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Message-ID: <20251003084528.502518-2-kafai.wan@linux.dev>
Date: Fri, 3 Oct 2025 16:45:27 +0800
From: KaFai Wan <kafai.wan@...ux.dev>
To: ast@...nel.org,
daniel@...earbox.net,
andrii@...nel.org,
martin.lau@...ux.dev,
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Cc: Le Chen <tom2cat@...u.edu.cn>
Subject: [PATCH bpf 1/2] bpf: Avoid RCU context warning when unpinning htab with internal structs
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() 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@...u.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@...nel.org>
Signed-off-by: KaFai Wan <kafai.wan@...ux.dev>
---
kernel/bpf/inode.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index f90bdcc0a047..65c2a71d7de1 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -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_free_inode,
};
enum {
--
2.43.0
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