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Date:	Thu, 26 Jun 2008 02:16:58 -0700 (PDT)
From:	David Miller <>
Subject: Re: [PATCH] igb: completely disable interrupts during netpoll

From: "Brandeburg, Jesse" <>
Date: Thu, 26 Jun 2008 00:23:59 -0700

> I think the deadlocks occur (only when using netpoll) because the tx
> cleanup (igb_clean_tx_irq) is being called simultaneously from two
> routines, which generally is guaranteed not to happen in regular
> everyday napi mode because of the bh_disable before calling dev->poll.

Thanks for the info, it's clear what the IGB driver bug is.

It's that the TX reclaim is not happening in the ->poll() handler.  If
you did that, all of this would work out correctly and you wouldn't
need to disable the IRQ with disable_irq() to prevent deadlocks.

Instead IGB what does is do TX reclaim inside of it's hw interrupt

And that is actually making much more work than if you did it properly
from a NAPI ->poll() context.  When igb_unmap_and_free_tx_resource()
runs from the HW interrupt it is going to queue these packet frees up
into the mid-layer's per-cpu TX free queue, and that will schedule yet
another software interrupt to actually run the kfree_skb()'s on all of
these liberated TX frames.

I moved the napi context out of the generic net device, use it! :-)
And then you can call dev_kfree_skb() directly from
igb_unmap_and_free_tx_resource() instead of dev_kfree_skb_any().
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