powerpc/powernv: Fix NVRAM sleep in invalid context when crashing

Similarly to opal_event_shutdown, opal_nvram_write can be called in
the crash path with irqs disabled. Special case the delay to avoid
sleeping in invalid context.

Fixes: 3b807033 ("powerpc/powernv: Fix OPAL NVRAM driver OPAL_BUSY loops")
Cc: stable@vger.kernel.org # v3.2
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/opal-nvram.c

@@ -44,6 +44,10 @@ static ssize_t opal_nvram_read(char *buf, size_t count, loff_t *index)
 	return count;
 }
 
+/*
+ * This can be called in the panic path with interrupts off, so use
+ * mdelay in that case.
+ */
 static ssize_t opal_nvram_write(char *buf, size_t count, loff_t *index)
 {
 	s64 rc = OPAL_BUSY;
@@ -58,9 +62,15 @@ static ssize_t opal_nvram_write(char *buf, size_t count, loff_t *index)
 	while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
 		rc = opal_write_nvram(__pa(buf), count, off);
 		if (rc == OPAL_BUSY_EVENT) {
+			if (in_interrupt() || irqs_disabled())
+				mdelay(OPAL_BUSY_DELAY_MS);
+			else
 				msleep(OPAL_BUSY_DELAY_MS);
 			opal_poll_events(NULL);
 		} else if (rc == OPAL_BUSY) {
+			if (in_interrupt() || irqs_disabled())
+				mdelay(OPAL_BUSY_DELAY_MS);
+			else
 				msleep(OPAL_BUSY_DELAY_MS);
 		}
 	}