linux-kernel - Re: [PATCH 0/2] Fix BUG: Invalid wait context in hrtimer

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Message-ID: <YA+em8XkTidYetGE@jagdpanzerIV.localdomain>
Date:   Tue, 26 Jan 2021 13:46:19 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Qais Yousef <qais.yousef@....com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Fix BUG: Invalid wait context in hrtimer_interrupt()

On (21/01/23 23:37), Qais Yousef wrote:
> 
> I hit a pr_warn() inside hrtimer_interrupt() which lead to a BUG: Invalid wait
> context splat.
> 
> The problem wasn't reproducible but I think the cause is obvious, printk can't
> be called from interrupt context.
> 
> AFAICU printk_deferred() is safe from NMI, so I assumed it is safe to be called
> from hrtimer_interrupt() too. Adding a pr_warn_once() inside
> hrtimer_interrupt() in a location where it is always hit produces the BUG
> splat. Replacing it with pr_warn_deferred_once() generates the printk warning
> without any splat.

Could you please post the lockdep splat?
Why is it invalid? Is this... -rt kernel, perhaps?

	-ss