From: John Stultz <jstultz@xxxxxxxxxx>
[ Upstream commit 76d62f24db07f22ccf9bc18ca793c27d4ebef721 ]
Wei Wang reported seeing priority inversion caused latencies
caused by contention on pmsg_lock, and suggested it be switched
to a rt_mutex.
I was initially hesitant this would help, as the tasks in that
trace all seemed to be SCHED_NORMAL, so the benefit would be
limited to only nice boosting.
However, another similar issue was raised where the priority
inversion was seen did involve a blocked RT task so it is clear
this would be helpful in that case.
Cc: Wei Wang <wvw@xxxxxxxxxx>
Cc: Midas Chien<midaschieh@xxxxxxxxxx>
Cc: Connor O'Brien <connoro@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Anton Vorontsov <anton@xxxxxxxxxx>
Cc: Colin Cross <ccross@xxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: kernel-team@xxxxxxxxxxx
Fixes: 9d5438f462ab ("pstore: Add pmsg - user-space accessible pstore object")
Reported-by: Wei Wang <wvw@xxxxxxxxxx>
Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20221214231834.3711880-1-jstultz@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/pstore/pmsg.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/fs/pstore/pmsg.c b/fs/pstore/pmsg.c
index d8542ec2f38c..18cf94b597e0 100644
--- a/fs/pstore/pmsg.c
+++ b/fs/pstore/pmsg.c
@@ -7,9 +7,10 @@
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
+#include <linux/rtmutex.h>
#include "internal.h"
-static DEFINE_MUTEX(pmsg_lock);
+static DEFINE_RT_MUTEX(pmsg_lock);
static ssize_t write_pmsg(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
@@ -28,9 +29,9 @@ static ssize_t write_pmsg(struct file *file, const char __user *buf,
if (!access_ok(buf, count))
return -EFAULT;
- mutex_lock(&pmsg_lock);
+ rt_mutex_lock(&pmsg_lock);
ret = psinfo->write_user(&record, buf);
- mutex_unlock(&pmsg_lock);
+ rt_mutex_unlock(&pmsg_lock);
return ret ? ret : count;
}
--
2.35.1
