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authorSergey Senozhatsky <sergey.senozhatsky.work@gmail.com>2018-12-13 13:58:39 +0900
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-01-26 09:37:04 +0100
commit035438452f85412438be0f6b4dae88b32353cfac (patch)
treebf0a5a5c3310fd869f4f49d872d5163f5db5bb08
parent6b337c5918639adddd7fda40dab7ebe2506783d2 (diff)
download96b-common-035438452f85412438be0f6b4dae88b32353cfac.tar.gz
tty/serial: do not free trasnmit buffer page under port lock
[ Upstream commit d72402145ace0697a6a9e8e75a3de5bf3375f78d ] LKP has hit yet another circular locking dependency between uart console drivers and debugobjects [1]: CPU0 CPU1 rhltable_init() __init_work() debug_object_init uart_shutdown() /* db->lock */ /* uart_port->lock */ debug_print_object() free_page() printk() call_console_drivers() debug_check_no_obj_freed() /* uart_port->lock */ /* db->lock */ debug_print_object() So there are two dependency chains: uart_port->lock -> db->lock And db->lock -> uart_port->lock This particular circular locking dependency can be addressed in several ways: a) One way would be to move debug_print_object() out of db->lock scope and, thus, break the db->lock -> uart_port->lock chain. b) Another one would be to free() transmit buffer page out of db->lock in UART code; which is what this patch does. It makes sense to apply a) and b) independently: there are too many things going on behind free(), none of which depend on uart_port->lock. The patch fixes transmit buffer page free() in uart_shutdown() and, additionally, in uart_port_startup() (as was suggested by Dmitry Safonov). [1] https://lore.kernel.org/lkml/20181211091154.GL23332@shao2-debian/T/#u Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Reviewed-by: Petr Mladek <pmladek@suse.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jslaby@suse.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Waiman Long <longman@redhat.com> Cc: Dmitry Safonov <dima@arista.com> Cc: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
-rw-r--r--drivers/tty/serial/serial_core.c22
1 files changed, 16 insertions, 6 deletions
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 6db8844ef3ec..543d0f95f094 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -218,10 +218,15 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
if (!state->xmit.buf) {
state->xmit.buf = (unsigned char *) page;
uart_circ_clear(&state->xmit);
+ uart_port_unlock(uport, flags);
} else {
+ uart_port_unlock(uport, flags);
+ /*
+ * Do not free() the page under the port lock, see
+ * uart_shutdown().
+ */
free_page(page);
}
- uart_port_unlock(uport, flags);
retval = uport->ops->startup(uport);
if (retval == 0) {
@@ -281,6 +286,7 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
struct uart_port *uport = uart_port_check(state);
struct tty_port *port = &state->port;
unsigned long flags = 0;
+ char *xmit_buf = NULL;
/*
* Set the TTY IO error marker
@@ -311,14 +317,18 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
tty_port_set_suspended(port, 0);
/*
- * Free the transmit buffer page.
+ * Do not free() the transmit buffer page under the port lock since
+ * this can create various circular locking scenarios. For instance,
+ * console driver may need to allocate/free a debug object, which
+ * can endup in printk() recursion.
*/
uart_port_lock(state, flags);
- if (state->xmit.buf) {
- free_page((unsigned long)state->xmit.buf);
- state->xmit.buf = NULL;
- }
+ xmit_buf = state->xmit.buf;
+ state->xmit.buf = NULL;
uart_port_unlock(uport, flags);
+
+ if (xmit_buf)
+ free_page((unsigned long)xmit_buf);
}
/**