| Message ID | 20230306154138.3775-5-findns94@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm, memcg: cgroup v1 and v2 tunable load/store tearing fixes | expand |
On Mon 06-03-23 23:41:38, Yue Zhao wrote: > The knob for cgroup v1 memory controller: memory.soft_limit_in_bytes > is not protected by any locking so it can be modified while it is used. > This is not an actual problem because races are unlikely. > But it is better to use READ_ONCE/WRITE_ONCE to prevent compiler from > doing anything funky. > > The access of memcg->soft_limit is lockless, > so it can be concurrently set at the same time as we are > trying to read it. Similar here. mem_cgroup_css_reset and mem_cgroup_css_alloc are not covered. > > Signed-off-by: Yue Zhao <findns94@gmail.com> > --- > mm/memcontrol.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 26605b2f51b1..20566f59bbcb 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3728,7 +3728,7 @@ static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css, > case RES_FAILCNT: > return counter->failcnt; > case RES_SOFT_LIMIT: > - return (u64)memcg->soft_limit * PAGE_SIZE; > + return (u64)READ_ONCE(memcg->soft_limit) * PAGE_SIZE; > default: > BUG(); > } > @@ -3870,7 +3870,7 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of, > if (IS_ENABLED(CONFIG_PREEMPT_RT)) { > ret = -EOPNOTSUPP; > } else { > - memcg->soft_limit = nr_pages; > + WRITE_ONCE(memcg->soft_limit, nr_pages); > ret = 0; > } > break; > -- > 2.17.1
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 26605b2f51b1..20566f59bbcb 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3728,7 +3728,7 @@ static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css, case RES_FAILCNT: return counter->failcnt; case RES_SOFT_LIMIT: - return (u64)memcg->soft_limit * PAGE_SIZE; + return (u64)READ_ONCE(memcg->soft_limit) * PAGE_SIZE; default: BUG(); } @@ -3870,7 +3870,7 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of, if (IS_ENABLED(CONFIG_PREEMPT_RT)) { ret = -EOPNOTSUPP; } else { - memcg->soft_limit = nr_pages; + WRITE_ONCE(memcg->soft_limit, nr_pages); ret = 0; } break;
The knob for cgroup v1 memory controller: memory.soft_limit_in_bytes is not protected by any locking so it can be modified while it is used. This is not an actual problem because races are unlikely. But it is better to use READ_ONCE/WRITE_ONCE to prevent compiler from doing anything funky. The access of memcg->soft_limit is lockless, so it can be concurrently set at the same time as we are trying to read it. Signed-off-by: Yue Zhao <findns94@gmail.com> --- mm/memcontrol.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)