On Fri, Nov 14, 2014 at 2:55 PM, Thomas Gleixner <t...@linutronix.de> wrote:
>
> This stale entry is not relevant here because the thing is stuck in
> generic_exec_single().
That wasn't really my argument. The fact that "do_flush_tlb_all()" was
left over on the stack frame implies that we're not doing the
range-flush, and if it was some odd bug with a negative range or
something like that (due to the fix in commit ce9ec37bddb6), I'd
expect the lockup to be due to a hung do_kernel_range_flush() or
something. But the range flushing never even happens.
> So from smp_call_function_many() we end up via
> smp_call_function_single() in generic_exec_single().
>
> So the only ways to get stuck there are:
>
> csd_lock(csd);
> and
> csd_lock_wait(csd);
Judging by the code disassembly, it's the "csd_lock_wait(csd)" at the
end. The disassembly looks like
29: f3 90 pause
2b:* f6 43 18 01 testb $0x1,0x18(%rbx) <-- trapping instruction
2f: 75 f8 jne 0x29
31: 31 c0 xor %eax,%eax
and that "xor %eax,%eax" seems to be part of the "return 0"
immediately afterwards.
But that's not entirely conclusive, it's just a strong hint.
It does sound like there might be some IPI issue. I just don't see
*any* changes in this area since 3.17. Some unrelated APIC change? I
don't see that either. As you noted, there are KVM changes, but
apparently that isn't involved either.
Linus
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