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

Commit Message

Thomas Gleixner March 20, 2020, 5:59 p.m. UTC

From: "Paul E. McKenney" <[e-mail]>

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 <[e-mail]>
Signed-off-by: Paul E. McKenney <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Reviewed-by: Joel Fernandes (Google) <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

---
 kernel/rcu/tree.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Frederic Weisbecker March 24, 2020, 3:37 p.m. UTC | #1

On Fri, Mar 20, 2020 at 06:59:57PM +0100, Thomas Gleixner wrote:
> From: "Paul E. McKenney" <[e-mail]>
> 
> 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 <[e-mail]>
> Signed-off-by: Paul E. McKenney <[e-mail]>
> Signed-off-by: Thomas Gleixner <[e-mail]>
> Reviewed-by: Joel Fernandes (Google) <[e-mail]>
> Link: https://lkml.kernel.org/r/[e-mail]

Reviewed-by: Frederic Weisbecker <[e-mail]>

Patch

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -816,7 +816,7 @@  static __always_inline void rcu_nmi_ente
 			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) && !rdp->rcu_forced_tick) {
 		raw_spin_lock_rcu_node(rdp->mynode);