Commit d247049f authored by Hou Tao's avatar Hou Tao Committed by Alexei Starovoitov
Browse files

bpf: Only allow sleepable program for resched-able iterator 



When a sleepable program is attached to a hash map iterator, might_fault()
will report "BUG: sleeping function called from invalid context..." if
CONFIG_DEBUG_ATOMIC_SLEEP is enabled. The reason is that rcu_read_lock()
is held in bpf_hash_map_seq_next() and won't be released until all elements
are traversed or bpf_hash_map_seq_stop() is called.

Fixing it by reusing BPF_ITER_RESCHED to indicate that only non-sleepable
program is allowed for iterator without BPF_ITER_RESCHED. We can revise
bpf_iter_link_attach() later if there are other conditions which may
cause rcu_read_lock() or spin_lock() issues.

Signed-off-by: default avatarHou Tao <houtao1@huawei.com>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220810080538.1845898-7-houtao@huaweicloud.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 52bd05eb

kernel/bpf/bpf_iter.c

+10 −1
Original line number Diff line number Diff line
@@ -68,13 +68,18 @@ static void bpf_iter_done_stop(struct seq_file *seq) 
	iter_priv->done_stop = true;

}



static inline bool bpf_iter_target_support_resched(const struct bpf_iter_target_info *tinfo)

{

	return tinfo->reg_info->feature & BPF_ITER_RESCHED;

}



static bool bpf_iter_support_resched(struct seq_file *seq)

{

	struct bpf_iter_priv_data *iter_priv;



	iter_priv = container_of(seq->private, struct bpf_iter_priv_data,

				 target_private);

	return iter_priv->tinfo->reg_info->feature & BPF_ITER_RESCHED;

	return bpf_iter_target_support_resched(iter_priv->tinfo);

}



/* maximum visited objects before bailing out */
@@ -537,6 +542,10 @@ int bpf_iter_link_attach(const union bpf_attr *attr, bpfptr_t uattr, 
	if (!tinfo)

		return -ENOENT;



	/* Only allow sleepable program for resched-able iterator */

	if (prog->aux->sleepable && !bpf_iter_target_support_resched(tinfo))

		return -EINVAL;



	link = kzalloc(sizeof(*link), GFP_USER | __GFP_NOWARN);

	if (!link)

		return -ENOMEM;