Re: p54usb kernel panic on recent mainline kernels

[Christian Lamparter <chunkeey@googlemail.com>]

Alright, here's lunch [for the people in CET].

On Saturday, December 27, 2014 11:10:16 AM Christian Lamparter wrote:
> On Saturday, December 27, 2014 12:15:58 AM Christopher Chavez wrote:
> > > My bisection led to a branch commit d17ec4d as the "bad" commit. 
> > > Rather than finding out where the bisection went bad, I added 
> > > code to check skb->tail, skb->end, and the length to be added.
> > > At the time of the call that panics, there are 6 bytes between
> > > tail and end with 8 bytes needed.
> > >
> > > I will be looking for the place where the driver calculates how
> > > large the skb should be.
> 
> From looking at a other patch from that time and context. I think: "
> 
> commit ca34e3b5c808385b175650605faa29e71e91991b
> Author: Ido Yariv <ido@wizery.com>
> Date:   Tue Jul 29 15:38:53 2014 +0300
> 
>     mac80211: Fix accounting of the tailroom-needed counter [1]
>     
> [...]
> I can think of several ways of dealing with this issue:
> 
>  2. add extra IEEE80211_KEY_FLAG_ or HW_FLAG to restore the old behavior.
>     This should be possible and relatively simple. But we/I have to be
>     especially careful to differentiate properly between the old and new.
>     [i.e.: I need to know what the deal is behind: 
>     IEEE80211_KEY_FLAG_GENERATE_IV_MGMT in this case? Looks like it can
>     be ignored?]
> 

---
[Note: for convenience this patch is rolled into one for now -
if it and the concept works, I'll make two parts. one for p54
one for mac80211 [both -stable]. It would be great if someone
could proofread the commit message though - and provide 
"tested-by" tags if possible]

mac80211: re-enable tailroom resizing when needed for hardware encryption

The patch "mac80211: Fix accounting of the tailroom-needed counter" reduced
the overhead associated with unnecessary resizing of outgoing frames. 
Unfortunately this change broke the assumption that there is always enough
tailroom and this in turn caused p54* to panic.   

Reported-by: Christopher Chavez <chrischavez@gmx.us>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
---
diff --git a/drivers/net/wireless/p54/main.c b/drivers/net/wireless/p54/main.c
index 97aeff0..b877c7f 100644
--- a/drivers/net/wireless/p54/main.c
+++ b/drivers/net/wireless/p54/main.c
@@ -751,6 +751,7 @@ struct ieee80211_hw *p54_init_common(size_t priv_data_len)
 		     IEEE80211_HW_SUPPORTS_PS |
 		     IEEE80211_HW_PS_NULLFUNC_STACK |
 		     IEEE80211_HW_MFP_CAPABLE |
+		     IEEE80211_HW_TAILROOM_CRYPTO |
 		     IEEE80211_HW_REPORTS_TX_ACK_STATUS;
 
 	dev->wiphy->interface_modes = BIT(NL80211_IFTYPE_STATION) |
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 58d719d..c04ac04 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1270,8 +1270,11 @@ struct ieee80211_vif *wdev_to_ieee80211_vif(struct wireless_dev *wdev);
  *
  * @IEEE80211_KEY_FLAG_GENERATE_IV: This flag should be set by the
  *	driver to indicate that it requires IV generation for this
- *	particular key. Setting this flag does not necessarily mean that SKBs
- *	will have sufficient tailroom for ICV or MIC.
+ *	particular key. Setting this flag does not mean that SKBs will
+ *	have sufficient tailroom for ICV or MIC. If additional tailroom
+ *	tailroom needs to be reserved for the ICV or MIC, the driver
+ *	should also set the hardware feature flag:
+ *      %IEEE80211_HW_TAILROOM_CRYPTO.
  * @IEEE80211_KEY_FLAG_GENERATE_MMIC: This flag should be set by
  *	the driver for a TKIP key if it requires Michael MIC
  *	generation in software.
@@ -1583,6 +1586,10 @@ struct ieee80211_tx_control {
  * @IEEE80211_HW_MFP_CAPABLE:
  *	Hardware supports management frame protection (MFP, IEEE 802.11w).
  *
+ * @IEEE80211_HW_TAILROOM_CRYPTO: The driver would like to have sufficient
+ *	tailroom for ICV or MIC for outgoing frames in order to perform
+ *	hardware encryption without any additional resizing overhead.
+ *
  * @IEEE80211_HW_SUPPORTS_UAPSD:
  *	Hardware supports Unscheduled Automatic Power Save Delivery
  *	(U-APSD) in managed mode. The mode is configured with
@@ -1673,7 +1680,7 @@ enum ieee80211_hw_flags {
 	IEEE80211_HW_MFP_CAPABLE			= 1<<13,
 	IEEE80211_HW_WANT_MONITOR_VIF			= 1<<14,
 	IEEE80211_HW_NO_AUTO_VIF			= 1<<15,
-	/* free slot */
+	IEEE80211_HW_TAILROOM_CRYPTO			= 1<<16,
 	IEEE80211_HW_SUPPORTS_UAPSD			= 1<<17,
 	IEEE80211_HW_REPORTS_TX_ACK_STATUS		= 1<<18,
 	IEEE80211_HW_CONNECTION_MONITOR			= 1<<19,
diff --git a/net/mac80211/key.c b/net/mac80211/key.c
index 0bb7038..c3e9a9a 100644
--- a/net/mac80211/key.c
+++ b/net/mac80211/key.c
@@ -140,7 +140,8 @@ static int ieee80211_key_enable_hw_accel(struct ieee80211_key *key)
 	if (!ret) {
 		key->flags |= KEY_FLAG_UPLOADED_TO_HARDWARE;
 
-		if (!(key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_MMIC))
+		if (!((key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_MMIC) ||
+		      (key->local->hw.flags & IEEE80211_HW_TAILROOM_CRYPTO)))
 			sdata->crypto_tx_tailroom_needed_cnt--;
 
 		WARN_ON((key->conf.flags & IEEE80211_KEY_FLAG_PUT_IV_SPACE) &&
@@ -188,7 +189,8 @@ static void ieee80211_key_disable_hw_accel(struct ieee80211_key *key)
 	sta = key->sta;
 	sdata = key->sdata;
 
-	if (!(key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_MMIC))
+	if (!((key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_MMIC) ||
+	      (key->local->hw.flags & IEEE80211_HW_TAILROOM_CRYPTO)))
 		increment_tailroom_need_count(sdata);
 
 	ret = drv_set_key(key->local, DISABLE_KEY, sdata,
@@ -884,7 +886,8 @@ void ieee80211_remove_key(struct ieee80211_key_conf *keyconf)
 	if (key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE) {
 		key->flags &= ~KEY_FLAG_UPLOADED_TO_HARDWARE;
 
-		if (!(key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_MMIC))
+		if (!((key->conf.flags & IEEE80211_KEY_FLAG_GENERATE_MMIC) ||
+		      (key->local->hw.flags & IEEE80211_HW_TAILROOM_CRYPTO)))
 			increment_tailroom_need_count(key->sdata);
 	}