[PATCH bpf v3 1/2] bpf: Avoid RCU context warning when unpinning htab with internal structs

KaFai Wan
2025-10-08T10:26:49Z

When unpinning a BPF hash table (htab or htab_lru) that contains internal
structures (timer, workqueue, or task_work) in its values, a BUG warning
is triggered:
BUG: sleeping function called from invalid context at kernel/bpf/hashtab.c:244
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 14, name: ksoftirqd/0
...

The issue arises from the interaction between BPF object unpinning and
RCU callback mechanisms:
1. BPF object unpinning uses ->free_inode() which schedules cleanup via
call_rcu(), deferring the actual freeing to an RCU callback that
executes within the RCU_SOFTIRQ context.
2. During cleanup of hash tables containing internal structures,
htab_map_free_internal_structs() is invoked, which includes
cond_resched() or cond_resched_rcu() calls to yield the CPU during
potentially long operations.

However, cond_resched() or cond_resched_rcu() cannot be safely called from
atomic RCU softirq context, leading to the BUG warning when attempting
to reschedule.

Fix this by changing from ->free_inode() to ->destroy_inode() and rename
bpf_free_inode() to bpf_destroy_inode() for BPF objects (prog, map, link).
This allows direct inode freeing without RCU callback scheduling,
avoiding the invalid context warning.

Reported-by: Le Chen <tom2cat@sjtu.edu.cn>
Closes: https://lore.kernel.org/all/1444123482.1827743.1750996347470.JavaMail.zimbra@sjtu.edu.cn/
Fixes: 68134668c17f ("bpf: Add map side support for bpf timers.")
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: KaFai Wan <kafai.wan@linux.dev>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
---
kernel/bpf/inode.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index f90bdcc0a047..81780bcf8d25 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -775,7 +775,7 @@ static int bpf_show_options(struct seq_file *m, struct dentry *root)
return 0;
}

-static void bpf_free_inode(struct inode *inode)
+static void bpf_destroy_inode(struct inode *inode)
{
enum bpf_type type;

@@ -790,7 +790,7 @@ const struct super_operations bpf_super_ops = {
.statfs = simple_statfs,
.drop_inode = inode_just_drop,
.show_options = bpf_show_options,
- .free_inode = bpf_free_inode,
+ .destroy_inode = bpf_destroy_inode,
};

enum {
--
2.43.0