From b8ef04be6e1935748ef98af98d81b0744cf225d0 Mon Sep 17 00:00:00 2001
From: John Ogness <john.ogness@linutronix.de>
Date: Wed, 16 Nov 2022 17:27:26 +0106
Subject: [PATCH] kdb: use srcu console list iterator
Guarantee safe iteration of the console list by using SRCU.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Aaron Tomlin <atomlin@atomlin.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20221116162152.193147-15-john.ogness@linutronix.de
---
kernel/debug/kdb/kdb_io.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 67d3c48a15222..5c7e9ba7cd6b2 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -545,6 +545,7 @@ static void kdb_msg_write(const char *msg, int msg_len)
{
struct console *c;
const char *cp;
+ int cookie;
int len;
if (msg_len == 0)
@@ -558,8 +559,20 @@ static void kdb_msg_write(const char *msg, int msg_len)
cp++;
}
- for_each_console(c) {
- if (!(c->flags & CON_ENABLED))
+ /*
+ * The console_srcu_read_lock() only provides safe console list
+ * traversal. The use of the ->write() callback relies on all other
+ * CPUs being stopped at the moment and console drivers being able to
+ * handle reentrance when @oops_in_progress is set.
+ *
+ * There is no guarantee that every console driver can handle
+ * reentrance in this way; the developer deploying the debugger
+ * is responsible for ensuring that the console drivers they
+ * have selected handle reentrance appropriately.
+ */
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(c) {
+ if (!(console_srcu_read_flags(c) & CON_ENABLED))
continue;
if (c == dbg_io_ops->cons)
continue;
@@ -577,6 +590,7 @@ static void kdb_msg_write(const char *msg, int msg_len)
--oops_in_progress;
touch_nmi_watchdog();
}
+ console_srcu_read_unlock(cookie);
}
int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
--
2.30.2