linux-kernel - Re: Wireless regression (was 2.6.38-rc3: FUSE (sshfs) hangs under load)

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Message-ID: <4D4BEB99.4060202@openwrt.org>
Date:	Fri, 04 Feb 2011 13:05:45 +0100
From:	Felix Fietkau <nbd@...nwrt.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	Miklos Szeredi <miklos@...redi.hu>, linux-kernel@...r.kernel.org,
	linux-wireless@...r.kernel.org,
	"John W. Linville" <linville@...driver.com>
Subject: Re: Wireless regression (was 2.6.38-rc3: FUSE (sshfs) hangs under
 load)

On 2011-02-04 12:41 PM, Felix Fietkau wrote:
> On 2011-02-04 7:49 AM, Dmitry Torokhov wrote:
>> On Thu, Feb 03, 2011 at 11:41:15AM -0800, Dmitry Torokhov wrote:
>>> On Thu, Feb 03, 2011 at 12:13:24PM +0100, Miklos Szeredi wrote:
>>> > On Wed, 2 Feb 2011, Dmitry Torokhov wrote:
>>> > > On Wed, Feb 02, 2011 at 08:52:36AM -0800, Dmitry Torokhov wrote:
>>> > > > On Wed, Feb 02, 2011 at 12:52:36PM +0100, Miklos Szeredi wrote:
>>> > > > > On Tue, 1 Feb 2011, Dmitry Torokhov wrote:
>>> > > > > > Hi,
>>> > > > > > 
>>> > > > > > After installing 2.6.38-rc3 (plus a few input patches) sshfs started to
>>> > > > > > misbehave on me under load. It starts off fine but when I try to compile
>>> > > > > > a few modules against kernel sources residing on the other box the
>>> > > > > > processes go into 'D' state and just sit there doing nothing.
>>> > > > > 
>>> > > > > Can you please post a stack trace from SysRq-T?
>>> > > > > 
>>> > > > 
>> ...
>>> > > 
>>> > > OK, so here are the stack traces you requested. First one is snapshot of
>>> > > when compile got stuck, the 2nd one is when I interrupted make which
>>> > > caused gcc to go to 'D' state.
>>> > 
>>> > There doesn't appear anything abnormal there.
>>> > 
>>> > It's going into D state after it has received an interrupt and sent it
>>> > along to the userspace filesystem.  Then it will go into
>>> > uninterruptible sleep until the answer is received.
>>> > 
>>> > So the hang is because the answer to an open request is not being
>>> > received.  I can't tell where it got stuck, apparently not anywhere on
>>> > the local machine.
>>> > 
>>> > Can you please get a log from sshfs with "-odebug,sshfs_debug" and
>>> > redirect stderr to a file?  That might tell a bit more about the
>>> > situation.  Or it might not...
>>> 
>>> Hmm, it might be just the network itself, last night mutt in ssh session
>>> froze on me as well. I guess I'll just have to finish my bisect
>>> exercise.
>>> 
>> 
>> I finished bisecting and it turned out that the problematic commit
>> happened to be in wireless (I have iwl3945):
>> 
>> commit 4cd06a344db752f513437138953af191cbe9a691
>> Author: Felix Fietkau <nbd@...nwrt.org>
>> Date:   Sat Dec 18 19:30:49 2010 +0100
>> 
>>     mac80211: skip unnecessary pskb_expand_head calls
>> 
>>     If the skb is not cloned and we don't need any extra headroom, there
>>     is no point in reallocating the skb head.
>> 
>>     Signed-off-by: Felix Fietkau <nbd@...nwrt.org>
>>     Signed-off-by: John W. Linville <linville@...driver.com>
>> 
>> With this commit reverted from 2.6.38-rc3 I can not reproduce sshfs
>> getting stuck here.
> I really don't see how this commit could be causing these issues, and
> I'm not aware of any similar issues affecting other drivers.
Could you please try this patch to see if it fixes the issue as well?

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index ffc6749..3168eae 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1547,7 +1547,7 @@ static int ieee80211_skb_resize(struct ieee80211_local *local,
 		skb_orphan(skb);
 	}
 
-	if (skb_header_cloned(skb))
+	if (skb_cloned(skb))
 		I802_DEBUG_INC(local->tx_expand_skb_head_cloned);
 	else if (head_need || tail_need)
 		I802_DEBUG_INC(local->tx_expand_skb_head);
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