This is a note to let you know that I've just added the patch titled pstore: Switch pmsg_lock to an rt_mutex to avoid priority inversion to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: pstore-switch-pmsg_lock-to-an-rt_mutex-to-avoid-prio.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 6c615333ce4781c582eb6d5fda3b4533ed132658 Author: John Stultz <jstultz@xxxxxxxxxx> Date: Wed Dec 14 23:18:34 2022 +0000 pstore: Switch pmsg_lock to an rt_mutex to avoid priority inversion [ 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> 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; }