[PATCH RFC tip/core/rcu 1/2] rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common()
From: "Paul E. McKenney" paulmck@kernel.org
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@linutronix.de Signed-off-by: Paul E. McKenney paulmck@kernel.org Cc: stable@vger.kernel.org # 5.5.x --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d3f52c3..f7d3e48 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -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)) {
On Thu, Mar 12, 2020 at 07:40:45PM -0700, paulmck@kernel.org wrote:
From: "Paul E. McKenney" paulmck@kernel.org
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.
I think Peter's new lockdep changes for NMI would also catch this issue.
Fixes: 5b14557b073c ("rcu: Avoid tick_dep_set_cpu() misordering")
Reviewed-by: Joel Fernandes (Google) joel@joelfernandes.org
thanks,
- Joel
Reported-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Paul E. McKenney paulmck@kernel.org Cc: stable@vger.kernel.org # 5.5.x
kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d3f52c3..f7d3e48 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -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)) {
-- 2.9.5
On Thu, Mar 12, 2020 at 11:52:01PM -0400, Joel Fernandes wrote:
On Thu, Mar 12, 2020 at 07:40:45PM -0700, paulmck@kernel.org wrote:
From: "Paul E. McKenney" paulmck@kernel.org
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.
I think Peter's new lockdep changes for NMI would also catch this issue.
Fixes: 5b14557b073c ("rcu: Avoid tick_dep_set_cpu() misordering")
Reviewed-by: Joel Fernandes (Google) joel@joelfernandes.org
Applied, thank you!!!
Thanx, Paul
thanks,
- Joel
Reported-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Paul E. McKenney paulmck@kernel.org Cc: stable@vger.kernel.org # 5.5.x
kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d3f52c3..f7d3e48 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -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)) {
-- 2.9.5
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