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bpf: Use raw_spinlock_t in ringbuf
The function __bpf_ringbuf_reserve is invoked from a tracepoint, which disables preemption. Using spinlock_t in this context can lead to a "sleep in atomic" warning in the RT variant. This issue is illustrated in the example below: BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 556208, name: test_progs preempt_count: 1, expected: 0 RCU nest depth: 1, expected: 1 INFO: lockdep is turned off. Preemption disabled at: [<ffffd33a5c88ea44>] migrate_enable+0xc0/0x39c CPU: 7 PID: 556208 Comm: test_progs Tainted: G Hardware name: Qualcomm SA8775P Ride (DT) Call trace: dump_backtrace+0xac/0x130 show_stack+0x1c/0x30 dump_stack_lvl+0xac/0xe8 dump_stack+0x18/0x30 __might_resched+0x3bc/0x4fc rt_spin_lock+0x8c/0x1a4 __bpf_ringbuf_reserve+0xc4/0x254 bpf_ringbuf_reserve_dynptr+0x5c/0xdc bpf_prog_ac3d15160d62622a_test_read_write+0x104/0x238 trace_call_bpf+0x238/0x774 perf_call_bpf_enter.isra.0+0x104/0x194 perf_syscall_enter+0x2f8/0x510 trace_sys_enter+0x39c/0x564 syscall_trace_enter+0x220/0x3c0 do_el0_svc+0x138/0x1dc el0_svc+0x54/0x130 el0t_64_sync_handler+0x134/0x150 el0t_64_sync+0x17c/0x180 Switch the spinlock to raw_spinlock_t to avoid this error. Fixes: 457f443 ("bpf: Implement BPF ring buffer and verifier support for it") Reported-by: Brian Grech <[email protected]> Signed-off-by: Wander Lairson Costa <[email protected]> Signed-off-by: Wander Lairson Costa <[email protected]> Signed-off-by: Daniel Borkmann <[email protected]> Acked-by: Daniel Borkmann <[email protected]> Link: https://lore.kernel.org/r/[email protected]
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kernel/bpf/ringbuf.c

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -29,7 +29,7 @@ struct bpf_ringbuf {
2929
u64 mask;
3030
struct page **pages;
3131
int nr_pages;
32-
spinlock_t spinlock ____cacheline_aligned_in_smp;
32+
raw_spinlock_t spinlock ____cacheline_aligned_in_smp;
3333
/* For user-space producer ring buffers, an atomic_t busy bit is used
3434
* to synchronize access to the ring buffers in the kernel, rather than
3535
* the spinlock that is used for kernel-producer ring buffers. This is
@@ -173,7 +173,7 @@ static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
173173
if (!rb)
174174
return NULL;
175175

176-
spin_lock_init(&rb->spinlock);
176+
raw_spin_lock_init(&rb->spinlock);
177177
atomic_set(&rb->busy, 0);
178178
init_waitqueue_head(&rb->waitq);
179179
init_irq_work(&rb->work, bpf_ringbuf_notify);
@@ -421,10 +421,10 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
421421
cons_pos = smp_load_acquire(&rb->consumer_pos);
422422

423423
if (in_nmi()) {
424-
if (!spin_trylock_irqsave(&rb->spinlock, flags))
424+
if (!raw_spin_trylock_irqsave(&rb->spinlock, flags))
425425
return NULL;
426426
} else {
427-
spin_lock_irqsave(&rb->spinlock, flags);
427+
raw_spin_lock_irqsave(&rb->spinlock, flags);
428428
}
429429

430430
pend_pos = rb->pending_pos;
@@ -450,7 +450,7 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
450450
*/
451451
if (new_prod_pos - cons_pos > rb->mask ||
452452
new_prod_pos - pend_pos > rb->mask) {
453-
spin_unlock_irqrestore(&rb->spinlock, flags);
453+
raw_spin_unlock_irqrestore(&rb->spinlock, flags);
454454
return NULL;
455455
}
456456

@@ -462,7 +462,7 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
462462
/* pairs with consumer's smp_load_acquire() */
463463
smp_store_release(&rb->producer_pos, new_prod_pos);
464464

465-
spin_unlock_irqrestore(&rb->spinlock, flags);
465+
raw_spin_unlock_irqrestore(&rb->spinlock, flags);
466466

467467
return (void *)hdr + BPF_RINGBUF_HDR_SZ;
468468
}

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