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-rw-r--r--mm/ksm.c55
1 files changed, 41 insertions, 14 deletions
diff --git a/mm/ksm.c b/mm/ksm.c
index 91f07d0e9ce7..5ea0f64b8714 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -226,7 +226,9 @@ static unsigned int ksm_merge_across_nodes = 1;
#define KSM_RUN_STOP 0
#define KSM_RUN_MERGE 1
#define KSM_RUN_UNMERGE 2
-static unsigned int ksm_run = KSM_RUN_STOP;
+#define KSM_RUN_OFFLINE 4
+static unsigned long ksm_run = KSM_RUN_STOP;
+static void wait_while_offlining(void);
static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
static DEFINE_MUTEX(ksm_thread_mutex);
@@ -1700,6 +1702,7 @@ static int ksm_scan_thread(void *nothing)
while (!kthread_should_stop()) {
mutex_lock(&ksm_thread_mutex);
+ wait_while_offlining();
if (ksmd_should_run())
ksm_do_scan(ksm_thread_pages_to_scan);
mutex_unlock(&ksm_thread_mutex);
@@ -2056,6 +2059,22 @@ void ksm_migrate_page(struct page *newpage, struct page *oldpage)
#endif /* CONFIG_MIGRATION */
#ifdef CONFIG_MEMORY_HOTREMOVE
+static int just_wait(void *word)
+{
+ schedule();
+ return 0;
+}
+
+static void wait_while_offlining(void)
+{
+ while (ksm_run & KSM_RUN_OFFLINE) {
+ mutex_unlock(&ksm_thread_mutex);
+ wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
+ just_wait, TASK_UNINTERRUPTIBLE);
+ mutex_lock(&ksm_thread_mutex);
+ }
+}
+
static void ksm_check_stable_tree(unsigned long start_pfn,
unsigned long end_pfn)
{
@@ -2098,15 +2117,15 @@ static int ksm_memory_callback(struct notifier_block *self,
switch (action) {
case MEM_GOING_OFFLINE:
/*
- * Keep it very simple for now: just lock out ksmd and
- * MADV_UNMERGEABLE while any memory is going offline.
- * mutex_lock_nested() is necessary because lockdep was alarmed
- * that here we take ksm_thread_mutex inside notifier chain
- * mutex, and later take notifier chain mutex inside
- * ksm_thread_mutex to unlock it. But that's safe because both
- * are inside mem_hotplug_mutex.
+ * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
+ * and remove_all_stable_nodes() while memory is going offline:
+ * it is unsafe for them to touch the stable tree at this time.
+ * But unmerge_ksm_pages(), rmap lookups and other entry points
+ * which do not need the ksm_thread_mutex are all safe.
*/
- mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
+ mutex_lock(&ksm_thread_mutex);
+ ksm_run |= KSM_RUN_OFFLINE;
+ mutex_unlock(&ksm_thread_mutex);
break;
case MEM_OFFLINE:
@@ -2122,11 +2141,20 @@ static int ksm_memory_callback(struct notifier_block *self,
/* fallthrough */
case MEM_CANCEL_OFFLINE:
+ mutex_lock(&ksm_thread_mutex);
+ ksm_run &= ~KSM_RUN_OFFLINE;
mutex_unlock(&ksm_thread_mutex);
+
+ smp_mb(); /* wake_up_bit advises this */
+ wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
break;
}
return NOTIFY_OK;
}
+#else
+static void wait_while_offlining(void)
+{
+}
#endif /* CONFIG_MEMORY_HOTREMOVE */
#ifdef CONFIG_SYSFS
@@ -2189,7 +2217,7 @@ KSM_ATTR(pages_to_scan);
static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
char *buf)
{
- return sprintf(buf, "%u\n", ksm_run);
+ return sprintf(buf, "%lu\n", ksm_run);
}
static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
@@ -2212,6 +2240,7 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
*/
mutex_lock(&ksm_thread_mutex);
+ wait_while_offlining();
if (ksm_run != flags) {
ksm_run = flags;
if (flags & KSM_RUN_UNMERGE) {
@@ -2254,6 +2283,7 @@ static ssize_t merge_across_nodes_store(struct kobject *kobj,
return -EINVAL;
mutex_lock(&ksm_thread_mutex);
+ wait_while_offlining();
if (ksm_merge_across_nodes != knob) {
if (ksm_pages_shared || remove_all_stable_nodes())
err = -EBUSY;
@@ -2366,10 +2396,7 @@ static int __init ksm_init(void)
#endif /* CONFIG_SYSFS */
#ifdef CONFIG_MEMORY_HOTREMOVE
- /*
- * Choose a high priority since the callback takes ksm_thread_mutex:
- * later callbacks could only be taking locks which nest within that.
- */
+ /* There is no significance to this priority 100 */
hotplug_memory_notifier(ksm_memory_callback, 100);
#endif
return 0;