[PATCH] linux-4.19.y/printk: Avoid logbuf_lock deadlock in oops_end()

[Tony W Wang-oc]

A CPU executing vprintk_emit might be interrupted by #PF exception,
this may leads to logbuf_lock deadlock:

CPU x:                            CPU x:
----                              ----
vprintk_emit()
  logbuf_lock_irqsave()
    printk_safe_enter_irqsave()
A:  raw_spin_lock(&logbuf_lock)
  vprintk_store()                 #PF
                                  do_page_fault
                                    ...
                                    oops_end
                                      bust_spinlocks(0)
                                        console_unlock()
                                          ...
                                          printk_safe_enter_irqsave()
B:                                        raw_spin_lock(&logbuf_lock)

logbuf_lock is taken at A and the deadlock happends at B.

Pass 1 to bust_spinlocks() in the oops_end() to avoid this deadlock.

Signed-off-by: Tony W Wang-oc <TonyWWang-oc@xxxxxxxxxxx>
---
 arch/x86/kernel/dumpstack.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 7e698c45760c..b4c145ee9536 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -336,7 +336,7 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
 	if (regs && kexec_should_crash(current))
 		crash_kexec(regs);
 
-	bust_spinlocks(0);
+	bust_spinlocks(1);
 	die_owner = -1;
 	add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
 	die_nest_count--;
-- 
2.25.1