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

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Message-ID: <YBBA81osV7cHN2fb@hirez.programming.kicks-ass.net>
Date:   Tue, 26 Jan 2021 17:18:59 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Qais Yousef <qais.yousef@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Fix BUG: Invalid wait context in hrtimer_interrupt()

On Tue, Jan 26, 2021 at 04:28:42PM +0106, John Ogness wrote:
> On 2021-01-26, Qais Yousef <qais.yousef@....com> wrote:
> > 	[67628.393550] =============================
> > 	[67628.393554] [ BUG: Invalid wait context ]
> > 	[67628.393557] 5.11.0-rc3-00019-g86be331946f7 #37 Not tainted
> > 	[67628.393560] -----------------------------
> > 	[67628.393563] sugov:0/192 is trying to lock:
> > 	[67628.393566] ffff000800b1d898 (&port_lock_key){-.-.}-{3:3}, at: pl011_console_write+0x138/0x218
> > 	[67628.393581] other info that might help us debug this:
> > 	[67628.393584] context-{2:2}
> > 	[67628.393586] 4 locks held by sugov:0/192:
> > 	[67628.393589]  #0: ffff0008059cb720 (&sg_policy->work_lock){+.+.}-{4:4}, at: sugov_work+0x58/0x88
> > 	[67628.393603]  #1: ffff800015446f20 (prepare_lock){+.+.}-{4:4}, at: clk_prepare_lock+0x34/0xb0


> pl011_console_write() does:
> 
>     local_irq_save(flags);
>     spin_lock(&uap->port.lock);
> 
> This needs to be:
> 
>     spin_lock_irqsave(&uap->port.lock, flags);
> 
> Of course, it will be a trickier than that because of the
> @oops_in_progress madness. This bug has been around for quite a while.

Well yes, but that's not going to be fixing anything.

The problem is that sugov_work() is holding a raw_spin_lock, and you're
trying to acquire a spin_lock.

That's an invalid lock nesting.