LinuxLists.cc - [PATCH] mm: memcg: add NULL check to obj_cgroup

2024-03-16 01:58:17

Subject: [PATCH] mm: memcg: add NULL check to obj_cgroup_put()

9 out of 16 callers perform a NULL check before calling
obj_cgroup_put(). Move the NULL check in the function, similar to
mem_cgroup_put(). The unlikely() NULL check in current_objcg_update()
was left alone to avoid dropping the unlikey() annotation as this a fast
path.

Signed-off-by: Yosry Ahmed <[email protected]>
---
include/linux/memcontrol.h | 3 ++-
kernel/bpf/memalloc.c | 6 ++----
mm/memcontrol.c | 18 ++++++------------
mm/zswap.c | 3 +--
4 files changed, 11 insertions(+), 19 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 394fd0a887ae7..b6264796815d4 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -818,7 +818,8 @@ static inline void obj_cgroup_get_many(struct obj_cgroup *objcg,

static inline void obj_cgroup_put(struct obj_cgroup *objcg)
{
- percpu_ref_put(&objcg->refcnt);
+ if (objcg)
+ percpu_ref_put(&objcg->refcnt);
}

static inline bool mem_cgroup_tryget(struct mem_cgroup *memcg)
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 550f02e2cb132..a546aba46d5da 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -759,8 +759,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
}
- if (ma->objcg)
- obj_cgroup_put(ma->objcg);
+ obj_cgroup_put(ma->objcg);
destroy_mem_alloc(ma, rcu_in_progress);
}
if (ma->caches) {
@@ -776,8 +775,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
}
}
- if (ma->objcg)
- obj_cgroup_put(ma->objcg);
+ obj_cgroup_put(ma->objcg);
destroy_mem_alloc(ma, rcu_in_progress);
}
}
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 138bcfa182344..aab3f5473203a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2370,8 +2370,7 @@ static void drain_local_stock(struct work_struct *dummy)
clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);

local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
- if (old)
- obj_cgroup_put(old);
+ obj_cgroup_put(old);
}

/*
@@ -3147,8 +3146,7 @@ static struct obj_cgroup *current_objcg_update(void)
if (old) {
old = (struct obj_cgroup *)
((unsigned long)old & ~CURRENT_OBJCG_UPDATE_FLAG);
- if (old)
- obj_cgroup_put(old);
+ obj_cgroup_put(old);

old = NULL;
}
@@ -3420,8 +3418,7 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
mod_objcg_mlstate(objcg, pgdat, idx, nr);

local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
- if (old)
- obj_cgroup_put(old);
+ obj_cgroup_put(old);
}

static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes)
@@ -3548,8 +3545,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes,
}

local_unlock_irqrestore(&memcg_stock.stock_lock, flags);
- if (old)
- obj_cgroup_put(old);
+ obj_cgroup_put(old);

if (nr_pages)
obj_cgroup_uncharge_pages(objcg, nr_pages);
@@ -5470,8 +5466,7 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
{
int node;

- if (memcg->orig_objcg)
- obj_cgroup_put(memcg->orig_objcg);
+ obj_cgroup_put(memcg->orig_objcg);

for_each_node(node)
free_mem_cgroup_per_node_info(memcg, node);
@@ -6622,8 +6617,7 @@ static void mem_cgroup_exit(struct task_struct *task)

objcg = (struct obj_cgroup *)
((unsigned long)objcg & ~CURRENT_OBJCG_UPDATE_FLAG);
- if (objcg)
- obj_cgroup_put(objcg);
+ obj_cgroup_put(objcg);

/*
* Some kernel allocations can happen after this point,
diff --git a/mm/zswap.c b/mm/zswap.c
index e0ec91995f4e3..3c2f960a789ba 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1533,8 +1533,7 @@ bool zswap_store(struct folio *folio)
freepage:
zswap_entry_cache_free(entry);
reject:
- if (objcg)
- obj_cgroup_put(objcg);
+ obj_cgroup_put(objcg);
check_old:
/*
* If the zswap store fails or zswap is disabled, we must invalidate the
--
2.44.0.291.gc1ea87d7ee-goog

2024-03-16 13:00:10

by Johannes Weiner

[permalink] [raw]

Subject: Re: [PATCH] mm: memcg: add NULL check to obj_cgroup_put()

On Sat, Mar 16, 2024 at 01:58:03AM +0000, Yosry Ahmed wrote:
> 9 out of 16 callers perform a NULL check before calling
> obj_cgroup_put(). Move the NULL check in the function, similar to
> mem_cgroup_put(). The unlikely() NULL check in current_objcg_update()
> was left alone to avoid dropping the unlikey() annotation as this a fast
> path.
>
> Signed-off-by: Yosry Ahmed <[email protected]>

Acked-by: Johannes Weiner <[email protected]>

2024-03-16 21:10:31

by Roman Gushchin

[permalink] [raw]