[PATCH 5.17 72/75] bpf: Fix usage of trace RCU in local storage.

Greg Kroah-Hartman
2022-06-03T18:13:27Z

From: KP Singh <kpsingh@kernel.org>

commit dcf456c9a095a6e71f53d6f6f004133ee851ee70 upstream.

bpf_{sk,task,inode}_storage_free() do not need to use
call_rcu_tasks_trace as no BPF program should be accessing the owner
as it's being destroyed. The only other reader at this point is
bpf_local_storage_map_free() which uses normal RCU.

The only path that needs trace RCU are:

* bpf_local_storage_{delete,update} helpers
* map_{delete,update}_elem() syscalls

Fixes: 0fe4b381a59e ("bpf: Allow bpf_local_storage to be used by sleepable programs")
Signed-off-by: KP Singh <kpsingh@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220418155158.2865678-1-kpsingh@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/bpf_local_storage.h | 4 ++--
kernel/bpf/bpf_inode_storage.c | 4 ++--
kernel/bpf/bpf_local_storage.c | 29 +++++++++++++++++++----------
kernel/bpf/bpf_task_storage.c | 4 ++--
net/core/bpf_sk_storage.c | 6 +++---
5 files changed, 28 insertions(+), 19 deletions(-)

--- a/include/linux/bpf_local_storage.h
+++ b/include/linux/bpf_local_storage.h
@@ -143,9 +143,9 @@ void bpf_selem_link_storage_nolock(struc

bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
struct bpf_local_storage_elem *selem,
- bool uncharge_omem);
+ bool uncharge_omem, bool use_trace_rcu);

-void bpf_selem_unlink(struct bpf_local_storage_elem *selem);
+void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool use_trace_rcu);

void bpf_selem_link_map(struct bpf_local_storage_map *smap,
struct bpf_local_storage_elem *selem);
--- a/kernel/bpf/bpf_inode_storage.c
+++ b/kernel/bpf/bpf_inode_storage.c
@@ -90,7 +90,7 @@ void bpf_inode_storage_free(struct inode
*/
bpf_selem_unlink_map(selem);
free_inode_storage = bpf_selem_unlink_storage_nolock(
- local_storage, selem, false);
+ local_storage, selem, false, false);
}
raw_spin_unlock_bh(&local_storage->lock);
rcu_read_unlock();
@@ -149,7 +149,7 @@ static int inode_storage_delete(struct i
if (!sdata)
return -ENOENT;

- bpf_selem_unlink(SELEM(sdata));
+ bpf_selem_unlink(SELEM(sdata), true);

return 0;
}
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -106,7 +106,7 @@ static void bpf_selem_free_rcu(struct rc
*/
bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
struct bpf_local_storage_elem *selem,
- bool uncharge_mem)
+ bool uncharge_mem, bool use_trace_rcu)
{
struct bpf_local_storage_map *smap;
bool free_local_storage;
@@ -150,11 +150,16 @@ bool bpf_selem_unlink_storage_nolock(str
SDATA(selem))
RCU_INIT_POINTER(local_storage->cache[smap->cache_idx], NULL);

- call_rcu_tasks_trace(&selem->rcu, bpf_selem_free_rcu);
+ if (use_trace_rcu)
+ call_rcu_tasks_trace(&selem->rcu, bpf_selem_free_rcu);
+ else
+ kfree_rcu(selem, rcu);
+
return free_local_storage;
}

-static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem)
+static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem,
+ bool use_trace_rcu)
{
struct bpf_local_storage *local_storage;
bool free_local_storage = false;
@@ -169,12 +174,16 @@ static void __bpf_selem_unlink_storage(s
raw_spin_lock_irqsave(&local_storage->lock, flags);
if (likely(selem_linked_to_storage(selem)))
free_local_storage = bpf_selem_unlink_storage_nolock(
- local_storage, selem, true);
+ local_storage, selem, true, use_trace_rcu);
raw_spin_unlock_irqrestore(&local_storage->lock, flags);

- if (free_local_storage)
- call_rcu_tasks_trace(&local_storage->rcu,
+ if (free_local_storage) {
+ if (use_trace_rcu)
+ call_rcu_tasks_trace(&local_storage->rcu,
bpf_local_storage_free_rcu);
+ else
+ kfree_rcu(local_storage, rcu);
+ }
}

void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
@@ -214,14 +223,14 @@ void bpf_selem_link_map(struct bpf_local
raw_spin_unlock_irqrestore(&b->lock, flags);
}

-void bpf_selem_unlink(struct bpf_local_storage_elem *selem)
+void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool use_trace_rcu)
{
/* Always unlink from map before unlinking from local_storage
* because selem will be freed after successfully unlinked from
* the local_storage.
*/
bpf_selem_unlink_map(selem);
- __bpf_selem_unlink_storage(selem);
+ __bpf_selem_unlink_storage(selem, use_trace_rcu);
}

struct bpf_local_storage_data *
@@ -454,7 +463,7 @@ bpf_local_storage_update(void *owner, st
if (old_sdata) {
bpf_selem_unlink_map(SELEM(old_sdata));
bpf_selem_unlink_storage_nolock(local_storage, SELEM(old_sdata),
- false);
+ false, true);
}

unlock:
@@ -532,7 +541,7 @@ void bpf_local_storage_map_free(struct b
migrate_disable();
__this_cpu_inc(*busy_counter);
}
- bpf_selem_unlink(selem);
+ bpf_selem_unlink(selem, false);
if (busy_counter) {
__this_cpu_dec(*busy_counter);
migrate_enable();
--- a/kernel/bpf/bpf_task_storage.c
+++ b/kernel/bpf/bpf_task_storage.c
@@ -102,7 +102,7 @@ void bpf_task_storage_free(struct task_s
*/
bpf_selem_unlink_map(selem);
free_task_storage = bpf_selem_unlink_storage_nolock(
- local_storage, selem, false);
+ local_storage, selem, false, false);
}
raw_spin_unlock_irqrestore(&local_storage->lock, flags);
bpf_task_storage_unlock();
@@ -191,7 +191,7 @@ static int task_storage_delete(struct ta
if (!sdata)
return -ENOENT;

- bpf_selem_unlink(SELEM(sdata));
+ bpf_selem_unlink(SELEM(sdata), true);

return 0;
}
--- a/net/core/bpf_sk_storage.c
+++ b/net/core/bpf_sk_storage.c
@@ -40,7 +40,7 @@ static int bpf_sk_storage_del(struct soc
if (!sdata)
return -ENOENT;

- bpf_selem_unlink(SELEM(sdata));
+ bpf_selem_unlink(SELEM(sdata), true);

return 0;
}
@@ -75,8 +75,8 @@ void bpf_sk_storage_free(struct sock *sk
* sk_storage.
*/
bpf_selem_unlink_map(selem);
- free_sk_storage = bpf_selem_unlink_storage_nolock(sk_storage,
- selem, true);
+ free_sk_storage = bpf_selem_unlink_storage_nolock(
+ sk_storage, selem, true, false);
}
raw_spin_unlock_bh(&sk_storage->lock);
rcu_read_unlock();