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

John Ogness
2021-02-25T20:24:45Z

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@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
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