linux-kernel - Re: [PATCH] rcu: remove unnecessary check cpu_no_qs.norm on rcu_report_qs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAM7-yPTrHN1xPXWjSUrJeTEOuy78DpmL8ytUY+a4ZOekiAbnZg@mail.gmail.com>
Date:   Sat, 22 Jul 2023 21:14:28 +0100
From:   Yun Levi <ppbuk5246@...il.com>
To:     paulmck@...nel.org
Cc:     frederic@...nel.org, quic_neeraju@...cinc.com,
        joel@...lfernandes.org, osh@...htriplett.org, boqun.feng@...il.com,
        rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com, qiang.zhang1211@...il.com,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: remove unnecessary check cpu_no_qs.norm on rcu_report_qs_rdp

Hi Paul.

> Suppose that the scheduler-clock interrupt invoking rcu_sched_clock_irq()
> happened just before the lock was acquired in rcu_report_qs_rdp().
> Suppose further that the RCU grace-period kthread started a new grace
> period just before that interrupt occurred.  Then mightn't that interrupt
> notice the new grace period and set ->cpu_no_qs.b.norm to true before
> fully returning?

IIUC, RCU grace-period kthread couldn't start new grace period
because the interrupted cpu don't report qs to rnp  via rcu_report_qs_rdp.
That situation is listened like new gp could be started thou all cpus
doesn't enter yet.
That's is the reason why it's better to use WARN_ON_ONCE as you suggest
to notice if the buggy situation happens

Am I missing something or wrong?

Thanks.

--------
Sincerely,
Levi.