On 9/12/21 8:30 PM, 王贇 wrote:
> According to the trace we know the story is like this, the NMI
> triggered perf IRQ throttling and call perf_log_throttle(),
> which triggered the swevent overflow, and the overflow process
> do perf_callchain_user() which triggered a user PF, and the PF
> process triggered perf ftrace which finally lead into a suspected
> stack overflow.
>
> This patch disable ftrace on fault.c, which help to avoid the panic.
...
> +# Disable ftrace to avoid stack overflow.
> +CFLAGS_REMOVE_fault.o = $(CC_FLAGS_FTRACE)
Was this observed on a mainline kernel?
How reproducible is this?
I suspect we're going into do_user_addr_fault(), then falling in here:
> if (unlikely(faulthandler_disabled() || !mm)) {
> bad_area_nosemaphore(regs, error_code, address);
> return;
> }
Then something double faults in perf_swevent_get_recursion_context().
But, you snipped all of the register dump out so I can't quite see
what's going on and what might have caused *that* fault. But, in my
kernel perf_swevent_get_recursion_context+0x0/0x70 is:
mov $0x27d00,%rdx
which is rather unlikely to fault.
Either way, we don't want to keep ftrace out of fault.c. This patch is
just a hack, and doesn't really try to fix the underlying problem. This
situation *should* be handled today. There's code there to handle it.
Something else really funky is going on.
