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

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Sun, Nov 18, 2012 at 12:06:40PM -0500, Josh Coombs wrote:
> Starting with 3.6.5 on a Marvell Kirkwood based GoFlex Net I began
> observing scheduler bugs when using a USB based RTL8712 WiFi NIC.
> These would eventually overwhelm systemd's logger under moderate
> network activity and crash the box.

Cool, yet another systemd feature :)  sysvinit was less hastle...

> [   53.173973] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
> [   54.191655] BUG: scheduling while atomic: crond/144/0x40000300
> [   54.197537] Modules linked in: rmd160 sha1_generic hmac
> blowfish_generic blowfish_common sr_mod cdrom fbcon bitblit softcursor
> font udlfb syscopyarea sysfillrect sysimgblt fb_sys_fops fb
> hid_generic snd_usb_audio snd_usbmidi_lib snd_hwdep mct_u232
> snd_rawmidi snd_seq_device snd_pcm snd_page_alloc usbhid usbserial
> snd_timer snd hid soundcore mv_cesa cryptodev(O) ipv6 autofs4
> [   54.231214] [<c000d020>] (unwind_backtrace+0x0/0xe0) from
> [<c03fd1d0>] (__schedule_bug+0x48/0x60)
> [   54.240171] [<c03fd1d0>] (__schedule_bug+0x48/0x60) from
> [<c0401258>] (__schedule+0x4c/0x4bc)
> [   54.248773] [<c0401258>] (__schedule+0x4c/0x4bc) from [<c003b470>]
> (__cond_resched+0x24/0x34)
> [   54.257365] [<c003b470>] (__cond_resched+0x24/0x34) from
> [<c040175c>] (_cond_resched+0x3c/0x44)
> [   54.266134] [<c040175c>] (_cond_resched+0x3c/0x44) from
> [<c0010288>] (do_alignment+0x29c/0x784)
> [   54.274895] [<c0010288>] (do_alignment+0x29c/0x784) from
> [<c00083d8>] (do_DataAbort+0x34/0x98)

This is actually a known problem... and I have a patch which resolves it
but I've lost track of where things are with that patch through being
distracted by modern platforms... that said, it does seem to be pointing
at a problem which can be sorted in the driver which makes it more
efficient on ARM hardware.

> 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?