linux-kernel - Re: [PATCH 5.10 462/717] ice, xsk: clear the status bits for the next_to

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Message-ID: <20201228145105.4eb4a14f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 28 Dec 2020 14:51:05 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Björn Töpel 
        <bjorn.topel@...el.com>
Subject: Re: [PATCH 5.10 462/717] ice, xsk: clear the status bits for the
 next_to_use descriptor

On Mon, 28 Dec 2020 17:29:07 -0500 Sasha Levin wrote:
> On Mon, Dec 28, 2020 at 10:54:23AM -0800, Jakub Kicinski wrote:
> >On Mon, 28 Dec 2020 13:47:40 +0100 Greg Kroah-Hartman wrote:  
> >> From: Björn Töpel <bjorn.topel@...el.com>
> >>
> >> [ Upstream commit 8d14768a7972b92c73259f0c9c45b969d85e3a60 ]
> >>
> >> On the Rx side, the next_to_use index points to the next item in the
> >> HW ring to be refilled/allocated, and next_to_clean points to the next
> >> item to potentially be processed.
> >>
> >> When the HW Rx ring is fully refilled, i.e. no packets has been
> >> processed, the next_to_use will be next_to_clean - 1. When the ring is
> >> fully processed next_to_clean will be equal to next_to_use. The latter
> >> case is where a bug is triggered.
> >>
> >> If the next_to_use bits are not cleared, and the "fully processed"
> >> state is entered, a stale descriptor can be processed.
> >>
> >> The skb-path correctly clear the status bit for the next_to_use
> >> descriptor, but the AF_XDP zero-copy path did not do that.
> >>
> >> This change adds the status bits clearing of the next_to_use
> >> descriptor.
> >>
> >> Fixes: 2d4238f55697 ("ice: Add support for AF_XDP")
> >> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> >> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> >> Signed-off-by: Sasha Levin <sashal@...nel.org>  
> >
> >Oh wow, so much for Sasha waiting longer for code to get tested before
> >auto-pulling things into stable :/  
> 
> The timeline is usually for a commit to appear in a release, and it did.
> Was it too early?

Hm, I'm not sure of exact semantics but I meant a final release, 
not an -rc. 

Plus I thought the point of things being part of a release is that
people actually get a chance to test that release. -rc1 was cut 24
hours ago. I guess a "release" is used as a yardstick here, to 
measure time, not for practical reasons?

> >I have this change and other changes here queued, but haven't sent the
> >submission yet.  
> 
> What do you mean with "queued"? Its in Linus's tree for about two weeks
> now.

Networking maintainers have their own queue for patches that will go to
stable:

https://patchwork.kernel.org/bundle/netdev/stable/?state=*

> >How long is the auto-backporting delay in terms of calendar days?  
> 
> The autosel stuff is about 2-3(-4) weeks at this point, stuff with a
> fixes tag gets picked up in about 2 weeks.

$ git show 8d14768a7972b92c73259f0c9c45b969d85e3a60 --format='%cD' --no-patch
Wed, 16 Dec 2020 10:51:07 -0800
$ git show 8d14768a7972b92c73259f0c9c45b969d85e3a60 --format='%aD' --no-patch
Fri, 11 Dec 2020 15:57:11 +0100

Two weeks from author date. That's a little short because.. I also
delay things by up to two weeks :) so you'll grab patches which are
sitting in networking stable queue.

And all networking fixes should have a Fixes tag, so that's no
discriminator to be honest.