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0a5d2efa38
The main purpose of the test is to demonstrate the lock problem for the free of bpf_timer under PREEMPT_RT. When freeing a bpf_timer which is running on other CPU in bpf_timer_cancel_and_free(), hrtimer_cancel() will try to acquire a spin-lock (namely softirq_expiry_lock), however the freeing procedure has already held a raw-spin-lock. The test first creates two threads: one to start timers and the other to free timers. The start-timers thread will start the timer and then wake up the free-timers thread to free these timers when the starts complete. After freeing, the free-timer thread will wake up the start-timer thread to complete the current iteration. A loop of 10 iterations is used. Signed-off-by: Hou Tao <houtao1@huawei.com> Link: https://lore.kernel.org/r/20250117101816.2101857-6-houtao@huaweicloud.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
71 lines
1.4 KiB
C
71 lines
1.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (C) 2025. Huawei Technologies Co., Ltd */
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#include <linux/bpf.h>
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#include <time.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_helpers.h>
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#define MAX_ENTRIES 8
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struct map_value {
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struct bpf_timer timer;
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};
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struct {
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__uint(type, BPF_MAP_TYPE_HASH);
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__type(key, int);
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__type(value, struct map_value);
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__uint(max_entries, MAX_ENTRIES);
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} map SEC(".maps");
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static int timer_cb(void *map, void *key, struct map_value *value)
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{
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volatile int sum = 0;
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int i;
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bpf_for(i, 0, 1024 * 1024) sum += i;
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return 0;
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}
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static int start_cb(int key)
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{
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struct map_value *value;
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value = bpf_map_lookup_elem(&map, (void *)&key);
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if (!value)
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return 0;
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bpf_timer_init(&value->timer, &map, CLOCK_MONOTONIC);
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bpf_timer_set_callback(&value->timer, timer_cb);
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/* Hope 100us will be enough to wake-up and run the overwrite thread */
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bpf_timer_start(&value->timer, 100000, BPF_F_TIMER_CPU_PIN);
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return 0;
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}
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static int overwrite_cb(int key)
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{
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struct map_value zero = {};
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/* Free the timer which may run on other CPU */
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bpf_map_update_elem(&map, (void *)&key, &zero, BPF_ANY);
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return 0;
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}
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SEC("syscall")
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int BPF_PROG(start_timer)
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{
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bpf_loop(MAX_ENTRIES, start_cb, NULL, 0);
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return 0;
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}
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SEC("syscall")
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int BPF_PROG(overwrite_timer)
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{
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bpf_loop(MAX_ENTRIES, overwrite_cb, NULL, 0);
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return 0;
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}
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char _license[] SEC("license") = "GPL";
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