powerpc/pseries: Cancel RTAS event scan before firmware flash

The RTAS firmware flash update is conducted using an RTAS call that is
serialized by lock_rtas() which uses spin_lock. While the flash is in
progress, rtasd performs scan for any RTAS events that are generated by
the system. rtasd keeps scanning for the RTAS events generated on the
machine. This is performed via workqueue mechanism. The rtas_event_scan()
also uses an RTAS call to scan the events, eventually trying to acquire
the spin_lock before issuing the request.

The flash update takes a while to complete and during this time, any other
RTAS call has to wait. In this case, rtas_event_scan() waits for a long time
on the spin_lock resulting in a soft lockup.

Fix: Just before the flash update is performed, the queued rtas_event_scan()
work item is cancelled from the work queue so that there is no other RTAS
call issued while the flash is in progress. After the flash completes, the
system reboots and the rtas_event_scan() is rescheduled.

Signed-off-by: Suzuki Poulose <suzuki@in.ibm.com>
Signed-off-by: Ravi Nittala <ravi.nittala@in.ibm.com>
Reported-by: Divya Vikas <divya.vikas@in.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/rtas.h

@@ -245,6 +245,12 @@ extern int early_init_dt_scan_rtas(unsigned long node,
 
 extern void pSeries_log_error(char *buf, unsigned int err_type, int fatal);
 
+#ifdef CONFIG_PPC_RTAS_DAEMON
+extern void rtas_cancel_event_scan(void);
+#else
+static inline void rtas_cancel_event_scan(void) { }
+#endif
+
 /* Error types logged.  */
 #define ERR_FLAG_ALREADY_LOGGED	0x0
 #define ERR_FLAG_BOOT		0x1 	/* log was pulled from NVRAM on boot */

arch/powerpc/kernel/rtas_flash.c

@@ -567,6 +567,12 @@ static void rtas_flash_firmware(int reboot_type)
 		return;
 	}
 
+	/*
+	 * Just before starting the firmware flash, cancel the event scan work
+	 * to avoid any soft lockup issues.
+	 */
+	rtas_cancel_event_scan();
+
 	/*
 	 * NOTE: the "first" block must be under 4GB, so we create
 	 * an entry with no data blocks in the reserved buffer in

arch/powerpc/kernel/rtasd.c

@@ -472,6 +472,13 @@ static void start_event_scan(void)
 				 &event_scan_work, event_scan_delay);
 }
 
+/* Cancel the rtas event scan work */
+void rtas_cancel_event_scan(void)
+{
+	cancel_delayed_work_sync(&event_scan_work);
+}
+EXPORT_SYMBOL_GPL(rtas_cancel_event_scan);
+
 static int __init rtas_init(void)
 {
 	struct proc_dir_entry *entry;