* [PATCH RFC tip/core/rcu 1/2] rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common() [not found] <20200313024007.GA27492@paulmck-ThinkPad-P72> @ 2020-03-13 2:40 ` paulmck 2020-03-13 3:52 ` Joel Fernandes 0 siblings, 1 reply; 3+ messages in thread From: paulmck @ 2020-03-13 2:40 UTC (permalink / raw) To: rcu Cc: linux-kernel, kernel-team, mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh, tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg, joel, Paul E. McKenney, # 5 . 5 . x 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)) { -- 2.9.5 ^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH RFC tip/core/rcu 1/2] rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common() 2020-03-13 2:40 ` [PATCH RFC tip/core/rcu 1/2] rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common() paulmck @ 2020-03-13 3:52 ` Joel Fernandes 2020-03-13 21:47 ` Paul E. McKenney 0 siblings, 1 reply; 3+ messages in thread From: Joel Fernandes @ 2020-03-13 3:52 UTC (permalink / raw) To: paulmck Cc: rcu, linux-kernel, kernel-team, mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh, tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg, # 5 . 5 . x 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 > ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH RFC tip/core/rcu 1/2] rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common() 2020-03-13 3:52 ` Joel Fernandes @ 2020-03-13 21:47 ` Paul E. McKenney 0 siblings, 0 replies; 3+ messages in thread From: Paul E. McKenney @ 2020-03-13 21:47 UTC (permalink / raw) To: Joel Fernandes Cc: rcu, linux-kernel, kernel-team, mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh, tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg, # 5 . 5 . x 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 > > ^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-03-13 2:40 ` [PATCH RFC tip/core/rcu 1/2] rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common() paulmck
2020-03-13 3:52 ` Joel Fernandes
2020-03-13 21:47 ` Paul E. McKenney
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