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From: John Ogness <john.ogness@linutronix.de>
Date: Wed, 24 Apr 2019 16:36:04 +0200
Subject: [PATCH] printk: kmsg_dump: remove mutex usage
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.0/older/patches-5.0.10-rt7.tar.xz
The kmsg dumper can be called from any context, but the dumping
helpers were using a mutex to synchronize the iterator against
concurrent dumps.
Rather than trying to synchronize the iterator, use a local copy
of the iterator during the dump. Then no synchronization is
required.
Reported-by: Scott Wood <swood@redhat.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/printk/printk.c | 23 ++++++++++-------------
1 file changed, 10 insertions(+), 13 deletions(-)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -359,8 +359,6 @@ static u64 syslog_seq;
static size_t syslog_partial;
static bool syslog_time;
-static DEFINE_MUTEX(kmsg_dump_lock);
-
/* the last printk record at the last 'clear' command */
static u64 clear_seq;
@@ -2820,6 +2818,7 @@ module_param_named(always_kmsg_dump, alw
*/
void kmsg_dump(enum kmsg_dump_reason reason)
{
+ struct kmsg_dumper dumper_local;
struct kmsg_dumper *dumper;
if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)
@@ -2830,16 +2829,18 @@ void kmsg_dump(enum kmsg_dump_reason rea
if (dumper->max_reason && reason > dumper->max_reason)
continue;
- /* initialize iterator with data about the stored records */
- dumper->active = true;
+ /*
+ * use a local copy to avoid modifying the
+ * iterator used by any other cpus/contexts
+ */
+ memcpy(&dumper_local, dumper, sizeof(dumper_local));
- kmsg_dump_rewind(dumper);
+ /* initialize iterator with data about the stored records */
+ dumper_local.active = true;
+ kmsg_dump_rewind(&dumper_local);
/* invoke dumper which will iterate over records */
- dumper->dump(dumper, reason);
-
- /* reset iterator */
- dumper->active = false;
+ dumper_local.dump(&dumper_local, reason);
}
rcu_read_unlock();
}
@@ -2951,9 +2952,7 @@ bool kmsg_dump_get_line(struct kmsg_dump
{
bool ret;
- mutex_lock(&kmsg_dump_lock);
ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
- mutex_unlock(&kmsg_dump_lock);
return ret;
}
@@ -3105,9 +3104,7 @@ void kmsg_dump_rewind_nolock(struct kmsg
*/
void kmsg_dump_rewind(struct kmsg_dumper *dumper)
{
- mutex_lock(&kmsg_dump_lock);
kmsg_dump_rewind_nolock(dumper);
- mutex_unlock(&kmsg_dump_lock);
}
EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
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