Re: [PATCH] perf: fix panic by disable ftrace on fault.c
From: Dave Hansen <hidden>
Date: 2021-09-13 14:55:19
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bpf, lkml
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.