Messages in this thread | | | Subject | Re: [PATCH V7] mm/debug: Add tests validating architecture page table helpers | From | Anshuman Khandual <> | Date | Fri, 25 Oct 2019 15:40:36 +0530 |
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On 10/25/2019 02:22 PM, Christophe Leroy wrote: > > > Le 25/10/2019 à 10:24, Anshuman Khandual a écrit : >> >> >> On 10/25/2019 12:41 PM, Christophe Leroy wrote: >>> >>> >>> Le 25/10/2019 à 07:52, Qian Cai a écrit : >>>> >>>> >>>>> On Oct 24, 2019, at 11:45 PM, Anshuman Khandual <Anshuman.Khandual@arm.com> wrote: >>>>> >>>>> Nothing specific. But just tested this with x86 defconfig with relevant configs >>>>> which are required for this test. Not sure if it involved W=1. >>>> >>>> No, it will not. It needs to run like, >>>> >>>> make W=1 -j 64 2>/tmp/warns >>>> >>> >>> Are we talking about this peace of code ? >>> >>> +static unsigned long __init get_random_vaddr(void) >>> +{ >>> + unsigned long random_vaddr, random_pages, total_user_pages; >>> + >>> + total_user_pages = (TASK_SIZE - FIRST_USER_ADDRESS) / PAGE_SIZE; >>> + >>> + random_pages = get_random_long() % total_user_pages; >>> + random_vaddr = FIRST_USER_ADDRESS + random_pages * PAGE_SIZE; >>> + >>> + WARN_ON((random_vaddr > TASK_SIZE) || >>> + (random_vaddr < FIRST_USER_ADDRESS)); >>> + return random_vaddr; >>> +} >>> + >>> >>> ramdom_vaddr is unsigned, >>> random_pages is unsigned and lower than total_user_pages >>> >>> So the max value random_vaddr can get is FIRST_USER_ADDRESS + ((TASK_SIZE - FIRST_USER_ADDRESS - 1) / PAGE_SIZE) * PAGE_SIZE = TASK_SIZE - 1 >>> And the min value random_vaddr can get is FIRST_USER_ADDRESS (that's when random_pages = 0) >> >> That's right. >> >>> >>> So the WARN_ON() is just unneeded, isn't it ? >> >> It is just a sanity check on possible vaddr values before it's corresponding >> page table mappings could be created. If it's worth to drop this in favor of >> avoiding these unwanted warning messages on x86, will go ahead with it as it >> is not super important. >> > > But you are checking what ? That the compiler does calculation correctly or what ?
IIRC, probably this was for later if and when the vaddr calculation becomes dependent on other factors rather than this simple arithmetic involving start and end of process address space on a platform.
> As mentionned just above, based on the calculation done, what you are testing cannot happen, so I'm having a hard time understanding what kind of sanity check it can be.
You are right.
> > Can you give an exemple of a situation which could trigger the warning ?
I was mistaken. We dont need those checks for now, hence will drop them next time.
> > Christophe >
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