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Subject[PATCH] printk: fix softlockup/rcu stall warning without setting CONFIG_PREEMPTION
Date
If without setting CONFIG_PREEMPTION, and there are too many messages
only in one cpu which will set console_may_schedule to 0 without cond_resched,
we will find softlockup/rcu stall warning. Although the timer interrupt
can be raised in the routine of console_unlock, the irq interrupt return
to user/kernel will't schedule other tasks(without setting CONFIG_PREEMPTION).
So I add need_resched() for cond_schedule to avoid it.

Call trace:
console_unlock+0x220/0x420
vprintk_emit+0x17c/0x1ac
vprintk_default+0x3c/0x44
vprintk+0x38/0x70
printk+0x64/0x88
dump_task.part.0+0xc4/0xe0
dump_task+0x70/0x74
dump_tasks+0x78/0x90
dump_global_header+0xcc/0xe8
oom_kill_process+0x258/0x274
out_of_memory.part.0+0xb0/0x33c
out_of_memory+0x4c/0xa0
__alloc_pages_may_oom+0x11c/0x1a0
__alloc_pages_slowpath.constprop.0+0x4c0/0x75c
__alloc_pages_nodemask+0x2b4/0x310
alloc_pages_current+0x8c/0x140
get_zeroed_page+0x20/0x50
__pud_alloc+0x40/0x190
copy_pud_range+0x264/0x280
copy_page_range+0xe8/0x204
dup_mmap+0x334/0x434
dup_mm+0x64/0x11c
copy_process+0x5e0/0x11a0
kernel_clone+0x94/0x364
__do_sys_clone+0x54/0x80
__arm64_sys_clone+0x24/0x30
el0_svc_common.constprop.0+0x7c/0x210
do_el0_svc+0x74/0x90
el0_svc+0x24/0x60
el0_sync_handler+0xa8/0xb0
el0_sync+0x140/0x180

Signed-off-by: Guanghui Feng <guanghuifeng@linux.alibaba.com>
---
kernel/printk/printk.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 82abfaf..54b6cf2 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2716,7 +2716,11 @@ void console_unlock(void)
if (handover)
return;

+#ifndef CONFIG_PREEMPTION
+ if (do_cond_resched || need_resched())
+#else
if (do_cond_resched)
+#endif
cond_resched();
}

--
1.8.3.1
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