From: Hoeun Ryu <hoeun....@lge.com>
Use printk_safe_flush_on_panic() in nmi_trigger_cpumask_backtrace().
nmi_trigger_cpumask_backtrace() can be called in NMI context. For example the
function is called in watchdog_overflow_callback() if the flag of hardlockup
backtrace (sysctl_hardlockup_all_cpu_backtrace) is true and
watchdog_overflow_callback() function is called in NMI context on some
architectures.
printk_safe_flush() eventually tries to lock logbuf_lock in vprintk_emit() but
the
logbuf_lock can be already locked in preempted contexts (task or irq in this
case)
or by other CPUs and it may cause deadlocks.
By using printk_safe_flush_on_panic() instead of printk_safe_flush() in
in nmi_trigger_cpumask_backtrace(), the backtrace triggering CPU can access the
lock
safely as the lock is reinitialized before calling printk_safe_flush().
The messages in logbuf can be corrupted if the NMI context preempts other
contexts
or ignores the lock held by other CPUs writing the buffer.
Signed-off-by: Hoeun Ryu <hoeun....@lge.com>
---
lib/nmi_backtrace.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
index 61a6b5a..0ace3c9 100644
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -78,8 +78,11 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
/*
* Force flush any remote buffers that might be stuck in IRQ context
* and therefore could not run their irq_work.
+ * Call nmi-safe version of printk_safe_flush() because this function
can be
+ * called in NMI context like watchdog_overflow_callback() if
+ * sysctl_hardlockup_all_cpu_backtrace is true.
*/
- printk_safe_flush();
+ printk_safe_flush_on_panic();
clear_bit_unlock(0, &backtrace_flag);
put_cpu();
--
2.1.4
