On 2023/2/26 00:17, Kirill Tkhai wrote:
On 25.02.2023 18:57, Qi Zheng wrote:
<...>
How about this?
diff --git a/mm/vmscan.c b/mm/vmscan.c
index ffddbd204259..9d8c53075298 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1012,7 +1012,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
int priority)
{
unsigned long ret, freed = 0;
- struct shrinker *shrinker;
+ struct shrinker *shrinker = NULL;
int srcu_idx, generation;
/*
@@ -1025,11 +1025,15 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg))
return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
+again:
srcu_idx = srcu_read_lock(&shrinker_srcu);
generation = atomic_read(&shrinker_srcu_generation);
- list_for_each_entry_srcu(shrinker, &shrinker_list, list,
- srcu_read_lock_held(&shrinker_srcu)) {
+ if (!shrinker)
+ shrinker = list_entry_rcu(shrinker_list.next, struct shrinker, list);
+ else
+ shrinker = list_entry_rcu(shrinker->list.next, struct shrinker, list);
+ list_for_each_entry_from_rcu(shrinker, &shrinker_list, list) {
struct shrink_control sc = {
.gfp_mask = gfp_mask,
.nid = nid,
@@ -1042,8 +1046,9 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
freed += ret;
if (atomic_read(&shrinker_srcu_generation) != generation) {
- freed = freed ? : 1;
- break;
+ srcu_read_unlock(&shrinker_srcu, srcu_idx);
After SRCU in unlocked we can't believe @shrinker anymore. So, above list_entry_rcu(shrinker->list.next)
dereferences some random memory.
Indeed.
+ cond_resched();
+ goto again;
}
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 27ef9946ae8a..0b197bba1257 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -204,6 +204,7 @@ static void set_task_reclaim_state(struct task_struct *task,
LIST_HEAD(shrinker_list);
DEFINE_MUTEX(shrinker_mutex);
DEFINE_SRCU(shrinker_srcu);
+static atomic_t shrinker_srcu_generation = ATOMIC_INIT(0);
#ifdef CONFIG_MEMCG
static int shrinker_nr_max;
@@ -782,6 +783,7 @@ void unregister_shrinker(struct shrinker *shrinker)
debugfs_entry = shrinker_debugfs_remove(shrinker);
mutex_unlock(&shrinker_mutex);
+ atomic_inc(&shrinker_srcu_generation);
synchronize_srcu(&shrinker_srcu);
debugfs_remove_recursive(debugfs_entry);
@@ -799,6 +801,7 @@ EXPORT_SYMBOL(unregister_shrinker);
*/
void synchronize_shrinkers(void)
{
+ atomic_inc(&shrinker_srcu_generation);
synchronize_srcu(&shrinker_srcu);
}
EXPORT_SYMBOL(synchronize_shrinkers);
@@ -908,18 +911,19 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
{
struct shrinker_info *info;
unsigned long ret, freed = 0;
- int srcu_idx;
- int i;
+ int srcu_idx, generation;
+ int i = 0;
if (!mem_cgroup_online(memcg))
return 0;
-
+again:
srcu_idx = srcu_read_lock(&shrinker_srcu);
info = shrinker_info_srcu(memcg, nid);
if (unlikely(!info))
goto unlock;
- for_each_set_bit(i, info->map, info->map_nr_max) {
+ generation = atomic_read(&shrinker_srcu_generation);
+ for_each_set_bit_from(i, info->map, info->map_nr_max) {
struct shrink_control sc = {
.gfp_mask = gfp_mask,
.nid = nid,
@@ -965,6 +969,11 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
set_shrinker_bit(memcg, nid, i);
}
freed += ret;
+
+ if (atomic_read(&shrinker_srcu_generation) != generation) {
+ srcu_read_unlock(&shrinker_srcu, srcu_idx);
Maybe we can add the following code here, so as to avoid repeating the
current id and avoid triggering softlockup:
i++;
This is OK.
cond_resched();
Possible, existing cond_resched() in do_shrink_slab() is enough.
Yeah.
I will add this patch in the next version. May I mark you as the author
of this patch?
Thanks,
Qi
And this. :)
Thanks,
Qi
Thanks,
Qi
+ goto again;
+ }
}
unlock:
srcu_read_unlock(&shrinker_srcu, srcu_idx);
@@ -1004,7 +1013,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
{
unsigned long ret, freed = 0;
struct shrinker *shrinker;
- int srcu_idx;
+ int srcu_idx, generation;
/*
* The root memcg might be allocated even though memcg is disabled
@@ -1017,6 +1026,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
srcu_idx = srcu_read_lock(&shrinker_srcu);
+ generation = atomic_read(&shrinker_srcu_generation);
list_for_each_entry_srcu(shrinker, &shrinker_list, list,
srcu_read_lock_held(&shrinker_srcu)) {
@@ -1030,6 +1040,11 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
if (ret == SHRINK_EMPTY)
ret = 0;
freed += ret;
+
+ if (atomic_read(&shrinker_srcu_generation) != generation) {
+ freed = freed ? : 1;
+ break;
+ }
}
srcu_read_unlock(&shrinker_srcu, srcu_idx);
--
Thanks,
Qi
