[PATCH v2] x86/microcode: Remove microcode_mutex.

From: Sebastian Andrzej Siewior
Date: Fri Aug 04 2023 - 03:59:02 EST


microcode_mutex is only used by reload_store(). It has a comment saying
"to synchronize with each other". Other user of this mutex have been
removed in the commits
181b6f40e9ea8 ("x86/microcode: Rip out the OLD_INTERFACE").
b6f86689d5b74 ("x86/microcode: Rip out the subsys interface gunk")

The sysfs interface does not need additional synchronisation vs itself
because it is provided as kernfs_ops::mutex which is acquired in
kernfs_fop_write_iter().

Remove superfluous microcode_mutex.

Link: https://lore.kernel.org/r/20230803083253.VGMnC9Gd@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---

v1…v2:
- Add another commit to the commit description which removed another
user. Suggested by Sohil Mehta.
- Also update the comment in microcode_check(). Suggested by Sohil
Mehta.

arch/x86/kernel/cpu/common.c | 3 +--
arch/x86/kernel/cpu/microcode/core.c | 6 ------
2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 0ba1067f4e5f1..de49b9cd8077a 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2276,8 +2276,7 @@ void store_cpu_caps(struct cpuinfo_x86 *curr_info)
* @prev_info: CPU capabilities stored before an update.
*
* The microcode loader calls this upon late microcode load to recheck features,
- * only when microcode has been updated. Caller holds microcode_mutex and CPU
- * hotplug lock.
+ * only when microcode has been updated. Caller holds and CPU hotplug lock.
*
* Return: None
*/
diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 3afcf3de0dd49..2f9d35744bc41 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -54,15 +54,12 @@ LIST_HEAD(microcode_cache);
*
* All non cpu-hotplug-callback call sites use:
*
- * - microcode_mutex to synchronize with each other;
* - cpus_read_lock/unlock() to synchronize with
* the cpu-hotplug-callback call sites.
*
* We guarantee that only a single cpu is being
* updated at any particular moment of time.
*/
-static DEFINE_MUTEX(microcode_mutex);
-
struct ucode_cpu_info ucode_cpu_info[NR_CPUS];

struct cpu_info_ctx {
@@ -488,10 +485,7 @@ static ssize_t reload_store(struct device *dev,
if (tmp_ret != UCODE_NEW)
goto put;

- mutex_lock(&microcode_mutex);
ret = microcode_reload_late();
- mutex_unlock(&microcode_mutex);
-
put:
cpus_read_unlock();

--
2.40.1