traces.
Thanks
Michal
---
arch/powerpc/kernel/kprobes-ftrace.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/powerpc/kernel/kprobes-ftrace.c
b/arch/powerpc/kernel/kprobes-ftrace.c
index f8208c027148..bcb1e8a8995d 100644
--- a/arch/powerpc/kernel/kprobes-ftrace.c
+++ b/arch/powerpc/kernel/kprobes-ftrace.c
@@ -63,7 +63,9 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long
parent_nip,
__this_cpu_write(current_kprobe, NULL);
}
out:
+ preempt_disable_notrace();
ftrace_test_recursion_unlock(bit);
+ preempt_enable_no_resched_notrace();
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);
--
2.52.0
