cvs commit: src/sys/kern kern_sig.c

[Scott Long]

David Xu wrote:
> Julian Elischer wrote:
> 
>>>
>>>
>>>>> The alternative, of course, is to just fix the code that assumes
>>>>> that swapping doesn't exist.
>>>>>
>>>>>     
>>>>
>>>>
>>>> First find all code written in such way, but it is not that easy.
>>>>   
>>>
>>>
>>>
>>> True.  If we changed msleep() to disable swapping by default, then
>>> we wouldn't have to worry about correctness problems related to
>>> missing some.
>>>  
>>>
>>
>> adding the flag to ENABLE swapping would be ABI compatible.
>>
>>
> how about adding a PNOSWAP to msleep ?  but I won't trust the kernel
> under swapping, because they can not give me 100% guarantee, my
> machine crashes several times per-month, even when fscking at boot time,
> mostly it is a page fault.
> 
> David Xu
> 
> 
> 
> 
> 

An msleep/tsleep option doesn't solve the problem because the the msleep
might happen several layers down from where the stack abuse is taking
place, and thus the caller would have no idea that it's needed.  The fix
for sigwait() is easy and can be applied without hacking in new options
that have limited value.  I don't argue that similar problems might
exist elsewhere, but swappable kstacks have been part of BSD since
before most of us knew where the power switch was on our Ataris, so it's
likely not to be a wide-spread and fundamental problem in the code.  I'd
be in favor of adding diagnostics that help catch these problems and
report them, but just throwing away kstack swapping in leiu of taking
the 2 minutes to fix sigwait() is pretty silly.

Scott