From: Peter Zijlstra <peterz@infradead.org>
To: Marco Elver <elver@google.com>
Cc: "Ahmed S. Darwish" <a.darwish@linutronix.de>,
mingo@kernel.org, will@kernel.org, tglx@linutronix.de,
x86@kernel.org, linux-kernel@vger.kernel.org,
rostedt@goodmis.org, bigeasy@linutronix.de, davem@davemloft.net,
sparclinux@vger.kernel.org, mpe@ellerman.id.au,
linuxppc-dev@lists.ozlabs.org, heiko.carstens@de.ibm.com,
linux-s390@vger.kernel.org, linux@armlinux.org.uk
Subject: Re: [PATCH v4 7/8] lockdep: Change hardirq{s_enabled,_context} to per-cpu variables
Date: Tue, 23 Jun 2020 20:12:32 +0200 [thread overview]
Message-ID: <20200623181232.GB4800@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200623175957.GA106514@elver.google.com>
On Tue, Jun 23, 2020 at 07:59:57PM +0200, Marco Elver wrote:
> On Tue, Jun 23, 2020 at 06:37PM +0200, Peter Zijlstra wrote:
> > On Tue, Jun 23, 2020 at 06:13:21PM +0200, Ahmed S. Darwish wrote:
> > > Well, freshly merged code is using it. For example, KCSAN:
> > >
> > > => f1bc96210c6a ("kcsan: Make KCSAN compatible with lockdep")
> > > => kernel/kcsan/report.c:
> > >
> > > void kcsan_report(...)
> > > {
> > > ...
> > > /*
> > > * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if
> > > * we do not turn off lockdep here; this could happen due to recursion
> > > * into lockdep via KCSAN if we detect a race in utilities used by
> > > * lockdep.
> > > */
> > > lockdep_off();
> > > ...
> > > }
> >
> > Marco, do you remember what exactly happened there? Because I'm about to
> > wreck that. That is, I'm going to make TRACE_IRQFLAGS ignore
> > lockdep_off().
>
> Yeah, I was trying to squash any kind of recursion:
>
> lockdep -> other libs ->
> -> KCSAN
> -> print report
> -> dump stack, printk and friends
> -> lockdep -> other libs
> -> KCSAN ...
>
> Some history:
>
> * Initial patch to fix:
> https://lore.kernel.org/lkml/20200115162512.70807-1-elver@google.com/
That patch is weird; just :=n on lockdep.c should've cured that, the
rest is massive overkill.
> * KCSAN+lockdep+ftrace:
> https://lore.kernel.org/lkml/20200214211035.209972-1-elver@google.com/
That doesn't really have anything useful..
> lockdep now has KCSAN_SANITIZE := n, but we still need to ensure that
> there are no paths out of lockdep, or the IRQ flags tracing code, that
> might lead through other libs, through KCSAN, libs used to generate a
> report, and back to lockdep.
>
> I never quite figured out the exact trace that led to corruption, but
> avoiding any kind of potential for recursion was the only thing that
> would avoid the check_flags() warnings.
Fair enough; I'll rip it all up and boot a KCSAN kernel, see what if
anything happens.
next prev parent reply other threads:[~2020-06-23 18:13 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-23 8:36 [PATCH v4 0/8] lockdep: Change IRQ state tracking to use per-cpu variables Peter Zijlstra
2020-06-23 8:36 ` [PATCH v4 1/8] lockdep: Prepare for NMI IRQ state tracking Peter Zijlstra
2020-07-11 10:09 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-06-23 8:36 ` [PATCH v4 2/8] x86/entry: Fix NMI vs " Peter Zijlstra
2020-07-11 10:09 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-06-23 8:36 ` [PATCH v4 3/8] sparc64: Fix asm/percpu.h build error Peter Zijlstra
2020-06-23 21:35 ` David Miller
2020-07-11 10:09 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-06-23 8:36 ` [PATCH v4 4/8] powerpc64: Break asm/percpu.h vs spinlock_types.h dependency Peter Zijlstra
2020-06-23 8:36 ` [PATCH v4 5/8] s390: Break cyclic percpu include Peter Zijlstra
2020-07-11 10:09 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-06-23 8:36 ` [PATCH v4 6/8] arm: " Peter Zijlstra
2020-06-23 9:02 ` Will Deacon
2020-06-24 17:53 ` Peter Zijlstra
2020-06-25 7:31 ` Will Deacon
2020-07-11 10:09 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-06-23 8:36 ` [PATCH v4 7/8] lockdep: Change hardirq{s_enabled,_context} to per-cpu variables Peter Zijlstra
2020-06-23 15:00 ` Ahmed S. Darwish
2020-06-23 15:24 ` Peter Zijlstra
2020-06-23 16:13 ` Ahmed S. Darwish
2020-06-23 16:37 ` Peter Zijlstra
2020-06-23 17:59 ` Marco Elver
2020-06-23 18:12 ` Peter Zijlstra [this message]
2020-06-23 18:39 ` Marco Elver
2020-06-23 19:13 ` Marco Elver
2020-06-23 19:41 ` Peter Zijlstra
2020-06-23 20:08 ` Peter Zijlstra
2020-06-23 20:24 ` Peter Zijlstra
2020-06-23 20:33 ` Peter Zijlstra
2020-06-24 9:00 ` Peter Zijlstra
2020-06-24 10:17 ` Marco Elver
2020-06-24 12:31 ` Peter Zijlstra
2020-06-24 11:32 ` Marco Elver
2020-06-24 15:18 ` Peter Zijlstra
2020-07-11 10:09 ` [tip: locking/core] kcsan: Make KCSAN compatible with new IRQ state tracking tip-bot2 for Marco Elver
2020-06-30 5:59 ` [PATCH v4 7/8] lockdep: Change hardirq{s_enabled,_context} to per-cpu variables Ahmed S. Darwish
2020-06-30 9:40 ` Peter Zijlstra
2020-07-11 10:09 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-06-23 8:36 ` [PATCH v4 8/8] lockdep: Remove lockdep_hardirq{s_enabled,_context}() argument Peter Zijlstra
2020-07-11 10:09 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200623181232.GB4800@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=a.darwish@linutronix.de \
--cc=bigeasy@linutronix.de \
--cc=davem@davemloft.net \
--cc=elver@google.com \
--cc=heiko.carstens@de.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=linux@armlinux.org.uk \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mingo@kernel.org \
--cc=mpe@ellerman.id.au \
--cc=rostedt@goodmis.org \
--cc=sparclinux@vger.kernel.org \
--cc=tglx@linutronix.de \
--cc=will@kernel.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).