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Subject[PATCH printk-rework 09/12] um: synchronize kmsg_dumper
Date
In preparation for removing printk's @logbuf_lock, dumpers that have
assumed to be protected against parallel calls must provide their own
synchronization. Add a locally static spinlock to synchronize the
kmsg_dump call and temporary buffer usage.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
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
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