linux-kernel - Re: "BUG: Invalid wait context" in invalidate_batched

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Date:   Fri, 28 Jan 2022 17:04:13 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Jonathan Neuschäfer <j.neuschaefer@....net>,
        Andy Lutomirski <luto@...capital.net>,
        LKML <linux-kernel@...r.kernel.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: "BUG: Invalid wait context" in invalidate_batched_entropy

Hi Sebastian/Jonathan,

On Fri, Jan 28, 2022 at 9:35 AM Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
> This report is due to CONFIG_PROVE_LOCKING=y _and_
> CONFIG_PROVE_RAW_LOCK_NESTING=y. It reports a nesting problem
> (raw_spinlock_t -> spinlock_t lock ordering) which becomes a real
> problem on PREEMPT_RT.

Hmm, I'm still having a tough time reproducing this. I'm trying to
understand your intuition. Is the problem you see that something else
in the IRQ path uses a raw_spinlock_t, and then with that lock still
held, we call invalidate_batched_entropy(), which takes an ordinary
spinlock_t, non-raw? And taking a spinlock-t while holding a
raw_spinlock_t is illegal?

Jason