linux-kernel - Re: [PATCH 4.19 65/79] net: aquantia: fix out of memory condition on rx side

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Message-ID: <20190920112051.GA7865@amd>
Date:   Fri, 20 Sep 2019 13:20:51 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Igor Russkikh <igor.russkikh@...antia.com>,
        Dmitry Bogdanov <dmitry.bogdanov@...antia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 65/79] net: aquantia: fix out of memory condition on
 rx side

Hi!

> [ Upstream commit be6cef69ba570ebb327eba1ef6438f7af49aaf86 ]
> 
> On embedded environments with hard memory limits it is a normal although
> rare case when skb can't be allocated on rx part under high traffic.
> 
> In such OOM cases napi_complete_done() was not called.
> So the napi object became in an invalid state like it is "scheduled".
> Kernel do not re-schedules the poll of that napi object.
> 
> Consequently, kernel can not remove that object the system hangs on
> `ifconfig down` waiting for a poll.
> 
> We are fixing this by gracefully closing napi poll routine with correct
> invocation of napi_complete_done.
> 
> This was reproduced with artificially failing the allocation of skb to
> simulate an "out of memory" error case and check that traffic does
> not get stuck.


> --- a/drivers/net/ethernet/aquantia/atlantic/aq_vec.c
> +++ b/drivers/net/ethernet/aquantia/atlantic/aq_vec.c
> @@ -89,6 +89,7 @@ static int aq_vec_poll(struct napi_struct *napi, int budget)
>  			}
>  		}
>  
> +err_exit:
>  		if (!was_tx_cleaned)
>  			work_done = budget;
>  

This results in some... really "interesting" code that could use some
refactoring.

First, "goto err_exit" is now same as break.

Second, if (!self) now sets variable that is never used. "if (!self)
return 0;" would be more readable and would allow for less confusing
indentation.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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