[PATCH] printk: fix softlockup/rcu stall warning without setting CONFIG_PREEMPTION

[Guanghui Feng]

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@xxxxxxxxxxxxxxxxx>
---
 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