bpf: Avoid RCU context warning when unpinning htab with internal structs #6090
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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 <[email protected]> Closes: https://lore.kernel.org/all/[email protected]/ Fixes: 6813466 ("bpf: Add map side support for bpf timers.") Suggested-by: Alexei Starovoitov <[email protected]> Signed-off-by: KaFai Wan <[email protected]>
Add test to verify that unpinning hash tables containing internal timer structures does not trigger context warnings. Each subtest (timer_prealloc and timer_no_prealloc) can trigger the context warning when unpinning, but the warning cannot be triggered twice within a short time interval (a HZ), which is expected behavior. Signed-off-by: KaFai Wan <[email protected]>
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Pull request for series with
subject: bpf: Avoid RCU context warning when unpinning htab with internal structs
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1008205