Commit fda64ae0 authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Alexei Starovoitov
Browse files

bpf: bpf_task_storage_delete_recur does lookup first before the deadlock check 



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: default avatarMartin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20221025184524.3526117-7-martin.lau@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 4279adb0

kernel/bpf/bpf_task_storage.c

+11 −7
Original line number Diff line number Diff line
@@ -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);
@@ -289,20 +293,20 @@ 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);

	ret = task_storage_delete(task, map, nobusy);

	if (nobusy)

		bpf_task_storage_unlock();

	return ret;

}