From: John Stultz jstultz@google.com
[ 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@google.com Cc: Midas Chienmidaschieh@google.com Cc: Connor O'Brien connoro@google.com Cc: Kees Cook keescook@chromium.org Cc: Anton Vorontsov anton@enomsg.org Cc: Colin Cross ccross@android.com Cc: Tony Luck tony.luck@intel.com Cc: kernel-team@android.com Fixes: 9d5438f462ab ("pstore: Add pmsg - user-space accessible pstore object") Reported-by: Wei Wang wvw@google.com Signed-off-by: John Stultz jstultz@google.com Signed-off-by: Kees Cook keescook@chromium.org Link: https://lore.kernel.org/r/20221214231834.3711880-1-jstultz@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 24db02de1787..ffc13ea196d2 100644 --- a/fs/pstore/pmsg.c +++ b/fs/pstore/pmsg.c @@ -15,9 +15,10 @@ #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) @@ -36,9 +37,9 @@ static ssize_t write_pmsg(struct file *file, const char __user *buf, if (!access_ok(VERIFY_READ, 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; }