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rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common()

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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: 5b14557b07 ("rcu: Avoid tick_dep_set_cpu() misordering")
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <stable@vger.kernel.org> # 5.5.x
This commit is contained in:
Paul E. McKenney 2020-03-12 16:55:07 -07:00
parent aa93ec620b
commit bf37da98c5
1 changed files with 1 additions and 1 deletions
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2
kernel/rcu/tree.c
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@ -825,7 +825,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq)
rcu_cleanup_after_idle();
incby = 1;
} else if (tick_nohz_full_cpu(rdp->cpu) &&
} else if (irq && tick_nohz_full_cpu(rdp->cpu) &&
rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE &&
READ_ONCE(rdp->rcu_urgent_qs) &&
!READ_ONCE(rdp->rcu_forced_tick)) {