[Patch v1 1/1] RTL8712 alignment bug in 3.6.5 on ARM

[Josh Coombs]

With the _malloc() adjusted as suggested, I'm still not seeing
scheduler bugs tracing back to the rtl8172 driver.  I am however
seeing allocation errors occasionally now in cryptodev on my test
system, so all is still not right.  This behavior was not present in
3.6.4, I haven't seen it in the 3.7 release candidates, I'm going to
see if I can nail down the exact commit that introduced this issue
with git-bisect to see if there is something that was masking the
problem that's been removed, or something unexpected, etc.  I'll
report back once I have more info.

Josh C

On Sun, Nov 18, 2012 at 1:20 PM, Andrew Lunn <andrew at lunn.ch> wrote:
>> >> diff -ruN a/drivers/staging/rtl8712/rtl871x_sta_mgt.c
>> >> b/drivers/staging/rtl8712/rtl871x_sta_mgt.c
>> >> --- a/drivers/staging/rtl8712/rtl871x_sta_mgt.c 2012-11-05
>> >> 03:57:06.000000000 -0500
>> >> +++ b/drivers/staging/rtl8712/rtl871x_sta_mgt.c 2012-11-13
>> >> 12:54:28.000000000 -0500
>> >> @@ -55,8 +55,8 @@
>> >>     NUM_STA + 4);
>> >>   if (pstapriv->pallocated_stainfo_buf == NULL)
>> >>   return _FAIL;
>> >> - pstapriv->pstainfo_buf = pstapriv->pallocated_stainfo_buf + 4 -
>> >> - ((addr_t)(pstapriv->pallocated_stainfo_buf) & 3);
>> >> + pstapriv->pstainfo_buf = pstapriv->pallocated_stainfo_buf + 8 -
>> >> + ((addr_t)(pstapriv->pallocated_stainfo_buf) & 7);
>> >
>> > Are you sure this is safe?  Is the allocated buffer large enough for
>> > those additional 4 bytes of alignment you're adding?
>>
>> I'm not certain on that, I bumped the allocations at Andrew's
>> suggestion, but don't know enough to certify the changes as 100%
>> correct.
>
> Its not correct.
>
> The original code is:
>
>         pstapriv->pallocated_stainfo_buf = _malloc(sizeof(struct sta_info) *
>                                                    NUM_STA + 4);
>         if (pstapriv->pallocated_stainfo_buf == NULL)
>                 return _FAIL;
>         pstapriv->pstainfo_buf = pstapriv->pallocated_stainfo_buf + 4 -
>                 ((addr_t)(pstapriv->pallocated_stainfo_buf) & 3);
>
> The 4 in the _malloc() also needs increasing to 8.
>
>     Andrew