From 76d62f24db07f22ccf9bc18ca793c27d4ebef721 Mon Sep 17 00:00:00 2001 From: John Stultz Date: Wed, 14 Dec 2022 23:18:34 +0000 Subject: [PATCH] pstore: Switch pmsg_lock to an rt_mutex to avoid priority inversion 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 Cc: Midas Chien Cc: Connor O'Brien Cc: Kees Cook Cc: Anton Vorontsov Cc: Colin Cross Cc: Tony Luck Cc: kernel-team@android.com Fixes: 9d5438f462ab ("pstore: Add pmsg - user-space accessible pstore object") Reported-by: Wei Wang Signed-off-by: John Stultz Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20221214231834.3711880-1-jstultz@google.com --- 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 d8542ec..18cf94b 100644 --- a/fs/pstore/pmsg.c +++ b/fs/pstore/pmsg.c @@ -7,9 +7,10 @@ #include #include #include +#include #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; } -- 2.7.4