[PATCH printk-rework 10/14] um: synchronize kmsg_dumper

John Ogness
2021-02-18T09:40:03Z

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.

Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
arch/um/kernel/kmsg_dump.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index f38349ad00ea..173999422ed8 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 <shared/init.h>
#include <shared/kern.h>
@@ -9,8 +10,10 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
enum kmsg_dump_reason reason,
struct kmsg_dumper_iter *iter)
{
+ static DEFINE_SPINLOCK(lock);
static char line[1024];
struct console *con;
+ unsigned long flags;
size_t len = 0;

/* only dump kmsg when no console is available */
@@ -25,11 +28,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
if (con)
return;

+ if (!spin_trylock_irqsave(&lock, flags))
+ return;
+
printf("kmsg_dump:\n");
while (kmsg_dump_get_line(iter, true, line, sizeof(line), &len)) {
line[len] = '\0';
printf("%s", line);
}
+
+ spin_unlock_irqrestore(&lock, flags);
}

static struct kmsg_dumper kmsg_dumper = {
--
2.20.1