Re: [PATCH v2 08/17] s390/pci: Remove races against pte updates

Niklas Schnelle
2020-10-12T14:41:41Z

... snip ...
>>> Cc: linux-media@vger.kernel.org
>>> Cc: Niklas Schnelle <schnelle@linux.ibm.com>
>>> Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
>>> Cc: linux-s390@vger.kernel.org
>>> --
>>> v2: Move VM_IO | VM_PFNMAP checks around so they keep returning EINVAL
>>> like before (Gerard)
>>
>> I think the above should go before the CC/Signed-off/Reviewev block.
>
> This is a per-subsystem bikeshed :-) drivers/gpu definitely wants it
> above, but most core subsystems want it below. I'll move it.

Today I learned, thanks! That said I think most of the time I've
actually not seen version change information in the commit message itself
only in the cover letters. I really don't care just looked odd to me.

>
>>> ---
>>> arch/s390/pci/pci_mmio.c | 98 +++++++++++++++++++++++-----------------
>>> 1 file changed, 57 insertions(+), 41 deletions(-)
>>>
>>> diff --git a/arch/s390/pci/pci_mmio.c b/arch/s390/pci/pci_mmio.c
>>> index 401cf670a243..1a6adbc68ee8 100644
>>> --- a/arch/s390/pci/pci_mmio.c
>>> +++ b/arch/s390/pci/pci_mmio.c
>>> @@ -119,33 +119,15 @@ static inline int __memcpy_toio_inuser(void __iomem *dst,
>>> return rc;
>>> }
>>>
>>> -static long get_pfn(unsigned long user_addr, unsigned long access,
>>> - unsigned long *pfn)
>>> -{
>>> - struct vm_area_struct *vma;
>>> - long ret;
>>> -
>>> - mmap_read_lock(current->mm);
>>> - ret = -EINVAL;
>>> - vma = find_vma(current->mm, user_addr);
>>> - if (!vma)
>>> - goto out;
>>> - ret = -EACCES;
>>> - if (!(vma->vm_flags & access))
>>> - goto out;
>>> - ret = follow_pfn(vma, user_addr, pfn);
>>> -out:
>>> - mmap_read_unlock(current->mm);
>>> - return ret;
>>> -}
>>> -
>>> SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr,
>>> const void __user *, user_buffer, size_t, length)
>>> {
>>> u8 local_buf[64];
>>> void __iomem *io_addr;
>>> void *buf;
>>> - unsigned long pfn;
>>> + struct vm_area_struct *vma;
>>> + pte_t *ptep;
>>> + spinlock_t *ptl;
>>
>> With checkpatch.pl --strict the above yields a complained
>> "CHECK: spinlock_t definition without comment" but I think
>> that's really okay since your commit description is very clear.
>> Same oin line 277.
>
> I think this is a falls positive, checkpatch doesn't realize that
> SYSCALL_DEFINE3 is a function, not a structure. And in a structure I'd
> have added the kerneldoc or comment.

Interesting, your theory sounds convincing, I too thought this
was a bit too pedantic.

>
> I'll fix up all the nits you've found for the next round. Thanks for
> taking a look.

You're welcome hope I didn't sound pedantic. I think you've a lot
more experience actually and this can indeed turn into bikeshedding
but since I was answering anyway and most of this was checkpatch…

> -Daniel
>