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: 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it")
Reported-by: Brian Grech <bgrech@redhat.com>
Signed-off-by: Wander Lairson Costa <wander.lairson@gmail.com>
Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20240920190700.617253-1-wander@redhat.com

diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index e20b90c..de3b681 100644 (file)
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -29,7 +29,7 @@ struct bpf_ringbuf {
        u64 mask;
        struct page **pages;
        int nr_pages;
-       spinlock_t spinlock ____cacheline_aligned_in_smp;
+       raw_spinlock_t spinlock ____cacheline_aligned_in_smp;
        /* For user-space producer ring buffers, an atomic_t busy bit is used
         * to synchronize access to the ring buffers in the kernel, rather than
         * 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)
        if (!rb)
                return NULL;
 
-       spin_lock_init(&rb->spinlock);
+       raw_spin_lock_init(&rb->spinlock);
        atomic_set(&rb->busy, 0);
        init_waitqueue_head(&rb->waitq);
        init_irq_work(&rb->work, bpf_ringbuf_notify);
@@ -421,10 +421,10 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
        cons_pos = smp_load_acquire(&rb->consumer_pos);
 
        if (in_nmi()) {
-               if (!spin_trylock_irqsave(&rb->spinlock, flags))
+               if (!raw_spin_trylock_irqsave(&rb->spinlock, flags))
                        return NULL;
        } else {
-               spin_lock_irqsave(&rb->spinlock, flags);
+               raw_spin_lock_irqsave(&rb->spinlock, flags);
        }
 
        pend_pos = rb->pending_pos;
@@ -450,7 +450,7 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
         */
        if (new_prod_pos - cons_pos > rb->mask ||
            new_prod_pos - pend_pos > rb->mask) {
-               spin_unlock_irqrestore(&rb->spinlock, flags);
+               raw_spin_unlock_irqrestore(&rb->spinlock, flags);
                return NULL;
        }
 
@@ -462,7 +462,7 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
        /* pairs with consumer's smp_load_acquire() */
        smp_store_release(&rb->producer_pos, new_prod_pos);
 
-       spin_unlock_irqrestore(&rb->spinlock, flags);
+       raw_spin_unlock_irqrestore(&rb->spinlock, flags);
 
        return (void *)hdr + BPF_RINGBUF_HDR_SZ;
 }