[PATCH 5.15 165/276] bpf: Avoid RCU context warning when unpinning htab with internal structs

5.15-stable review patch. If anyone has any objections, please let me know.

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From: KaFai Wan kafai.wan@linux.dev

[ Upstream commit 4f375ade6aa9f37fd72d7a78682f639772089eed ]

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... 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 Link: https://lore.kernel.org/r/20251008102628.808045-2-kafai.wan@linux.dev Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 5a8d9f7467bf4..849df8268af57 100644 --- a/kernel/bpf/inode.c +++ b/kernel/bpf/inode.c @@ -610,7 +610,7 @@ 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;

@@ -625,7 +625,7 @@ static const struct super_operations bpf_super_ops = { .statfs = simple_statfs, .drop_inode = generic_delete_inode, .show_options = bpf_show_options, - .free_inode = bpf_free_inode, + .destroy_inode = bpf_destroy_inode, };

enum {