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Message-ID: <20251230113357.1299759-1-wale.zhang.ftd@gmail.com>
Date: Tue, 30 Dec 2025 19:33:57 +0800
From: Wale Zhang <wale.zhang.ftd@...il.com>
To: colyli@...as.com
Cc: kent.overstreet@...ux.dev,
linux-bcache@...r.kernel.org,
linux-kernel@...r.kernel.org,
Wale Zhang <wale.zhang.ftd@...il.com>
Subject: [RFC PATCH] bcache: make bcache_is_reboot atomic.
bcache: make bcache_is_reboot atomic.
The smp_mb is mainly used to ensure the dependency relationship between
variables, but there is only one variable bcache_is_reboot. Therefore,
using smp_mb is not very appropriate.
When bcache_reboot and register_bcache occur concurrently, register_bcache
cannot immediately detect that bcache_is_reboot has been set to true.
cpu0 cpu1
bcache_reboot
bcache_is_reboot = true;
smp_mb(); register_bcache
smp_mb();
if (bcache_is_reboot)
// bcache_is_reboot may still be false.
Signed-off-by: Wale Zhang <wale.zhang.ftd@...il.com>
---
drivers/md/bcache/super.c | 19 ++++++-------------
drivers/md/bcache/sysfs.c | 14 +++++++-------
2 files changed, 13 insertions(+), 20 deletions(-)
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index c17d4517af22..0b2098aa7234 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -41,7 +41,7 @@ static const char invalid_uuid[] = {
static struct kobject *bcache_kobj;
struct mutex bch_register_lock;
-bool bcache_is_reboot;
+atomic_t bcache_is_reboot = ATOMIC_INIT(0);
LIST_HEAD(bch_cache_sets);
static LIST_HEAD(uncached_devices);
@@ -2561,10 +2561,8 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
if (!try_module_get(THIS_MODULE))
goto out;
- /* For latest state of bcache_is_reboot */
- smp_mb();
err = "bcache is in reboot";
- if (bcache_is_reboot)
+ if (atomic_read(&bcache_is_reboot))
goto out_module_put;
ret = -ENOMEM;
@@ -2735,7 +2733,7 @@ static ssize_t bch_pending_bdevs_cleanup(struct kobject *k,
static int bcache_reboot(struct notifier_block *n, unsigned long code, void *x)
{
- if (bcache_is_reboot)
+ if (atomic_read(&bcache_is_reboot))
return NOTIFY_DONE;
if (code == SYS_DOWN ||
@@ -2750,16 +2748,11 @@ static int bcache_reboot(struct notifier_block *n, unsigned long code, void *x)
mutex_lock(&bch_register_lock);
- if (bcache_is_reboot)
+ if (atomic_read(&bcache_is_reboot))
goto out;
/* New registration is rejected since now */
- bcache_is_reboot = true;
- /*
- * Make registering caller (if there is) on other CPU
- * core know bcache_is_reboot set to true earlier
- */
- smp_mb();
+ atomic_set(&bcache_is_reboot, 1);
if (list_empty(&bch_cache_sets) &&
list_empty(&uncached_devices))
@@ -2935,7 +2928,7 @@ static int __init bcache_init(void)
bch_debug_init();
- bcache_is_reboot = false;
+ atomic_set(&bcache_is_reboot, 0);
return 0;
err:
diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index 72f38e5b6f5c..5384653c5bbb 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -17,7 +17,7 @@
#include <linux/sort.h>
#include <linux/sched/clock.h>
-extern bool bcache_is_reboot;
+extern atomic_t bcache_is_reboot;
/* Default is 0 ("writethrough") */
static const char * const bch_cache_modes[] = {
@@ -296,7 +296,7 @@ STORE(__cached_dev)
struct kobj_uevent_env *env;
/* no user space access if system is rebooting */
- if (bcache_is_reboot)
+ if (atomic_read(&bcache_is_reboot))
return -EBUSY;
#define d_strtoul(var) sysfs_strtoul(var, dc->var)
@@ -459,7 +459,7 @@ STORE(bch_cached_dev)
disk.kobj);
/* no user space access if system is rebooting */
- if (bcache_is_reboot)
+ if (atomic_read(&bcache_is_reboot))
return -EBUSY;
mutex_lock(&bch_register_lock);
@@ -571,7 +571,7 @@ STORE(__bch_flash_dev)
struct uuid_entry *u = &d->c->uuids[d->id];
/* no user space access if system is rebooting */
- if (bcache_is_reboot)
+ if (atomic_read(&bcache_is_reboot))
return -EBUSY;
sysfs_strtoul(data_csum, d->data_csum);
@@ -814,7 +814,7 @@ STORE(__bch_cache_set)
ssize_t v;
/* no user space access if system is rebooting */
- if (bcache_is_reboot)
+ if (atomic_read(&bcache_is_reboot))
return -EBUSY;
if (attr == &sysfs_unregister)
@@ -941,7 +941,7 @@ STORE(bch_cache_set_internal)
struct cache_set *c = container_of(kobj, struct cache_set, internal);
/* no user space access if system is rebooting */
- if (bcache_is_reboot)
+ if (atomic_read(&bcache_is_reboot))
return -EBUSY;
return bch_cache_set_store(&c->kobj, attr, buf, size);
@@ -1137,7 +1137,7 @@ STORE(__bch_cache)
ssize_t v;
/* no user space access if system is rebooting */
- if (bcache_is_reboot)
+ if (atomic_read(&bcache_is_reboot))
return -EBUSY;
if (attr == &sysfs_cache_replacement_policy) {
--
2.43.0
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