Re: __local_bh_enable_ip() vs lockdep
On Fri, Dec 18, 2020 at 04:37:16PM +0100, Peter Zijlstra wrote:
> On Fri, Dec 18, 2020 at 04:33:56PM +0100, Heiko Carstens wrote:
>
> > Peter, will you make proper patch out of this?
>
> Yes, let me go do that now, and stick it in the quilt series before I go
> off and don't think for 2 weeks.
As below, I'll try and push it out to tip/locking/urgent before I really
dissapear.
---
Subject: softirq: Avoid bad tracing / lockdep interaction
From: Peter Zijlstra
Date: Fri Dec 18 16:39:14 CET 2020
Similar to commit:
1a63dcd8765b ("softirq: Reorder trace_softirqs_on to prevent lockdep splat")
__local_bh_enable_ip() can also call into tracing with inconsistent
state. Unlike that commit we don't need to bother about the tracepoint
because 'cnt-1' never matches preempt_count() (by construction).
Reported-by: Heiko Carstens
Signed-off-by: Peter Zijlstra (Intel)
Tested-by: Heiko Carstens
---
kernel/softirq.c |2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -186,7 +186,7 @@ void __local_bh_enable_ip(unsigned long
* Keep preemption disabled until we are done with
* softirq processing:
*/
- preempt_count_sub(cnt - 1);
+ __preempt_count_sub(cnt - 1);
if (unlikely(!in_interrupt() && local_softirq_pending())) {
/*
Re: __local_bh_enable_ip() vs lockdep
On Fri, Dec 18, 2020 at 04:33:56PM +0100, Heiko Carstens wrote: > Peter, will you make proper patch out of this? Yes, let me go do that now, and stick it in the quilt series before I go off and don't think for 2 weeks.
Re: __local_bh_enable_ip() vs lockdep
On Wed, Dec 16, 2020 at 06:52:59PM +0100, Peter Zijlstra wrote:
> On Tue, Dec 15, 2020 at 02:47:24PM -0500, Steven Rostedt wrote:
> > On Tue, 15 Dec 2020 20:01:52 +0100
> > Heiko Carstens wrote:
> >
> > > Hello,
> > >
> > > the ftrace stack tracer kernel selftest is able to trigger the warning
> > > below from time to time. This looks like there is an ordering problem
> > > in __local_bh_enable_ip():
> > > first there is a call to lockdep_softirqs_on() and afterwards
> > > preempt_count_sub() is ftraced before it was able to modify
> > > preempt_count:
> >
> > Don't run ftrace stack tracer when debugging lockdep. ;-)
> >
> > /me runs!
>
> Ha!, seriously though; that seems like something we've encountered
> before, but my google-fu is failing me.
>
> Do you remember what, if anything, was the problem with this?
>
> ---
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index d5bfd5e661fc..9d71046ea247 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -186,7 +186,7 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int
> cnt)
>* Keep preemption disabled until we are done with
>* softirq processing:
>*/
> - preempt_count_sub(cnt - 1);
> + __preempt_count_sub(cnt - 1);
>
> if (unlikely(!in_interrupt() && local_softirq_pending())) {
> /*
FWIW,
Tested-by: Heiko Carstens
Peter, will you make proper patch out of this?
Re: __local_bh_enable_ip() vs lockdep
On Wed, Dec 16, 2020 at 06:52:59PM +0100, Peter Zijlstra wrote:
> On Tue, Dec 15, 2020 at 02:47:24PM -0500, Steven Rostedt wrote:
> > On Tue, 15 Dec 2020 20:01:52 +0100
> > Heiko Carstens wrote:
> >
> > > Hello,
> > >
> > > the ftrace stack tracer kernel selftest is able to trigger the warning
> > > below from time to time. This looks like there is an ordering problem
> > > in __local_bh_enable_ip():
> > > first there is a call to lockdep_softirqs_on() and afterwards
> > > preempt_count_sub() is ftraced before it was able to modify
> > > preempt_count:
> >
> > Don't run ftrace stack tracer when debugging lockdep. ;-)
> >
> > /me runs!
>
> Ha!, seriously though; that seems like something we've encountered
> before, but my google-fu is failing me.
>
> Do you remember what, if anything, was the problem with this?
Actually this looks like:
1a63dcd8765b ("softirq: Reorder trace_softirqs_on to prevent lockdep splat")
I can give it a test, but it looks quite obvious that your patch will
make the problem go away.
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index d5bfd5e661fc..9d71046ea247 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -186,7 +186,7 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int
> cnt)
>* Keep preemption disabled until we are done with
>* softirq processing:
>*/
> - preempt_count_sub(cnt - 1);
> + __preempt_count_sub(cnt - 1);
>
> if (unlikely(!in_interrupt() && local_softirq_pending())) {
> /*
>
Re: __local_bh_enable_ip() vs lockdep
On Tue, Dec 15, 2020 at 02:47:24PM -0500, Steven Rostedt wrote:
> On Tue, 15 Dec 2020 20:01:52 +0100
> Heiko Carstens wrote:
>
> > Hello,
> >
> > the ftrace stack tracer kernel selftest is able to trigger the warning
> > below from time to time. This looks like there is an ordering problem
> > in __local_bh_enable_ip():
> > first there is a call to lockdep_softirqs_on() and afterwards
> > preempt_count_sub() is ftraced before it was able to modify
> > preempt_count:
>
> Don't run ftrace stack tracer when debugging lockdep. ;-)
>
> /me runs!
Ha!, seriously though; that seems like something we've encountered
before, but my google-fu is failing me.
Do you remember what, if anything, was the problem with this?
---
diff --git a/kernel/softirq.c b/kernel/softirq.c
index d5bfd5e661fc..9d71046ea247 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -186,7 +186,7 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int
cnt)
* Keep preemption disabled until we are done with
* softirq processing:
*/
- preempt_count_sub(cnt - 1);
+ __preempt_count_sub(cnt - 1);
if (unlikely(!in_interrupt() && local_softirq_pending())) {
/*
Re: __local_bh_enable_ip() vs lockdep
On Tue, 15 Dec 2020 20:01:52 +0100 Heiko Carstens wrote: > Hello, > > the ftrace stack tracer kernel selftest is able to trigger the warning > below from time to time. This looks like there is an ordering problem > in __local_bh_enable_ip(): > first there is a call to lockdep_softirqs_on() and afterwards > preempt_count_sub() is ftraced before it was able to modify > preempt_count: Don't run ftrace stack tracer when debugging lockdep. ;-) /me runs! -- Steve > > [ 1016.245418] [ cut here ] > [ 1016.245428] DEBUG_LOCKS_WARN_ON(current->softirqs_enabled) > [ 1016.245441] WARNING: CPU: 8 PID: 8300 at kernel/locking/lockdep.c:5298 > check_flags.part.0+0x196/0x208 > [ 1016.245580] CPU: 8 PID: 8300 Comm: sshd Not tainted > 5.11.0-20201215.rc0.git0.d33ce49dca6c.300.fc33.s390x+debug #1 > ... > [ 1016.245691] Call Trace: > [ 1016.245698] [<4c1537fa>] check_flags.part.0+0x19a/0x208 > [ 1016.245705] ([<4c1537f6>] check_flags.part.0+0x196/0x208) > [ 1016.245711] [<4cced786>] lock_is_held_type+0x8e/0x1b8 > [ 1016.245716] [<4c172924>] rcu_read_lock_sched_held+0x64/0xb8 > [ 1016.245724] [<4c1b151c>] module_assert_mutex_or_preempt+0x34/0x68 > [ 1016.245730] [<4c1b2e04>] __module_address.part.0+0x2c/0x118 > [ 1016.245735] [<4c1b9dca>] __module_text_address+0x3a/0x90 > [ 1016.245741] [<4c1b9ed4>] is_module_text_address+0x34/0x78 > [ 1016.245748] [<4c0f9a1a>] kernel_text_address+0x5a/0x130 > [ 1016.245752] [<4c0f9b16>] __kernel_text_address+0x26/0x70 > [ 1016.245757] [<4c094038>] unwind_get_return_address+0x40/0x68 > [ 1016.245763] [<4c099dac>] arch_stack_walk+0xac/0xd0 > [ 1016.245768] [<4c18be10>] stack_trace_save+0x50/0x68 > [ 1016.245774] [<4c22d80c>] check_stack+0xc4/0x348 > [ 1016.245780] [<4c22db46>] stack_trace_call+0xb6/0xd0 > [ 1016.245785] [<4cd00082>] ftrace_caller+0x7a/0x7e > [ 1016.245791] [<4c1081d6>] preempt_count_sub+0x6/0x138 <--- > [ 1016.245795] [<4c0d3d46>] __local_bh_enable_ip+0x13e/0x190 <--- > [ 1016.245811] [<03ff8023c34c>] nft_update_chain_stats+0xdc/0x168 > [nf_tables] > [ 1016.245820] [<03ff8023c916>] nft_do_chain+0x53e/0x550 [nf_tables] > [ 1016.245827] [<03ff80251974>] nft_do_chain_ipv4+0x6c/0x78 [nf_tables] > [ 1016.245833] [<4cb0ab00>] nf_hook_slow+0x58/0xf8 > [ 1016.245839] [<4cb1dc24>] nf_hook.constprop.0+0xfc/0x1d0 > [ 1016.245844] [<4cb207b2>] __ip_local_out+0x92/0xe8 > [ 1016.245848] [<4cb20d00>] __ip_queue_xmit+0x1d8/0x640 > [ 1016.245854] [<4cb4578c>] __tcp_transmit_skb+0x3dc/0x770 > [ 1016.245858] [<4cb46e86>] tcp_write_xmit+0x38e/0x758 > [ 1016.245863] [<4cb47298>] __tcp_push_pending_frames+0x48/0x118 > [ 1016.245868] [<4cb2f604>] tcp_sendmsg_locked+0x95c/0xb78 > [ 1016.245872] [<4cb2f864>] tcp_sendmsg+0x44/0x68 > [ 1016.245878] [<4ca30c3c>] sock_sendmsg+0x64/0x78 > [ 1016.245882] [<4ca30cc2>] sock_write_iter+0x72/0x98 > [ 1016.245887] [<4c3dcfda>] new_sync_write+0x10a/0x198 > [ 1016.245891] [<4c3dd6a6>] vfs_write.part.0+0x196/0x290 > [ 1016.245896] [<4c3e0220>] ksys_write+0xb8/0xf8 > [ 1016.245900] [<4ccfd326>] system_call+0xe2/0x29c > [ 1016.245904] INFO: lockdep is turned off.
