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From: Thomas Gleixner <tglx@linutronix.de>
To: Dmitry Vyukov <dvyukov@google.com>,
	"Paul E. McKenney" <paulmck@kernel.org>
Cc: syzbot <syzbot+3ae5eaae0809ee311e75@syzkaller.appspotmail.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	the arch/x86 maintainers <x86@kernel.org>
Subject: Re: WARNING: suspicious RCU usage in idtentry_exit
Date: Fri, 29 May 2020 10:51:25 +0200	[thread overview]
Message-ID: <87tuzzm8du.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <CACT4Y+bVPSZVkWJquu5gk11ymhirsFvVFYHkexjqgBkgga379w@mail.gmail.com>

Dmitry,

Dmitry Vyukov <dvyukov@google.com> writes:
> On Thu, May 28, 2020 at 10:48 PM Paul E. McKenney <paulmck@kernel.org> wrote:
>> On Thu, May 28, 2020 at 10:19:02PM +0200, Thomas Gleixner wrote:
>> OK, from the .config, another suggestion is to build the kernel
>> with CONFIG_RCU_EQS_DEBUG=y.  This still requires that this issue be
>> reproduced, but it might catch the problem earlier.
>
> How much does it slow down execution? If we enable it on syzbot, it
> will affect all fuzzing done by syzbot always.
> It can tolerate significant slowdown and it's far from a production
> kernel (it enables KASAN, KCOV, LOCKDEP and more). But I am still
> asking because some debugging features are built without performance
> in mind at all (like let's just drop a global lock in every
> kmalloc/free, which may be too much even for a standard debug build).

It's not worse than lockdep.

Thanks,

        tglx

  reply	other threads:[~2020-05-29  8:51 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-26  3:54 WARNING: suspicious RCU usage in idtentry_exit syzbot
2020-05-28 13:33 ` Thomas Gleixner
2020-05-28 16:11   ` Paul E. McKenney
2020-05-28 20:19     ` Thomas Gleixner
2020-05-28 20:48       ` Paul E. McKenney
2020-05-29  6:20         ` Dmitry Vyukov
2020-05-29  8:51           ` Thomas Gleixner [this message]
2020-05-29 14:05           ` Paul E. McKenney
2020-05-29 14:32             ` Dmitry Vyukov
2020-05-29 16:07               ` Paul E. McKenney
2020-07-31  9:23   ` [tip: core/rcu] lockdep: Complain only once about RCU in extended quiescent state tip-bot2 for Paul E. McKenney

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