lkml.org 
[lkml]   [2021]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v4 bpf-next 2/6] bpf: prevent deadlock from recursive bpf_task_storage_[get|delete]
On Mon, Feb 22, 2021 at 5:23 PM Song Liu <songliubraving@fb.com> wrote:
>
> BPF helpers bpf_task_storage_[get|delete] could hold two locks:
> bpf_local_storage_map_bucket->lock and bpf_local_storage->lock. Calling
> these helpers from fentry/fexit programs on functions in bpf_*_storage.c
> may cause deadlock on either locks.
>
> Prevent such deadlock with a per cpu counter, bpf_task_storage_busy, which
> is similar to bpf_prog_active. We need this counter to be global, because
> the two locks here belong to two different objects: bpf_local_storage_map
> and bpf_local_storage. If we pick one of them as the owner of the counter,
> it is still possible to trigger deadlock on the other lock. For example,
> if bpf_local_storage_map owns the counters, it cannot prevent deadlock
> on bpf_local_storage->lock when two maps are used.
>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
> kernel/bpf/bpf_task_storage.c | 57 ++++++++++++++++++++++++++++++-----
> 1 file changed, 50 insertions(+), 7 deletions(-)
>

[...]

> @@ -109,7 +136,9 @@ static void *bpf_pid_task_storage_lookup_elem(struct bpf_map *map, void *key)
> goto out;
> }
>
> + bpf_task_storage_lock();
> sdata = task_storage_lookup(task, map, true);
> + bpf_task_storage_unlock();
> put_pid(pid);
> return sdata ? sdata->data : NULL;
> out:
> @@ -141,8 +170,10 @@ static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key,
> goto out;
> }
>
> + bpf_task_storage_lock();
> sdata = bpf_local_storage_update(
> task, (struct bpf_local_storage_map *)map, value, map_flags);

this should probably be container_of() instead of casting

> + bpf_task_storage_unlock();
>
> err = PTR_ERR_OR_ZERO(sdata);
> out:
> @@ -185,7 +216,9 @@ static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
> goto out;
> }
>
> + bpf_task_storage_lock();
> err = task_storage_delete(task, map);
> + bpf_task_storage_unlock();
> out:
> put_pid(pid);
> return err;

[...]

\
 
 \ /
  Last update: 2021-02-23 07:28    [W:0.093 / U:0.164 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site