Re: [patch V3 01/23] rcu: Dont acquire lock in NMI handler in rcu_nmi_enter_common()

[Frederic Weisbecker]

On Fri, Mar 20, 2020 at 06:59:57PM +0100, Thomas Gleixner wrote:
> From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> 
> The rcu_nmi_enter_common() function can be invoked both in interrupt
> and NMI handlers.  If it is invoked from process context (as opposed
> to userspace or idle context) on a nohz_full CPU, it might acquire the
> CPU's leaf rcu_node structure's ->lock.  Because this lock is held only
> with interrupts disabled, this is safe from an interrupt handler, but
> doing so from an NMI handler can result in self-deadlock.
> 
> This commit therefore adds "irq" to the "if" condition so as to only
> acquire the ->lock from irq handlers or process context, never from
> an NMI handler.
> 
> Fixes: 5b14557b073c ("rcu: Avoid tick_dep_set_cpu() misordering")
> Reported-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> Link: https://lkml.kernel.org/r/20200313024046.27622-1-paulmck@xxxxxxxxxx

Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>