On Thu, Sep 17, 2020 at 12:46 AM Muchun Song <songmuchun@xxxxxxxxxxxxx> wrote:
>
> The in_atomic macro cannot always detect atomic context. In particular,
> it cannot know about held spinlocks in non-preemptible kernels. Although,
> there is no user call bpf_link_put() with holding spinlock now. Be the
> safe side, we can avoid this in the feature.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
This change seems unnecessary (or at least premature), as if we ever
get a use case that does bpf_link_put() from under held spinlock, we
should see a warning about that (and in that case I bet code can be
rewritten to not hold spinlock during bpf_link_put()). But on the
other hand it makes bpf_link_put() to follow the pattern of
bpf_map_put(), which always defers the work, so I'm ok with this. As
Song mentioned, this is not called from a performance-critical hot
path, so doesn't matter all that much.
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
> kernel/bpf/syscall.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 178c147350f5..6347be0a5c82 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2345,12 +2345,8 @@ void bpf_link_put(struct bpf_link *link)
> if (!atomic64_dec_and_test(&link->refcnt))
> return;
>
> - if (in_atomic()) {
> - INIT_WORK(&link->work, bpf_link_put_deferred);
> - schedule_work(&link->work);
> - } else {
> - bpf_link_free(link);
> - }
> + INIT_WORK(&link->work, bpf_link_put_deferred);
> + schedule_work(&link->work);
> }
>
> static int bpf_link_release(struct inode *inode, struct file *filp)
> --
> 2.20.1
>
