netdev - Re: [syzbot] [mm?] INFO: rcu detected stall in mas

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Message-ID: <p5ych35cl5ofdzvoobk6uxu4s7f5h3joogy6wee2sq3g4m4mxb@py7tzqwueh74>
Date: Fri, 3 Jan 2025 10:20:34 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: syzbot <syzbot+882589c97d51a9de68eb@...kaller.appspotmail.com>
Cc: akpm@...ux-foundation.org, davem@...emloft.net, jannh@...gle.com,
        jhs@...atatu.com, jiri@...nulli.us, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, lorenzo.stoakes@...cle.com, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, vbabka@...e.cz,
        vinicius.gomes@...el.com, xiyou.wangcong@...il.com
Subject: Re: [syzbot] [mm?] INFO: rcu detected stall in mas_preallocate (2)

* syzbot <syzbot+882589c97d51a9de68eb@...kaller.appspotmail.com> [250102 19:47]:
> syzbot has bisected this issue to:
> 
> commit 5a781ccbd19e4664babcbe4b4ead7aa2b9283d22
> Author: Vinicius Costa Gomes <vinicius.gomes@...el.com>
> Date:   Sat Sep 29 00:59:43 2018 +0000
> 
>     tc: Add support for configuring the taprio scheduler
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=117df818580000
> start commit:   feffde684ac2 Merge tag 'for-6.13-rc1-tag' of git://git.ker..
> git tree:       upstream
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=137df818580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=157df818580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=50c7a61469ce77e7
> dashboard link: https://syzkaller.appspot.com/bug?extid=882589c97d51a9de68eb
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10e8a8df980000
> 
> Reported-by: syzbot+882589c97d51a9de68eb@...kaller.appspotmail.com
> Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio scheduler")
> 
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> 

This looks wrong, if this is a bug (which looks like it is since it has
a syzbot reproducer?), then it's different than the previous two reports
and probably not related.


Vinicius,

Looking at the patch, it seems you missed some users of -1 vs
TAPRIO_ALL_GATES_OPEN in taprio_peek().  The comment in taprio_dequeue()
is useful - maybe the gate_mask rcu lock/unlock could be a function and
have that comment live in a static inline function?

Thanks,
Liam