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Now that kmalloc can be used from NMI context via kmalloc_nolock(), migrate BPF internal allocations away from bpf_mem_alloc to use the standard slab allocator. Use kfree_rcu() for deferred freeing, which guarantees both tasks trace and normal RCU grace periods before the memory is reclaimed. Patch 1 migrates bpf_task_work_ctx from bpf_mem_alloc/bpf_mem_free to kmalloc_nolock/kfree_rcu. Patch 2 migrates bpf_dynptr_file_impl from bpf_mem_alloc/bpf_mem_free to kmalloc_nolock/kfree_rcu. Signed-off-by: Mykyta Yatsenko <[email protected]> --- b4-submit-tracking --- # This section is used internally by b4 prep for tracking purposes. { "series": { "revision": 1, "change-id": "20260223-kmalloc_special-933ec4c543d7", "prefixes": [] } }
Now that kmalloc can be used from NMI context, replace bpf_mem_alloc/ bpf_mem_free with kmalloc_nolock/kfree_rcu for bpf_task_work_ctx. bpf_task_work_ctx_reset() releases prog and task references while refcount is zero, before kfree_rcu() defers the actual free. Sleepable BPF programs (e.g. BPF_PROG_TYPE_SYSCALL) hold rcu_read_lock_trace but not regular rcu_read_lock. Since kfree_rcu waits for a regular RCU grace period, the ctx memory can be freed while a sleepable program is still running. Add explicit rcu_read_lock/unlock around the pointer read and refcount tryget in bpf_task_work_acquire_ctx to close this race window. For the lost-cmpxchg path the ctx was never published, so plain kfree is safe.
Replace bpf_mem_alloc/bpf_mem_free with kmalloc_nolock/kfree_rcu for bpf_dynptr_file_impl, continuing the migration away from bpf_mem_alloc now that kmalloc can be used from NMI context. freader_cleanup() runs before kfree_rcu() while the dynptr still holds exclusive access. kfree_rcu() then defers the actual free until after a grace period. Add struct rcu_head to bpf_dynptr_file_impl for kfree_rcu().
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