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Subject: Re: [patch 11/35] net: ionic: Replace in_interrupt() usage.
To:     Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>
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References: <20200927194846.045411263@linutronix.de>
 <20200927194920.918550822@linutronix.de>
From:   Shannon Nelson <snelson@pensando.io>
Message-ID: <5e4c3201-9d90-65b1-5c13-e2381445be1d@pensando.io>
Date:   Mon, 28 Sep 2020 10:24:47 -0700
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On 9/27/20 12:48 PM, Thomas Gleixner wrote:
> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>
> The in_interrupt() usage in this driver tries to figure out which context
> may sleep and which context may not sleep. in_interrupt() is not really
> suitable as it misses both preemption disabled and interrupt disabled
> invocations from task context.
>
> Conditionals like that in driver code are frowned upon in general because
> invocations of functions from invalid contexts might not be detected
> as the conditional papers over it.
>
> ionic_lif_addr() can be called from:
>
>   1) ->ndo_set_rx_mode() which is under netif_addr_lock_bh()) so it must not
>      sleep.
>
>   2) Init and setup functions which are in fully preemptible task context.
>
> _ionic_lif_rx_mode() has only one call path with BH disabled.
>
> ionic_link_status_check_request() has two call paths:
>
>   1) NAPI which obviously cannot sleep
>
>   2) Setup which is again fully preemptible task context
>
> Add 'can_sleep' arguments to the affected functions and let the callers
> provide the context instead of letting the functions deduce it.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Shannon Nelson <snelson@pensando.io>
> Cc: Pensando Drivers <drivers@pensando.io>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: netdev@vger.kernel.org

Acked-by: Shannon Nelson <snelson@pensando.io>

> ---
>
> While reviewing the callpaths, a couple of things were observed which could
> be improved:
>
> - ionic_lif_deferred_work() can iterate over the list. There is no need
>    to schedule the work item after each iteration

I think the original writer's intent was to avoid monopolizing the work 
thread for very long on any one cycle, with the thought that we'd be 
making more use of this than we currently are.  I'll address this.

>
> - ionic_link_status_check_request() could have ionic_deferred_work within
>    ionic_lif(). This would avoid memory allocation from NAPI. More
>    important, once IONIC_LIF_F_LINK_CHECK_REQUESTED is set and that alloc
>    fails, the link check never happens.

Thanks, I'll fix up that error condition.

>
> - ionic_lif_handle_fw_down() sets IONIC_LIF_F_FW_RESET. Invokes then
>    ionic_lif_deinit() which only invokes cancel_work_sync() if
>    IONIC_LIF_F_FW_RESET is not set. I think the logic is wrong here as
>    the work must always be cancled. Also the list with ionic_deferred
>    work items needs a clean up.

I'll look at that, thanks.

sln