serial: core: Document lock requirement for UPF_* flags updates
The flags field of struct uart_port can only be safely modified
if the port mutex is held; no other lock prevents concurrent
changes from corrupting the field.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index cf3a1e7..8cb267b 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -152,6 +152,7 @@
unsigned long sysrq; /* sysrq timeout */
#endif
+ /* flags must be updated while holding port mutex */
upf_t flags;
#define UPF_FOURPORT ((__force upf_t) (1 << 1))