bpf: Drop rqspinlock usage in ringbuf

We noticed potential lock ups and delays in progs running in NMI context
with the rqspinlock changes, which suggests more improvements need to be
made before we can support ring buffer updates in such a context safely.
Revert the change for now.

Fixes: a650d38 ("bpf: Convert ringbuf map to rqspinlock")
Reported-by: Josef Bacik <[email protected]>
Signed-off-by: Kumar Kartikeya Dwivedi <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/bpf/[email protected]

Author: kkdwivedi

kernel/bpf/ringbuf.c

@@ -11,7 +11,6 @@
 #include <linux/kmemleak.h>
 #include <uapi/linux/btf.h>
 #include <linux/btf_ids.h>
-#include <asm/rqspinlock.h>
 
 #define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE)
 
@@ -30,7 +29,7 @@ struct bpf_ringbuf {
 	u64 mask;
 	struct page **pages;
 	int nr_pages;
-	rqspinlock_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
@@ -174,7 +173,7 @@ static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
 	if (!rb)
 		return NULL;
 
-	raw_res_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);
@@ -417,8 +416,12 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
 
 	cons_pos = smp_load_acquire(&rb->consumer_pos);
 
-	if (raw_res_spin_lock_irqsave(&rb->spinlock, flags))
-		return NULL;
+	if (in_nmi()) {
+		if (!raw_spin_trylock_irqsave(&rb->spinlock, flags))
+			return NULL;
+	} else {
+		raw_spin_lock_irqsave(&rb->spinlock, flags);
+	}
 
 	pend_pos = rb->pending_pos;
 	prod_pos = rb->producer_pos;
@@ -443,7 +446,7 @@ 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) {
-		raw_res_spin_unlock_irqrestore(&rb->spinlock, flags);
+		raw_spin_unlock_irqrestore(&rb->spinlock, flags);
 		return NULL;
 	}
 
@@ -455,7 +458,7 @@ 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);
 
-	raw_res_spin_unlock_irqrestore(&rb->spinlock, flags);
+	raw_spin_unlock_irqrestore(&rb->spinlock, flags);
 
 	return (void *)hdr + BPF_RINGBUF_HDR_SZ;
 }