* rcu: Add might_sleep() check to synchronize_rcu()
@ 2018-03-23 21:12 Thomas Gleixner
2018-03-23 21:28 ` Steven Rostedt
2018-03-25 18:50 ` Paul E. McKenney
0 siblings, 2 replies; 9+ messages in thread
From: Thomas Gleixner @ 2018-03-23 21:12 UTC (permalink / raw)
To: LKML
Cc: Paul E. McKenney, Peter Zijlstra, Josh Triplett, Steven Rostedt,
Mathieu Desnoyers, Lai Jiangshan, Joel Fernandes
Subject: rcu: Add might_sleep() check to synchronize_rcu()
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 23 Mar 2018 22:02:18 +0100
Joel reported a debugobjects warning which is triggered by a RCU callback
invoking synchronize_rcu(). RCU callbacks run in softirq context, so
calling synchronize_rcu() is a bad idea as it might sleep.
debugobjects triggers because __wait_rcu_gp() uses on stack objects and
invokes debug_object_init_on_stack(). That function checks the object
address against current's task stack, which fails because the code runs on
the softirq stack.
synchronize_rcu() lacks a might_sleep() check which would have caught that
issue way earlier because it would trigger with the minimal debug options
enabled.
Add a might_sleep() check to catch such cases.
Reported-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
---
kernel/rcu/tree_plugin.h | 1 +
1 file changed, 1 insertion(+)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -753,6 +753,7 @@ void synchronize_rcu(void)
"Illegal synchronize_rcu() in RCU read-side critical section");
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
return;
+ might_sleep();
if (rcu_gp_is_expedited())
synchronize_rcu_expedited();
else
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: rcu: Add might_sleep() check to synchronize_rcu()
2018-03-23 21:12 rcu: Add might_sleep() check to synchronize_rcu() Thomas Gleixner
@ 2018-03-23 21:28 ` Steven Rostedt
2018-03-23 21:33 ` Thomas Gleixner
2018-03-25 18:50 ` Paul E. McKenney
1 sibling, 1 reply; 9+ messages in thread
From: Steven Rostedt @ 2018-03-23 21:28 UTC (permalink / raw)
To: Thomas Gleixner
Cc: LKML, Paul E. McKenney, Peter Zijlstra, Josh Triplett,
Mathieu Desnoyers, Lai Jiangshan, Joel Fernandes
On Fri, 23 Mar 2018 22:12:24 +0100 (CET)
Thomas Gleixner <tglx@linutronix.de> wrote:
> synchronize_rcu() lacks a might_sleep() check which would have caught that
> issue way earlier because it would trigger with the minimal debug options
> enabled.
>
> Add a might_sleep() check to catch such cases.
I'm not against the patch, but really? I would think that
synchronize_rcu() would pretty much always schedule, and scheduling
from atomic would have triggered with minimal debug options enabled.
-- Steve
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: rcu: Add might_sleep() check to synchronize_rcu()
2018-03-23 21:28 ` Steven Rostedt
@ 2018-03-23 21:33 ` Thomas Gleixner
2018-03-23 21:40 ` Steven Rostedt
0 siblings, 1 reply; 9+ messages in thread
From: Thomas Gleixner @ 2018-03-23 21:33 UTC (permalink / raw)
To: Steven Rostedt
Cc: LKML, Paul E. McKenney, Peter Zijlstra, Josh Triplett,
Mathieu Desnoyers, Lai Jiangshan, Joel Fernandes
On Fri, 23 Mar 2018, Steven Rostedt wrote:
> On Fri, 23 Mar 2018 22:12:24 +0100 (CET)
> Thomas Gleixner <tglx@linutronix.de> wrote:
>
> > synchronize_rcu() lacks a might_sleep() check which would have caught that
> > issue way earlier because it would trigger with the minimal debug options
> > enabled.
> >
> > Add a might_sleep() check to catch such cases.
>
> I'm not against the patch, but really? I would think that
> synchronize_rcu() would pretty much always schedule, and scheduling
> from atomic would have triggered with minimal debug options enabled.
Dunno. The reported splat is here:
https://pastebin.com/raw/puvh0cXE
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: rcu: Add might_sleep() check to synchronize_rcu()
2018-03-23 21:33 ` Thomas Gleixner
@ 2018-03-23 21:40 ` Steven Rostedt
2018-03-23 21:46 ` Thomas Gleixner
2018-03-23 22:57 ` Joel Fernandes
0 siblings, 2 replies; 9+ messages in thread
From: Steven Rostedt @ 2018-03-23 21:40 UTC (permalink / raw)
To: Thomas Gleixner
Cc: LKML, Paul E. McKenney, Peter Zijlstra, Josh Triplett,
Mathieu Desnoyers, Lai Jiangshan, Joel Fernandes
On Fri, 23 Mar 2018 22:33:29 +0100 (CET)
Thomas Gleixner <tglx@linutronix.de> wrote:
> On Fri, 23 Mar 2018, Steven Rostedt wrote:
>
> > On Fri, 23 Mar 2018 22:12:24 +0100 (CET)
> > Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > > synchronize_rcu() lacks a might_sleep() check which would have caught that
> > > issue way earlier because it would trigger with the minimal debug options
> > > enabled.
> > >
> > > Add a might_sleep() check to catch such cases.
> >
> > I'm not against the patch, but really? I would think that
> > synchronize_rcu() would pretty much always schedule, and scheduling
> > from atomic would have triggered with minimal debug options enabled.
>
> Dunno. The reported splat is here:
>
> https://pastebin.com/raw/puvh0cXE
[ 150.560848] ODEBUG: object is not on stack, but annotated
[ 150.566398] ------------[ cut here ]------------
[ 150.571133] WARNING: CPU: 1 PID: 0 at lib/debugobjects.c:300 __debug_object_init+0x526/0xc40
[ 150.579682] Kernel panic - not syncing: panic_on_warn set ...
[ 150.579682]
[ 150.587012] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.89-g960923f #61
[ 150.593906] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
[ 150.603233] ffff8801db307a08 ffffffff81d96069 ffffffff83a482c0 ffff8801db307ae0
[ 150.611190] ffffffff83c19700 ffffffff81dfefb6 0000000000000009 ffff8801db307ad0
[ 150.619157] ffffffff8142fbd1 0000000041b58ab3 ffffffff8418bd08 ffffffff8142fa15
[ 150.627118] Call Trace:
[ 150.629667] <IRQ> [ 150.631700] [<ffffffff81d96069>] dump_stack+0xc1/0x128
[ 150.637051] [<ffffffff81dfefb6>] ? __debug_object_init+0x526/0xc40
[ 150.643431] [<ffffffff8142fbd1>] panic+0x1bc/0x3a8
[ 150.648416] [<ffffffff8142fa15>] ? percpu_up_read_preempt_enable.constprop.53+0xd7/0xd7
[ 150.656611] [<ffffffff81430835>] ? load_image_and_restore+0xf9/0xf9
[ 150.663070] [<ffffffff81269efd>] ? vprintk_default+0x1d/0x30
[ 150.668925] [<ffffffff81131879>] ? __warn+0x1a9/0x1e0
[ 150.674170] [<ffffffff81dfefb6>] ? __debug_object_init+0x526/0xc40
[ 150.680543] [<ffffffff81131894>] __warn+0x1c4/0x1e0
[ 150.685614] [<ffffffff81131afc>] warn_slowpath_null+0x2c/0x40
[ 150.691972] [<ffffffff81dfefb6>] __debug_object_init+0x526/0xc40
[ 150.698174] [<ffffffff81dfea90>] ? debug_object_fixup+0x30/0x30
[ 150.704283] [<ffffffff81dff709>] debug_object_init_on_stack+0x19/0x20
[ 150.710917] [<ffffffff81287a93>] __wait_rcu_gp+0x93/0x1b0
[ 150.716508] [<ffffffff81290251>] synchronize_rcu.part.65+0x101/0x110
[ 150.723054] [<ffffffff81290150>] ? rcu_pm_notify+0xc0/0xc0
[ 150.728735] [<ffffffff81292bc0>] ? __call_rcu.constprop.72+0x910/0x910
[ 150.735459] [<ffffffff81235221>] ? __lock_is_held+0xa1/0xf0
[ 150.741223] [<ffffffff81290287>] synchronize_rcu+0x27/0x90
[ 150.746908] [<ffffffff83588b35>] __l2tp_session_unhash+0x3d5/0x550
Looks like __l2tp_session_unhash() is the real culprit here.
[ 150.753281] [<ffffffff8358891f>] ? __l2tp_session_unhash+0x1bf/0x550
[ 150.759828] [<ffffffff8114596a>] ? __local_bh_enable_ip+0x6a/0xd0
[ 150.766123] [<ffffffff8358ddb0>] ? l2tp_udp_encap_recv+0xd90/0xd90
[ 150.772497] [<ffffffff83588e97>] l2tp_tunnel_closeall+0x1e7/0x3a0
[ 150.778782] [<ffffffff835897be>] l2tp_tunnel_destruct+0x30e/0x5a0
[ 150.785067] [<ffffffff8358965a>] ? l2tp_tunnel_destruct+0x1aa/0x5a0
[ 150.791537] [<ffffffff835894b0>] ? l2tp_tunnel_del_work+0x460/0x460
[ 150.797997] [<ffffffff82ee8053>] __sk_destruct+0x53/0x570
[ 150.803588] [<ffffffff81293918>] rcu_process_callbacks+0x898/0x1300
[ 150.810048] [<ffffffff812939f7>] ? rcu_process_callbacks+0x977/0x1300
[ 150.816684] [<ffffffff82ee8000>] ? __sk_dst_check+0x240/0x240
[ 150.822625] [<ffffffff838be5d6>] __do_softirq+0x206/0x951
[ 150.828223] [<ffffffff81147315>] irq_exit+0x165/0x190
[ 150.833557] [<ffffffff838bd1eb>] smp_apic_timer_interrupt+0x7b/0xa0
[ 150.840018] [<ffffffff838b9470>] apic_timer_interrupt+0xa0/0xb0
[ 150.846132] <EOI> [ 150.848166] [<ffffffff838b6756>] ? native_safe_halt+0x6/0x10
[ 150.854036] [<ffffffff8123bf2d>] ? trace_hardirqs_on+0xd/0x10
[ 150.859973] [<ffffffff838b5d85>] default_idle+0x55/0x360
[ 150.865478] [<ffffffff8106be0a>] arch_cpu_idle+0xa/0x10
I think you want this instead, as __l2tp_session_unhash is what looks
like might be hiding the call to synchronize_rcu(). It's not called in
all instances, and I don't think your patch would have triggered the
issues before hand. You want this:
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 194a7483bb93..857b494bee29 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1677,6 +1677,8 @@ void __l2tp_session_unhash(struct l2tp_session *session)
{
struct l2tp_tunnel *tunnel = session->tunnel;
+ might_sleep();
+
/* Remove the session from core hashes */
if (tunnel) {
/* Remove from the per-tunnel hash */
-- Steve
^ permalink raw reply related [flat|nested] 9+ messages in thread* Re: rcu: Add might_sleep() check to synchronize_rcu()
2018-03-23 21:40 ` Steven Rostedt
@ 2018-03-23 21:46 ` Thomas Gleixner
2018-03-23 22:57 ` Joel Fernandes
1 sibling, 0 replies; 9+ messages in thread
From: Thomas Gleixner @ 2018-03-23 21:46 UTC (permalink / raw)
To: Steven Rostedt
Cc: LKML, Paul E. McKenney, Peter Zijlstra, Josh Triplett,
Mathieu Desnoyers, Lai Jiangshan, Joel Fernandes, netdev,
James Chapman
On Fri, 23 Mar 2018, Steven Rostedt wrote:
> On Fri, 23 Mar 2018 22:33:29 +0100 (CET)
> [ 150.741223] [<ffffffff81290287>] synchronize_rcu+0x27/0x90
> [ 150.746908] [<ffffffff83588b35>] __l2tp_session_unhash+0x3d5/0x550
>
> Looks like __l2tp_session_unhash() is the real culprit here.
Yes. I reported that to netdev already.
> [ 150.753281] [<ffffffff8358891f>] ? __l2tp_session_unhash+0x1bf/0x550
> [ 150.759828] [<ffffffff8114596a>] ? __local_bh_enable_ip+0x6a/0xd0
> [ 150.766123] [<ffffffff8358ddb0>] ? l2tp_udp_encap_recv+0xd90/0xd90
> [ 150.772497] [<ffffffff83588e97>] l2tp_tunnel_closeall+0x1e7/0x3a0
> [ 150.778782] [<ffffffff835897be>] l2tp_tunnel_destruct+0x30e/0x5a0
> [ 150.785067] [<ffffffff8358965a>] ? l2tp_tunnel_destruct+0x1aa/0x5a0
> [ 150.791537] [<ffffffff835894b0>] ? l2tp_tunnel_del_work+0x460/0x460
> [ 150.797997] [<ffffffff82ee8053>] __sk_destruct+0x53/0x570
> [ 150.803588] [<ffffffff81293918>] rcu_process_callbacks+0x898/0x1300
> [ 150.810048] [<ffffffff812939f7>] ? rcu_process_callbacks+0x977/0x1300
> [ 150.816684] [<ffffffff82ee8000>] ? __sk_dst_check+0x240/0x240
> [ 150.822625] [<ffffffff838be5d6>] __do_softirq+0x206/0x951
> [ 150.828223] [<ffffffff81147315>] irq_exit+0x165/0x190
> [ 150.833557] [<ffffffff838bd1eb>] smp_apic_timer_interrupt+0x7b/0xa0
> [ 150.840018] [<ffffffff838b9470>] apic_timer_interrupt+0xa0/0xb0
> [ 150.846132] <EOI> [ 150.848166] [<ffffffff838b6756>] ? native_safe_halt+0x6/0x10
> [ 150.854036] [<ffffffff8123bf2d>] ? trace_hardirqs_on+0xd/0x10
> [ 150.859973] [<ffffffff838b5d85>] default_idle+0x55/0x360
> [ 150.865478] [<ffffffff8106be0a>] arch_cpu_idle+0xa/0x10
>
> I think you want this instead, as __l2tp_session_unhash is what looks
> like might be hiding the call to synchronize_rcu(). It's not called in
> all instances, and I don't think your patch would have triggered the
> issues before hand. You want this:
>
> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> index 194a7483bb93..857b494bee29 100644
> --- a/net/l2tp/l2tp_core.c
> +++ b/net/l2tp/l2tp_core.c
> @@ -1677,6 +1677,8 @@ void __l2tp_session_unhash(struct l2tp_session *session)
> {
> struct l2tp_tunnel *tunnel = session->tunnel;
>
> + might_sleep();
> +
> /* Remove the session from core hashes */
> if (tunnel) {
> /* Remove from the per-tunnel hash */
That too :)
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: rcu: Add might_sleep() check to synchronize_rcu()
2018-03-23 21:40 ` Steven Rostedt
2018-03-23 21:46 ` Thomas Gleixner
@ 2018-03-23 22:57 ` Joel Fernandes
2018-03-24 1:21 ` Steven Rostedt
1 sibling, 1 reply; 9+ messages in thread
From: Joel Fernandes @ 2018-03-23 22:57 UTC (permalink / raw)
To: Steven Rostedt
Cc: Thomas Gleixner, LKML, Paul E. McKenney, Peter Zijlstra,
Josh Triplett, Mathieu Desnoyers, Lai Jiangshan
On Fri, Mar 23, 2018 at 2:40 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 23 Mar 2018 22:33:29 +0100 (CET)
> Thomas Gleixner <tglx@linutronix.de> wrote:
>
>> On Fri, 23 Mar 2018, Steven Rostedt wrote:
>>
>> > On Fri, 23 Mar 2018 22:12:24 +0100 (CET)
>> > Thomas Gleixner <tglx@linutronix.de> wrote:
>> >
>> > > synchronize_rcu() lacks a might_sleep() check which would have caught that
>> > > issue way earlier because it would trigger with the minimal debug options
>> > > enabled.
>> > >
>> > > Add a might_sleep() check to catch such cases.
>> >
>> > I'm not against the patch, but really? I would think that
>> > synchronize_rcu() would pretty much always schedule, and scheduling
>> > from atomic would have triggered with minimal debug options enabled.
>>
>> Dunno. The reported splat is here:
>>
>> https://pastebin.com/raw/puvh0cXE
>
> [ 150.560848] ODEBUG: object is not on stack, but annotated
> [ 150.566398] ------------[ cut here ]------------
> [ 150.571133] WARNING: CPU: 1 PID: 0 at lib/debugobjects.c:300 __debug_object_init+0x526/0xc40
> [ 150.579682] Kernel panic - not syncing: panic_on_warn set ...
> [ 150.579682]
> [ 150.587012] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.89-g960923f #61
> [ 150.593906] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> [ 150.603233] ffff8801db307a08 ffffffff81d96069 ffffffff83a482c0 ffff8801db307ae0
> [ 150.611190] ffffffff83c19700 ffffffff81dfefb6 0000000000000009 ffff8801db307ad0
> [ 150.619157] ffffffff8142fbd1 0000000041b58ab3 ffffffff8418bd08 ffffffff8142fa15
> [ 150.627118] Call Trace:
> [ 150.629667] <IRQ> [ 150.631700] [<ffffffff81d96069>] dump_stack+0xc1/0x128
> [ 150.637051] [<ffffffff81dfefb6>] ? __debug_object_init+0x526/0xc40
> [ 150.643431] [<ffffffff8142fbd1>] panic+0x1bc/0x3a8
> [ 150.648416] [<ffffffff8142fa15>] ? percpu_up_read_preempt_enable.constprop.53+0xd7/0xd7
> [ 150.656611] [<ffffffff81430835>] ? load_image_and_restore+0xf9/0xf9
> [ 150.663070] [<ffffffff81269efd>] ? vprintk_default+0x1d/0x30
> [ 150.668925] [<ffffffff81131879>] ? __warn+0x1a9/0x1e0
> [ 150.674170] [<ffffffff81dfefb6>] ? __debug_object_init+0x526/0xc40
> [ 150.680543] [<ffffffff81131894>] __warn+0x1c4/0x1e0
> [ 150.685614] [<ffffffff81131afc>] warn_slowpath_null+0x2c/0x40
> [ 150.691972] [<ffffffff81dfefb6>] __debug_object_init+0x526/0xc40
> [ 150.698174] [<ffffffff81dfea90>] ? debug_object_fixup+0x30/0x30
> [ 150.704283] [<ffffffff81dff709>] debug_object_init_on_stack+0x19/0x20
> [ 150.710917] [<ffffffff81287a93>] __wait_rcu_gp+0x93/0x1b0
> [ 150.716508] [<ffffffff81290251>] synchronize_rcu.part.65+0x101/0x110
> [ 150.723054] [<ffffffff81290150>] ? rcu_pm_notify+0xc0/0xc0
> [ 150.728735] [<ffffffff81292bc0>] ? __call_rcu.constprop.72+0x910/0x910
> [ 150.735459] [<ffffffff81235221>] ? __lock_is_held+0xa1/0xf0
> [ 150.741223] [<ffffffff81290287>] synchronize_rcu+0x27/0x90
> [ 150.746908] [<ffffffff83588b35>] __l2tp_session_unhash+0x3d5/0x550
>
> Looks like __l2tp_session_unhash() is the real culprit here.
>
> [ 150.753281] [<ffffffff8358891f>] ? __l2tp_session_unhash+0x1bf/0x550
> [ 150.759828] [<ffffffff8114596a>] ? __local_bh_enable_ip+0x6a/0xd0
> [ 150.766123] [<ffffffff8358ddb0>] ? l2tp_udp_encap_recv+0xd90/0xd90
> [ 150.772497] [<ffffffff83588e97>] l2tp_tunnel_closeall+0x1e7/0x3a0
> [ 150.778782] [<ffffffff835897be>] l2tp_tunnel_destruct+0x30e/0x5a0
> [ 150.785067] [<ffffffff8358965a>] ? l2tp_tunnel_destruct+0x1aa/0x5a0
> [ 150.791537] [<ffffffff835894b0>] ? l2tp_tunnel_del_work+0x460/0x460
> [ 150.797997] [<ffffffff82ee8053>] __sk_destruct+0x53/0x570
> [ 150.803588] [<ffffffff81293918>] rcu_process_callbacks+0x898/0x1300
> [ 150.810048] [<ffffffff812939f7>] ? rcu_process_callbacks+0x977/0x1300
> [ 150.816684] [<ffffffff82ee8000>] ? __sk_dst_check+0x240/0x240
> [ 150.822625] [<ffffffff838be5d6>] __do_softirq+0x206/0x951
> [ 150.828223] [<ffffffff81147315>] irq_exit+0x165/0x190
> [ 150.833557] [<ffffffff838bd1eb>] smp_apic_timer_interrupt+0x7b/0xa0
> [ 150.840018] [<ffffffff838b9470>] apic_timer_interrupt+0xa0/0xb0
> [ 150.846132] <EOI> [ 150.848166] [<ffffffff838b6756>] ? native_safe_halt+0x6/0x10
> [ 150.854036] [<ffffffff8123bf2d>] ? trace_hardirqs_on+0xd/0x10
> [ 150.859973] [<ffffffff838b5d85>] default_idle+0x55/0x360
> [ 150.865478] [<ffffffff8106be0a>] arch_cpu_idle+0xa/0x10
>
> I think you want this instead, as __l2tp_session_unhash is what looks
> like might be hiding the call to synchronize_rcu(). It's not called in
> all instances, and I don't think your patch would have triggered the
> issues before hand. You want this:
>
> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> index 194a7483bb93..857b494bee29 100644
> --- a/net/l2tp/l2tp_core.c
> +++ b/net/l2tp/l2tp_core.c
> @@ -1677,6 +1677,8 @@ void __l2tp_session_unhash(struct l2tp_session *session)
> {
> struct l2tp_tunnel *tunnel = session->tunnel;
>
> + might_sleep();
> +
> /* Remove the session from core hashes */
> if (tunnel) {
> /* Remove from the per-tunnel hash */
Thanks Thomas and Steven, also shouldn't this code be calling
synchronize_rcu_bh instead of synchronize_rcu, to complement the
rcu_read_lock_bh? In which situations would you call one versus the
other?
Also it seems rcu_read_lock_bh does a might_sleep already in rcu_blocking_is_gp.
thanks,
- Joel
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: rcu: Add might_sleep() check to synchronize_rcu()
2018-03-23 22:57 ` Joel Fernandes
@ 2018-03-24 1:21 ` Steven Rostedt
2018-03-25 18:43 ` Paul E. McKenney
0 siblings, 1 reply; 9+ messages in thread
From: Steven Rostedt @ 2018-03-24 1:21 UTC (permalink / raw)
To: Joel Fernandes
Cc: Thomas Gleixner, LKML, Paul E. McKenney, Peter Zijlstra,
Josh Triplett, Mathieu Desnoyers, Lai Jiangshan
On Fri, 23 Mar 2018 15:57:04 -0700
Joel Fernandes <joelaf@google.com> wrote:
> > diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> > index 194a7483bb93..857b494bee29 100644
> > --- a/net/l2tp/l2tp_core.c
> > +++ b/net/l2tp/l2tp_core.c
> > @@ -1677,6 +1677,8 @@ void __l2tp_session_unhash(struct l2tp_session *session)
> > {
> > struct l2tp_tunnel *tunnel = session->tunnel;
> >
> > + might_sleep();
> > +
> > /* Remove the session from core hashes */
> > if (tunnel) {
> > /* Remove from the per-tunnel hash */
>
> Thanks Thomas and Steven, also shouldn't this code be calling
> synchronize_rcu_bh instead of synchronize_rcu, to complement the
> rcu_read_lock_bh? In which situations would you call one versus the
> other?
Probably, as the comment above rcu_read_lock_bh is:
* rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
*
* This is equivalent of rcu_read_lock(), but to be used when updates
* are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
* both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
* softirq handler to be a quiescent state, a process in RCU read-side
* critical section must be protected by disabling softirqs.
It appears that the reason to use rcu_read_lock_bh() is if you are
calling synchronize_rcu_bh(). Otherwise, one could just be using
straight rcu_read_lock().
-- Steve
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: rcu: Add might_sleep() check to synchronize_rcu()
2018-03-24 1:21 ` Steven Rostedt
@ 2018-03-25 18:43 ` Paul E. McKenney
0 siblings, 0 replies; 9+ messages in thread
From: Paul E. McKenney @ 2018-03-25 18:43 UTC (permalink / raw)
To: Steven Rostedt
Cc: Joel Fernandes, Thomas Gleixner, LKML, Peter Zijlstra,
Josh Triplett, Mathieu Desnoyers, Lai Jiangshan
On Fri, Mar 23, 2018 at 09:21:05PM -0400, Steven Rostedt wrote:
> On Fri, 23 Mar 2018 15:57:04 -0700
> Joel Fernandes <joelaf@google.com> wrote:
>
> > > diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> > > index 194a7483bb93..857b494bee29 100644
> > > --- a/net/l2tp/l2tp_core.c
> > > +++ b/net/l2tp/l2tp_core.c
> > > @@ -1677,6 +1677,8 @@ void __l2tp_session_unhash(struct l2tp_session *session)
> > > {
> > > struct l2tp_tunnel *tunnel = session->tunnel;
> > >
> > > + might_sleep();
> > > +
> > > /* Remove the session from core hashes */
> > > if (tunnel) {
> > > /* Remove from the per-tunnel hash */
> >
> > Thanks Thomas and Steven, also shouldn't this code be calling
> > synchronize_rcu_bh instead of synchronize_rcu, to complement the
> > rcu_read_lock_bh? In which situations would you call one versus the
> > other?
>
> Probably, as the comment above rcu_read_lock_bh is:
>
> * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
> *
> * This is equivalent of rcu_read_lock(), but to be used when updates
> * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
> * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
> * softirq handler to be a quiescent state, a process in RCU read-side
> * critical section must be protected by disabling softirqs.
>
> It appears that the reason to use rcu_read_lock_bh() is if you are
> calling synchronize_rcu_bh(). Otherwise, one could just be using
> straight rcu_read_lock().
Agreed, these do have to match. (I am still working on collapsing
RCU-preempt, RCU-bh, and RCU-sched into one thing per Linus's request,
but still at the pen-and-paper stage. Not all that difficult, just a
lot of cases to cover.)
Thanx, Paul
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: rcu: Add might_sleep() check to synchronize_rcu()
2018-03-23 21:12 rcu: Add might_sleep() check to synchronize_rcu() Thomas Gleixner
2018-03-23 21:28 ` Steven Rostedt
@ 2018-03-25 18:50 ` Paul E. McKenney
1 sibling, 0 replies; 9+ messages in thread
From: Paul E. McKenney @ 2018-03-25 18:50 UTC (permalink / raw)
To: Thomas Gleixner
Cc: LKML, Peter Zijlstra, Josh Triplett, Steven Rostedt,
Mathieu Desnoyers, Lai Jiangshan, Joel Fernandes
On Fri, Mar 23, 2018 at 10:12:24PM +0100, Thomas Gleixner wrote:
> Subject: rcu: Add might_sleep() check to synchronize_rcu()
> From: Thomas Gleixner <tglx@linutronix.de>
> Date: Fri, 23 Mar 2018 22:02:18 +0100
>
> Joel reported a debugobjects warning which is triggered by a RCU callback
> invoking synchronize_rcu(). RCU callbacks run in softirq context, so
> calling synchronize_rcu() is a bad idea as it might sleep.
>
> debugobjects triggers because __wait_rcu_gp() uses on stack objects and
> invokes debug_object_init_on_stack(). That function checks the object
> address against current's task stack, which fails because the code runs on
> the softirq stack.
>
> synchronize_rcu() lacks a might_sleep() check which would have caught that
> issue way earlier because it would trigger with the minimal debug options
> enabled.
>
> Add a might_sleep() check to catch such cases.
>
> Reported-by: Joel Fernandes <joelaf@google.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Lai Jiangshan <jiangshanlai@gmail.com>
> ---
> kernel/rcu/tree_plugin.h | 1 +
> 1 file changed, 1 insertion(+)
>
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -753,6 +753,7 @@ void synchronize_rcu(void)
> "Illegal synchronize_rcu() in RCU read-side critical section");
> if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
> return;
> + might_sleep();
> if (rcu_gp_is_expedited())
> synchronize_rcu_expedited();
> else
I could add this, but synchronize_rcu_expedited() will do
either a mutex_lock() or a wait_event(), both of which already
have a might_sleep(), and wait_rcu_gp() unconditionally calls
wait_for_completion(), which already has a might_sleep().
Unless there is only one CPU in the system either at early boot. Is
this possibility common enough to warrant a might_sleep() further up?
Thanx, Paul
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2018-03-25 18:49 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-03-23 21:12 rcu: Add might_sleep() check to synchronize_rcu() Thomas Gleixner
2018-03-23 21:28 ` Steven Rostedt
2018-03-23 21:33 ` Thomas Gleixner
2018-03-23 21:40 ` Steven Rostedt
2018-03-23 21:46 ` Thomas Gleixner
2018-03-23 22:57 ` Joel Fernandes
2018-03-24 1:21 ` Steven Rostedt
2018-03-25 18:43 ` Paul E. McKenney
2018-03-25 18:50 ` Paul E. McKenney
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