[PATCH bpf v1] bpf: Drop rqspinlock usage in ringbuf

[Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>]

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.

Reported-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: a650d38915c1 ("bpf: Convert ringbuf map to rqspinlock")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
---
 kernel/bpf/ringbuf.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index 719d73299397..1499d8caa9a3 100644
--- a/kernel/bpf/ringbuf.c
+++ b/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;
 }
--
2.50.0