linux-kernel - Re: [PATCH] sched: Do not bug in __sched

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Message-ID: <20181119151311.GA5340@kroah.com>
Date:   Mon, 19 Nov 2018 16:13:11 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Laurent Dufour <ldufour@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...l.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] sched: Do not bug in __sched_setscheduler() when pi is
 not used

On Wed, Nov 14, 2018 at 12:55:20PM -0800, Florian Fainelli wrote:
> On 3/9/17 7:18 AM, Steven Rostedt wrote:
> > From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> > 
> > 
> > When priority inheritance was added back in 2.6.18 to sched_setscheduler, it
> > added a path to taking an rt-mutex wait_lock, which is not IRQ safe. As PI
> > is not a common occurrence, lockdep will likely never trigger if
> > sched_setscheduler was called from interrupt context. A BUG_ON() was added
> > to trigger if __sched_setscheduler() was ever called from interrupt context
> > because there was a possibility to take the wait_lock.
> > 
> > Today the wait_lock is irq safe, but the path to taking it in
> > sched_setscheduler() is the same as the path to taking it from normal
> > context. The wait_lock is taken with raw_spin_lock_irq() and released with
> > raw_spin_unlock_irq() which will indiscriminately enable interrupts,
> > which would be bad in interrupt context.
> > 
> > The problem is that normalize_rt_tasks, which is called by triggering the
> > sysrq nice-all-RT-tasks was changed to call __sched_setscheduler(), and this
> > is done from interrupt context!
> > 
> > Now __sched_setscheduler() takes a "pi" parameter that is used to know if
> > the priority inheritance should be called or not. As the BUG_ON() only cares
> > about calling the PI code, it should only bug if called from interrupt
> > context with the "pi" parameter set to true.
> > 
> > Link: http://lkml.kernel.org/r/20170308124654.10e598f2@gandalf.local.home
> > 
> > Reported-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
> > Tested-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
> > Fixes: dbc7f069b93a ("sched: Use replace normalize_task() with __sched_setscheduler()")
> > Cc: Andrew Morton <akpm@...l.org>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Ingo Molnar <mingo@...e.hu>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> 
> Can this patch also be applied to the stable trees? The offending commit
> was first introduced in 4.2.

What is the git commit id of this patch in Linus's tree?

thanks,

greg k-h