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: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20221025184524.3526117-7-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/bpf_task_storage.c b/kernel/bpf/bpf_task_storage.c
index c3a841b..f3f79b6 100644 (file)
--- a/kernel/bpf/bpf_task_storage.c
+++ b/kernel/bpf/bpf_task_storage.c
@@ -184,7 +184,8 @@ out:
        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;
 }