On Fri, Nov 23, 2007 at 08:57:57PM +0300, Evgeniy Polyakov wrote: > On Fri, Nov 23, 2007 at 11:07:56AM -0600, Matt Mackall ([EMAIL PROTECTED]) > wrote: > > On Fri, Nov 23, 2007 at 01:55:19PM +0300, Evgeniy Polyakov wrote: > > > On Fri, Nov 23, 2007 at 12:21:57AM -0800, Andrew Morton ([EMAIL > > > PROTECTED]) wrote: > > > > > [2059664.615816] __iptables__: init4 IN=ppp0 OUT=ppp0 WARNING: at > > > > > kernel/softirq.c:139 local_bh_enable() > > > > > [2059664.620535] [<80120364>] local_bh_enable+0x3c/0x97 > > > > > > > > [2059664.620657] [<8011c205>] __call_console_drivers+0x61/0x6d > > > > > [2059664.620669] [<8011c3fc>] release_console_sem+0x164/0x1bf > > > > > [2059664.620679] [<8011c81f>] vprintk+0x27a/0x2ff > > > > > > > If that trace is to be beieved we're doing nefilter stuff on packets > > > > which > > > > were sent across netconsole. > > > > > > > > This probably isn't anything the netfilter guys have thought about. And > > > > probably we don't want them to. Is there some simple way in which we > > > > can > > > > exempt netconsole from netfilter processing? > > > > > > This is not about netfilter, but about freeing skb in interrupt context, > > > which is not allowed, and in interrupt skbs are queued to be freed in > > > softirq, > > > but netcnsole wants to flush softirq freeing queue. That is a question: > > > why? > > > > My memory here is hazy, but I think this exists to rescue netconsole > > in low-memory situations. This bit originated with Ingo, so maybe he > > can recall. > > > > Netpoll can process an arbitrary number of skbs inside a single > > interrupt. Think sysrq-t at one packet per line or kgdboe where the > > entire trace session can happen inside one very long interrupt. > > > > Perhaps we can refine this to mark netpoll's skbs (perhaps with > > ->destructor?) and delete only skbs we own. As these are never passed > > through any of the other route/xfrm/filter code, they should be safe > > to delete even in irq context, yes? > > > > > Removing zap_completion_queue() from find_skb() will fix the warning, > > > but I'm not sure this is a correct fix. I've added Matt to the Cc list. > > > > Care to try the sysrq-t or OOM message tests? > > We basically can not free skbs there - if it is interrupt context and > we are freeing some skb with destructor we will catch the warning anyway.
Perhaps I'm missing some context here. We don't free skbs with destructors in irq context in zap_completion_queue. We reinsert them on the completion list. We do this by calling dev_kfree_skb_any. So I'd be surprised if that was a problem. But I can imagine having problems for skbs without destructors which run into one of these in __kfree_skb: dst_release secpath_put nf_conntrack_put nf_conntrack_put_reasm nf_bridge_put ..some or all of which assume a softirq context. > No matter if we are under memory pressure or whatever - it is not > allowed - a lot of skbs are supposed to be freed in softirq context, > that is why dev_kfree_skb_any() exists. Some skbs we definitely -can- free in irq context. The only ones we care about are the ones generated by netpoll. If there's a reason you think netpoll's own skbs can't be freed, please describe it. > I think we can drop skbs _without_ destructor from the queue though in > that conditions given that we actually need only one. Huh? -- Mathematics is the supreme nostalgia of our time. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
