[PATCH] printk: Enhance the condition check of msleep in pr_flush()

[Chao Qin]

There is msleep in pr_flush(). If call WARN() in the early boot
stage such as in early_initcall, pr_flush() will run into msleep
when process scheduler is not ready yet. And then the system will
sleep forever.

Before the system_state is SYSTEM_RUNNING, make sure DO NOT sleep
in pr_flush().

Fixes: c0b395bd0fe3("printk: add pr_flush()")
Signed-off-by: Chao Qin <chao.qin@xxxxxxxxx>
Signed-off-by: Lili Li <lili.li@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/20210719022649.3444072-1-chao.qin@xxxxxxxxx
---
 kernel/printk/printk.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e4085e2cafb5..500ae4b18864 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3661,7 +3661,9 @@ bool pr_flush(int timeout_ms, bool reset_on_progress)
 	u64 diff;
 	u64 seq;
 
-	may_sleep = (preemptible() && !in_softirq());
+	may_sleep = (preemptible() &&
+		     !in_softirq() &&
+		     system_state >= SYSTEM_RUNNING);
 
 	seq = prb_next_seq(prb);
 
-- 
2.20.1