[PATCH 23/24] powerpc/mm: Cleanup check for stack expansion
mpe at ellerman.id.au
Tue Jul 25 21:19:47 AEST 2017
LEROY Christophe <christophe.leroy at c-s.fr> writes:
> Michael Ellerman <mpe at ellerman.id.au> a écrit :
>> LEROY Christophe <christophe.leroy at c-s.fr> writes:
>>> Benjamin Herrenschmidt <benh at kernel.crashing.org> a écrit :
>>>> When hitting below a VM_GROWSDOWN vma (typically growing the stack),
>>>> we check whether it's a valid stack-growing instruction and we
>>>> check the distance to GPR1. This is largely open coded with lots
>>>> of comments, so move it out to a helper.
>>> Did you have a look at the following patch ? It's been waiting for
>>> application for some weeks now.
>> I actually merged it last merge window, but found I had no good way to
>> test it, so I took it out again until I can write a test case for it.
>> The way I realised it wasn't being tested was by removing all the
>> store_updates_sp logic entirely and having my system run happily for
>> several days :}
> Which demonstrates how unlikely this is, hence doing that get_user()
> at every fault is waste of time.
Yes I agree.
> How do you plan to handle that in parralele to ben's serie ?
Not sure :)
> I'll be back from vacation next week and may help finding a way to
> test that. (A test program using alloca() ?)
I was thinking hand-crafted asm, but that might be a pain to get working
for 32 & 64-bit, in which case alloca() might work.
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