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SubjectRe: [BUG] local_softirq_pending storm

* Chuck Ebbert <cebbert@redhat.com> wrote:

> > if (need_resched() && system_state == SYSTEM_RUNNING) {
> > - raw_local_irq_disable();
> > - _local_bh_enable();
> > - raw_local_irq_enable();
> > + local_bh_enable();
> > __cond_resched();
> > local_bh_disable();
> > return 1;
>
> We may have a problem with that:
>
> BUG: warning at kernel/softirq.c:138/local_bh_enable() (Not tainted)
> [<c042b2ef>] local_bh_enable+0x45/0x92
> [<c06036b7>] cond_resched_softirq+0x2c/0x42
> [<c059d5d0>] release_sock+0x54/0xa3
> [<c05c9428>] tcp_sendmsg+0x91b/0xa0c
> [<c05e1bb9>] inet_sendmsg+0x3b/0x45
> [<c059af34>] sock_aio_write+0xf9/0x105
> [<c0476035>] do_sync_write+0xc7/0x10a
> [<c0437265>] autoremove_wake_function+0x0/0x35
> [<c047688e>] vfs_write+0xbc/0x154
> [<c0476e8c>] sys_write+0x41/0x67
> [<c0404f70>] syscall_call+0x7/0xb

hm, this place really shouldnt call cond_resched_softirq() with hardirqs
disabled.

perhaps a buggy ->sk_backlog_rcv() handler disabled interrupts without
restoring them?

could you enable CONFIG_PROVE_LOCKING and apply the patch below - which
location is printed as having last disabled hardirqs?

Ingo

--------------------->
Subject: [patch] softirqs: print out irq-trace events
From: Ingo Molnar <mingo@elte.hu>

some code is fiddling with softirqs but hardirqs are disabled, so try to
figure out who disabled hardirqs.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/softirq.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

Index: linux/kernel/softirq.c
===================================================================
--- linux.orig/kernel/softirq.c
+++ linux/kernel/softirq.c
@@ -135,7 +135,15 @@ void local_bh_enable(void)

WARN_ON_ONCE(in_irq());
#endif
- WARN_ON_ONCE(irqs_disabled());
+ if (irqs_disabled()) {
+ static int once = 1;
+
+ if (once) {
+ once = 0;
+ print_irqtrace_events(current);
+ WARN_ON(1);
+ }
+ }

#ifdef CONFIG_TRACE_IRQFLAGS
local_irq_save(flags);
-
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