From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S271182AbTGWR4K (ORCPT ); Wed, 23 Jul 2003 13:56:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S271187AbTGWR4K (ORCPT ); Wed, 23 Jul 2003 13:56:10 -0400 Received: from tudela.mad.ttd.net ([194.179.1.233]:65418 "EHLO tudela.mad.ttd.net") by vger.kernel.org with ESMTP id S271182AbTGWRzm (ORCPT ); Wed, 23 Jul 2003 13:55:42 -0400 Date: Wed, 23 Jul 2003 20:10:46 +0200 (MEST) From: Javier Achirica To: Daniel Ritz cc: linux-kernel , linux-net Subject: Re: [PATCH 2.5] fixes for airo.c In-Reply-To: <200307231956.58656.daniel.ritz@gmx.ch> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 23 Jul 2003, Daniel Ritz wrote: > [shortening the cc: list a bit..] > > On Wed July 23 2003 12:26, Javier Achirica wrote: > > > > You cannot use down() in xmit, as it may be called in interrupt context. I > > know it slows things down, but that's the only way I figured out of > > handling a transmission while the card is processing a long command. > > hu? no. you can do a down() as xmit is never called from interrupt context. and > the dev->hard_start_xmit() calls are serialized with the dev->xmit_lock. the > serialization is broken by the schedule_work() thing. Ok, sure. But then, if you are in interrupt context, whet do you do with the packet? There's no problem with serialization, because if the packet gets scheduled with schedule_work(), the queue it's also stopped (before releasing the xmit_lock) so dev->hard_start_xmit() doesn't get called again. > > > > I thought about the fix and I think it's fixed. The only case the race > > could happen is if there's some work pending to be scheduled and the queue > > gets started again (by the interrupt handler), so airo_start_xmit > > overwrites the priv->xmit data. Now, because of the new flag, the > > interrupt handler won't wake the queue until the pending packet is > > sent to the card (or fails) so I don't see how can the race happen > > (although I didn't see it until you pointed out :-( > > > > may be the flag fixes the problem, but it adds complexity... I know. It's the best I could do. Anyway, in the works there's a complete rewrite of the packet handling, moving from I/O port access to mapped memory. I'll get into that once I get this version stable and the other one working. Javier Achirica > > > > On Wed, 23 Jul 2003, Daniel Ritz wrote: > > > > > ok, now the braindamaged thing called sourceforge showed the changes, but: > > > - i don't think the race is fixed. just remove the whole down_trylock() > > > crap in the xmit altogether and replace it with a single down(). faster, > > > simpler, not racy...and with the schedule_work you win nothing, you lose > > > speed > > > - please don't commit bugfixes and new features in the same changeset... > > > - the loop-forever fix in transmit_allocate: you should have copied the > > > comment > > > changes from my patch too, so the spin-forever-comment goes away... > > > > > > i look closer when i'm home, having a real operating system to work on, not > > > this > > > winblows box at work now.. > > > > > > -daniel > > > > > > > > > Javier Achirica wrote: > > > > > > > > Today I updated the CVS and Sourceforge (airo-linux.sf.net) with the > > > > latest version (1.53) that (I hope) fixes the race problem. If everything > > > > is fine, I'll commit the changes to the kernel tree. > > > > > > > > Javier Achirica > > > > > > > > On Mon, 21 Jul 2003, Daniel Ritz wrote: > > > > > > > > > On Mon July 21 2003 21:44, Javier Achirica wrote: > > > > > > > > > > > > On Mon, 21 Jul 2003, Daniel Ritz wrote: > > > > > > > > > > > > > On Mon July 21 2003 13:00, Javier Achirica wrote: > > > > > > > > > > > > > > > > Daniel, > > > > > > > > > > > > > > > > Thank you for your patch. Some comments about it: > > > > > > > > > > > > > > > > - I'd rather fix whatever is broken in the current code than going > > > back to > > > > > > > > spinlocks, as they increase latency and reduce concurrency. In any > > > case, > > > > > > > > please check your code. I've seen a spinlock in the interrupt > > > handler that > > > > > > > > may lock the system. > > > > > > > > > > > > > > but we need to protect from interrupts while accessing the card and > > > waiting for > > > > > > > completion. semaphores don't protect you from that. > > > spin_lock_irqsave does. the > > > > > > > spin_lock in the interrupt handler is there to protect from > > > interrupts from > > > > > > > other processors in a SMP system (see Documentation/spinlocks.txt) > > > and is btw. > > > > > > > a no-op on UP. and semaphores are quite heavy.... > > > > > > > > > > > > Not really. You can still read the received packets from the card (as > > > > > > you're not issuing any command and are using the other BAP) while a > > > > > > command is in progress. There are some specific cases in which you > > > need > > > > > > to have protection, and that cases are avoided with the down_trylock. > > > > > > > > > > > > > > > > ok, i think i have to look closer...if the card can handle that then we > > > don't need > > > > > to irq-protect all the areas i did protect...but i do think that those > > > down_trylock and > > > > > then the schedule_work should be replaced by a simple > > > spinlock_irq_save... > > > > > > > > > > i look closer at it tomorrow. > > > > > you happen to have the tech spec lying aroung? > > > > > > > > > > > AFAIK, interrupt serialization is assured by the interrupt handler, so > > > you > > > > > > don't need to do that. > > > > > > > > > > > > > > - The fix for the transmit code you mention, is about fixing the > > > returned > > > > > > > > value in case of error? If not, please explain it to me as I don't > > > see any > > > > > > > > other changes. > > > > > > > > > > > > > > fixes: > > > > > > > - return values > > > > > > > - when to free the skb, when not > > > > > > > - disabling the queues > > > > > > > - netif_wake_queue called from the interrupt handler only (and on > > > the right > > > > > > > net_device) > > > > > > > - i think the priv->xmit stuff and then the schedule_work is evil: > > > > > > > if you return 0 from the dev->hard_start_xmit then the network > > > layer assumes > > > > > > > that the packet was kfree_skb()'ed (which does only frees the > > > packet when the > > > > > > > refcount drops to zero.) this is the cause for the keventd > > > killing, for sure! > > > > > > > > > > > > > > if you return 0 you already kfree_skb()'ed the packet. and that's > > > it. > > > > > > > > > > > > This is where I have the biggest problems. As I've read in > > > > > > Documentation/networking/driver.txt, looks like the packet needs to be > > > > > > freed "soon", but doesn't require to be before returning 0 in > > > > > > hard_start_xmit. Did I get it wrong? > > > > > > > > > > > > > > > > no, i got it wrong. but still...it's the xmit where the oops comes > > > from.... > > > > > > > > > > wait. isn't there a race in airo_do_xmit? at high xfer rates (when it > > > oopses) the > > > > > queue can wake right after it is stopped in the down_trylock section. so > > > you can > > > > > happen to loose an skb 'cos the write to priv->xmit is not protected at > > > all and > > > > > there should be a check so that only one skb can be queue there. no? > > > > > (and then the irq-handler can wake the queue too) > > > > > > > > > > ok, i think i got it now. i'll do a new patch tomorrow or so that tries: > > > > > - to fix the transmit not to oops > > > > > - to avoid disabling the irq's whenever possible > > > > > - using spinlocks instead of the heavier semaphores ('cos i think if > > > it's done cleaner > > > > > than i did it now, it's faster than the semas, and to make hch happy > > > :) > > > > > > > > > > > > > > > > Thanks for your help, > > > > > > Javier Achirica > > > > > > > > > > > > > > > > rgds > > > > > -daniel > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >