[PATCH next v3 01/15] um: synchronize kmsg_dumper

[John Ogness]

The kmsg_dumper can be called from any context and CPU, possibly
from multiple CPUs simultaneously. Since a static buffer is used
to retrieve the kernel logs, this buffer must be protected against
simultaneous dumping. Skip dumping if another context is already
dumping.

Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
---
 arch/um/kernel/kmsg_dump.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index 6516ef1f8274..4869e2cc787c 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/kmsg_dump.h>
+#include <linux/spinlock.h>
 #include <linux/console.h>
 #include <linux/string.h>
 #include <shared/init.h>
@@ -9,6 +10,7 @@
 static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 				enum kmsg_dump_reason reason)
 {
+	static DEFINE_SPINLOCK(lock);
 	static char line[1024];
 	struct console *con;
 	size_t len = 0;
@@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 	if (con)
 		return;
 
+	if (!spin_trylock(&lock))
+		return;
+
 	printf("kmsg_dump:\n");
 	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
+
+	spin_unlock(&lock);
 }
 
 static struct kmsg_dumper kmsg_dumper = {
-- 
2.20.1