netdev - Re: [PATCH net v1] lan743x: prevent entire kernel HANG on open, for some platforms

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Message-ID: <20201114152819.6b89d74a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sat, 14 Nov 2020 15:28:19 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Sven Van Asbroeck <thesven73@...il.com>
Cc:     Bryan Whitehead <bryan.whitehead@...rochip.com>,
        David S Miller <davem@...emloft.net>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v1] lan743x: prevent entire kernel HANG on open, for
 some platforms

On Thu, 12 Nov 2020 15:47:41 -0500 Sven Van Asbroeck wrote:
> From: Sven Van Asbroeck <thesven73@...il.com>
> 
> On arm imx6, when opening the chip's netdev, the whole Linux
> kernel intermittently hangs/freezes.
> 
> This is caused by a bug in the driver code which tests if pcie
> interrupts are working correctly, using the software interrupt:
> 
> 1. open: enable the software interrupt
> 2. open: tell the chip to assert the software interrupt
> 3. open: wait for flag
> 4. ISR: acknowledge s/w interrupt, set flag
> 5. open: notice flag, disable the s/w interrupt, continue
> 
> Unfortunately the ISR only acknowledges the s/w interrupt, but
> does not disable it. This will re-trigger the ISR in a tight
> loop.
> 
> On some (lucky) platforms, open proceeds to disable the s/w
> interrupt even while the ISR is 'spinning'. On arm imx6,
> the spinning ISR does not allow open to proceed, resulting
> in a hung Linux kernel.
> 
> Fix minimally by disabling the s/w interrupt in the ISR, which
> will prevent it from spinning. This won't break anything because
> the s/w interrupt is used as a one-shot interrupt.
> 
> Note that this is a minimal fix, overlooking many possible
> cleanups, e.g.:
> - lan743x_intr_software_isr() is completely redundant and reads
>   INT_STS twice for no apparent reason
> - disabling the s/w interrupt in lan743x_intr_test_isr() is now
>   redundant, but harmless
> - waiting on software_isr_flag can be converted from a sleeping
>   poll loop to wait_event_timeout()
> 
> Fixes: 23f0703c125b ("lan743x: Add main source files for new lan743x driver")
> Tested-by: Sven Van Asbroeck <thesven73@...il.com> # arm imx6 lan7430
> Signed-off-by: Sven Van Asbroeck <thesven73@...il.com>

Applied, thank you!