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    DateTue, 18 Nov 2008 07:38:19 +0000
    FromJarek Poplawski <>
    SubjectRe: [PATCH] softirq: Use local_irq_save() in local_bh_enable()
    On Mon, Nov 17, 2008 at 05:16:17PM +0100, Ingo Molnar wrote:
    > 
    > * Jarek Poplawski <jarkao2@gmail.com> wrote:
    > 
    > > This report: http://marc.info/?l=linux-netdev&m=122599341430090&w=2 
    > > shows local_bh_enable() is used in the wrong context (irqs 
    > > disabled). It happens when a usual network receive path is called by 
    > > netconsole, which simply turns off irqs around this all. Probably 
    > > this is wrong, but it worked like this long time, and it's not 
    > > trivial to fix this.
    > > 
    > > Anyway, a commit 0f476b6d91a1395bda6464e653ce66ea9bea7167 "softirq: 
    > > remove irqs_disabled warning from local_bh_enable" can break things 
    > > after changing from local_irq_save() to local_irq_disable(). Before 
    > > this commit there was only a warning, now a lockup is possible, so 
    > > it could be treated as a regression. This patch reverts the change 
    > > in irqs.
    > 
    > hm, but calling local_bh_enable() with hardirqs off is a bug. It might 
    > be a long-standing bug, but it can cause lockups even with that change 
    > reverted: when we process softirqs in local_bh_enable().
    
    I think it's what they call a regression: this is a long-standing bug,
    and this commit doesn't fix this, but can cause additional lockups.
    
    > So why not 
    > fix the bug instead?
    
    It's not about instead: this bug could be fixed as well (if somebody
    knows how to do it "properly" without hacks like:
    	if (!in_irq())
    		local_bh_disable();
    etc.; but, I guess, the network code has more such bh disabling).
    Jarek P.
    
    
    
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