[PATCH bpf-next 6/9] bpf: bpf_task_storage_delete_recur does lookup first before the deadlock check

Martin KaFai Lau
2022-10-25T18:46:23Z

Similar to the earlier change in bpf_task_storage_get_recur.
This patch changes bpf_task_storage_delete_recur such that it
does the lookup first. It only returns -EBUSY if it needs to
take the spinlock to do the deletion when potential deadlock
is detected.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
kernel/bpf/bpf_task_storage.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/bpf_task_storage.c b/kernel/bpf/bpf_task_storage.c
index c3a841be438f..f3f79b618a68 100644
--- a/kernel/bpf/bpf_task_storage.c
+++ b/kernel/bpf/bpf_task_storage.c
@@ -184,7 +184,8 @@ static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key,
return err;
}

-static int task_storage_delete(struct task_struct *task, struct bpf_map *map)
+static int task_storage_delete(struct task_struct *task, struct bpf_map *map,
+ bool nobusy)
{
struct bpf_local_storage_data *sdata;

@@ -192,6 +193,9 @@ static int task_storage_delete(struct task_struct *task, struct bpf_map *map)
if (!sdata)
return -ENOENT;

+ if (!nobusy)
+ return -EBUSY;
+
bpf_selem_unlink(SELEM(sdata), true);

return 0;
@@ -220,7 +224,7 @@ static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
}

bpf_task_storage_lock();
- err = task_storage_delete(task, map);
+ err = task_storage_delete(task, map, true);
bpf_task_storage_unlock();
out:
put_pid(pid);
@@ -289,21 +293,21 @@ BPF_CALL_5(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
BPF_CALL_2(bpf_task_storage_delete_recur, struct bpf_map *, map, struct task_struct *,
task)
{
+ bool nobusy;
int ret;

WARN_ON_ONCE(!bpf_rcu_lock_held());
if (!task)
return -EINVAL;

- if (!bpf_task_storage_trylock())
- return -EBUSY;
-
+ nobusy = bpf_task_storage_trylock();
/* This helper must only be called from places where the lifetime of the task
* is guaranteed. Either by being refcounted or by being protected
* by an RCU read-side critical section.
*/
- ret = task_storage_delete(task, map);
- bpf_task_storage_unlock();
+ ret = task_storage_delete(task, map, nobusy);
+ if (nobusy)
+ bpf_task_storage_unlock();
return ret;
}

--
2.30.2