netdev - Re: [PATCH net v2] napi: fix race inside napi

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Message-ID: <20210923061417.049df44d@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 23 Sep 2021 06:14:17 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     netdev@...r.kernel.org, linyunsheng@...wei.com,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Neil Horman <nhorman@...hat.com>,
        Dust Li <dust.li@...ux.alibaba.com>,
        Wei Wang <weiwan@...gle.com>
Subject: Re: [PATCH net v2] napi: fix race inside napi_enable

On Wed, 22 Sep 2021 14:47:47 +0800 Xuan Zhuo wrote:
> > Why don't you just invert the order of clearing the bits:  
> 
> I think it should be an atomic operation. The original two-step clear itself is
> problematic. So from this perspective, it is not just a solution to this
> problem.

[resending, my MUA seems to have corrupted the CC list previously]

Can you show what breaks by it being non-atomic?

Because, again, the disable part is not atomic. Either it's needed on
both sides or it's not needed on either.