netdev - Re: [PATCH] r8169: Fix irq masking in rtl8169

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Message-ID: <20090319222302.GA1972@electric-eye.fr.zoreil.com>
Date:	Thu, 19 Mar 2009 23:23:02 +0100
From:	Francois Romieu <romieu@...zoreil.com>
To:	Karsten Wiese <fzu@...gehoertderstaat.de>
Cc:	netdev@...r.kernel.org, Rafael Wysocki <rjw@...k.pl>
Subject: Re: [PATCH] r8169: Fix irq masking in rtl8169_interrupt()

Karsten Wiese <fzu@...gehoertderstaat.de> :
[...]
> Found it: CONFIG_DEBUG_SHIRQ is set here causing a "test-call" to
> rtl8169_interrupt() from irq_request().
> 
> $SUBJECT patch is ok, me still thinks. You ?

I will have to convince myself that nothing bad can happen in the
window between netif_rx_schedule_prep and RTL_W16. No big deal.

I do not understand why / how the patch works at all : AFAIU, the status
register must contain some napi-related event in order for the patch to
make a difference. That's exactly what rtl8169_irq_mask_and_ack() is
supposed to prevent. -> Does it fail ?

So I'd really like to understand what is going on here.

PS: while I agree on the motivation for CONFIG_DEBUG_SHIRQ, I wonder if
it is 100% safe to run an IRQ handler from a context which does not
adhere to the original semantic. If its {disable/enable}_irq pair races
with a similar pair due to a different driver on the same (shared) irq,
things could imho be unsafe.

-- 
Ueimor
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