linux-kernel - Re: [PATCH v4] lockdep: Fix wait context check on softirq for PREEMPT

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Message-ID: <Z-MoNvnFOQmST8f3@gmail.com>
Date: Tue, 25 Mar 2025 23:03:34 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Jens Axboe <axboe@...nel.dk>, Ryo Takakura <ryotkkr98@...il.com>,
	NeilBrown <neilb@...e.de>,
	Caleb Sander Mateos <csander@...estorage.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Borislav Petkov <bp@...en8.de>, Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>, linux-kernel@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev
Subject: Re: [PATCH v4] lockdep: Fix wait context check on softirq for
 PREEMPT_RT


* Boqun Feng <boqun.feng@...il.com> wrote:

> On Tue, Mar 25, 2025 at 10:42:36AM +0100, Ingo Molnar wrote:
> > 
> > * Boqun Feng <boqun.feng@...il.com> wrote:
> > 
> > > Since commit 0c1d7a2c2d32 ("lockdep: Remove softirq accounting on
> > > PREEMPT_RT."), the wait context test for mutex usage within
> > > "in softirq context" fails as it references @softirq_context.
> > > 
> > > [    0.184549]   | wait context tests |
> > > [    0.184549]   --------------------------------------------------------------------------
> > > [    0.184549]                                  | rcu  | raw  | spin |mutex |
> > > [    0.184549]   --------------------------------------------------------------------------
> > > [    0.184550]                in hardirq context:  ok  |  ok  |  ok  |  ok  |
> > > [    0.185083] in hardirq context (not threaded):  ok  |  ok  |  ok  |  ok  |
> > > [    0.185606]                in softirq context:  ok  |  ok  |  ok  |FAILED|
> > > 
> > > As a fix, add lockdep map for BH disabled section. This fixes the
> > > issue by letting us catch cases when local_bh_disable() gets called
> > > with preemption disabled where local_lock doesn't get acquired.
> > > In the case of "in softirq context" selftest, local_bh_disable() was
> > > being called with preemption disable as it's early in the boot.
> > > 
> > > [boqun: Move the lockdep annotations into __local_bh_*() to avoid false
> > > positives because of unpaired local_bh_disable() reported by Borislav
> > > Petkov [1] and Peter Zijlstra [2], and make bh_lock_map only exist for
> > > PREEMPT_RT]
> > > 
> > > Signed-off-by: Ryo Takakura <ryotkkr98@...il.com>
> > > Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> > > Link: https://lore.kernel.org/all/20250306122413.GBZ8mT7Z61Tmgnh5Y9@fat_crate.local/ [1]
> > > Link: https://lore.kernel.org/lkml/20250307113955.GK16878@noisy.programming.kicks-ass.net/ [2]
> > > Link: https://lore.kernel.org/r/20250118054900.18639-1-ryotkkr98@gmail.com
> > 
> > That's a weird SOB chain. Following back the history of the submission 
> > I believe this line went missing:
> > 
> >   From: Ryo Takakura <ryotkkr98@...il.com>
> > 
> > I added it back in to the commit.
> > 
> 
> Thanks! Looks like I lost the "From:" field when I post the draft of v4
> at:
> 
> 	https://lore.kernel.org/lkml/Z8t8imzJVhWyDvhC@boqun-archlinux/
> 
> I must re-apply that email as a patch to my branch, hence the "From:"
> field got changed. Sorry for the mistakes.

No worries - sometimes when rebasing with a conflict or applying with a 
conflict, Git can drop authorship without much of a warning - I've ran 
into that myself - so it happens.

Thanks,

	Ingo