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

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Message-ID: <20250104000035.1356-1-hdanton@sina.com>
Date: Sat,  4 Jan 2025 08:00:33 +0800
From: Hillf Danton <hdanton@...a.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc: syzbot <syzbot+882589c97d51a9de68eb@...kaller.appspotmail.com>,
	Vladimir Oltean <vladimir.oltean@....com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	lorenzo.stoakes@...cle.com,
	netdev@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] INFO: rcu detected stall in mas_preallocate (2)

On Fri, 3 Jan 2025 10:20:34 -0500 "Liam R. Howlett" <Liam.Howlett@...cle.com>
> * 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.
> 
In case you missed it, take a look at
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fb66df20a720

> 
> 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