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

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Date:   Fri, 28 Jan 2022 17:28:47 +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,

On Fri, Jan 28, 2022 at 5:19 PM Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
> Correct. You must not acquire a spinlock_t while holding a
> raw_spinlock_t. This is because on PREEMPT_RT the spinlock_t is a
> sleeping lock while raw_spinlock_t disables preemption/ interrupts and
> sleeping is not possible.
>         Documentation/locking/locktypes.rst
>
> On non-PREEMPT both lock types (spinlock_t & raw_spinlock_t) behave in
> the same way but lockdep can tell them apart with
> CONFIG_PROVE_RAW_LOCK_NESTING=y and show code that is problematic on RT.

Gotcha. Surely, then, Andy's patch at least goes some of the way
toward fixing this, since it outright _removes_ a spinlock_t. There is
still the other spinlock_t that you want removed, I realize, though
this doesn't appear to be the one from Jonathan's bug report. It
sounds like Andy's patch might be one side of the fix, and your patch
the other?

Jason