Commit bdacf3e3 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Jakub Kicinski
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net: Use nested-BH locking for napi_alloc_cache. 



napi_alloc_cache is a per-CPU variable and relies on disabled BH for its
locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT
this data structure requires explicit locking.

Add a local_lock_t to the data structure and use local_lock_nested_bh()
for locking. This change adds only lockdep coverage and does not alter
the functional behaviour for !PREEMPT_RT.

Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20240620132727.660738-5-bigeasy@linutronix.de


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 43d7ca29

net/core/skbuff.c

+24 −5
Original line number Diff line number Diff line
@@ -277,6 +277,7 @@ static void *page_frag_alloc_1k(struct page_frag_1k *nc, gfp_t gfp_mask) 
#endif



struct napi_alloc_cache {

	local_lock_t bh_lock;

	struct page_frag_cache page;

	struct page_frag_1k page_small;

	unsigned int skb_count;
@@ -284,7 +285,9 @@ struct napi_alloc_cache { 
};



static DEFINE_PER_CPU(struct page_frag_cache, netdev_alloc_cache);

static DEFINE_PER_CPU(struct napi_alloc_cache, napi_alloc_cache);

static DEFINE_PER_CPU(struct napi_alloc_cache, napi_alloc_cache) = {

	.bh_lock = INIT_LOCAL_LOCK(bh_lock),

};



/* Double check that napi_get_frags() allocates skbs with

 * skb->head being backed by slab, not a page fragment.
@@ -306,11 +309,16 @@ void napi_get_frags_check(struct napi_struct *napi) 
void *__napi_alloc_frag_align(unsigned int fragsz, unsigned int align_mask)

{

	struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);

	void *data;



	fragsz = SKB_DATA_ALIGN(fragsz);



	return __page_frag_alloc_align(&nc->page, fragsz, GFP_ATOMIC,

	local_lock_nested_bh(&napi_alloc_cache.bh_lock);

	data = __page_frag_alloc_align(&nc->page, fragsz, GFP_ATOMIC,

				       align_mask);

	local_unlock_nested_bh(&napi_alloc_cache.bh_lock);

	return data;



}

EXPORT_SYMBOL(__napi_alloc_frag_align);
@@ -338,16 +346,20 @@ static struct sk_buff *napi_skb_cache_get(void) 
	struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);

	struct sk_buff *skb;



	local_lock_nested_bh(&napi_alloc_cache.bh_lock);

	if (unlikely(!nc->skb_count)) {

		nc->skb_count = kmem_cache_alloc_bulk(net_hotdata.skbuff_cache,

						      GFP_ATOMIC,

						      NAPI_SKB_CACHE_BULK,

						      nc->skb_cache);

		if (unlikely(!nc->skb_count))

		if (unlikely(!nc->skb_count)) {

			local_unlock_nested_bh(&napi_alloc_cache.bh_lock);

			return NULL;

		}

	}



	skb = nc->skb_cache[--nc->skb_count];

	local_unlock_nested_bh(&napi_alloc_cache.bh_lock);

	kasan_mempool_unpoison_object(skb, kmem_cache_size(net_hotdata.skbuff_cache));



	return skb;
@@ -740,9 +752,13 @@ struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int len, 
		pfmemalloc = nc->pfmemalloc;

	} else {

		local_bh_disable();

		local_lock_nested_bh(&napi_alloc_cache.bh_lock);



		nc = this_cpu_ptr(&napi_alloc_cache.page);

		data = page_frag_alloc(nc, len, gfp_mask);

		pfmemalloc = nc->pfmemalloc;



		local_unlock_nested_bh(&napi_alloc_cache.bh_lock);

		local_bh_enable();

	}
@@ -806,11 +822,11 @@ struct sk_buff *napi_alloc_skb(struct napi_struct *napi, unsigned int len) 
		goto skb_success;

	}



	nc = this_cpu_ptr(&napi_alloc_cache);



	if (sk_memalloc_socks())

		gfp_mask |= __GFP_MEMALLOC;



	local_lock_nested_bh(&napi_alloc_cache.bh_lock);

	nc = this_cpu_ptr(&napi_alloc_cache);

	if (NAPI_HAS_SMALL_PAGE_FRAG && len <= SKB_WITH_OVERHEAD(1024)) {

		/* we are artificially inflating the allocation size, but

		 * that is not as bad as it may look like, as:
@@ -832,6 +848,7 @@ struct sk_buff *napi_alloc_skb(struct napi_struct *napi, unsigned int len) 
		data = page_frag_alloc(&nc->page, len, gfp_mask);

		pfmemalloc = nc->page.pfmemalloc;

	}

	local_unlock_nested_bh(&napi_alloc_cache.bh_lock);



	if (unlikely(!data))

		return NULL;
@@ -1431,6 +1448,7 @@ static void napi_skb_cache_put(struct sk_buff *skb) 
	if (!kasan_mempool_poison_object(skb))

		return;



	local_lock_nested_bh(&napi_alloc_cache.bh_lock);

	nc->skb_cache[nc->skb_count++] = skb;



	if (unlikely(nc->skb_count == NAPI_SKB_CACHE_SIZE)) {
@@ -1442,6 +1460,7 @@ static void napi_skb_cache_put(struct sk_buff *skb) 
				     nc->skb_cache + NAPI_SKB_CACHE_HALF);

		nc->skb_count = NAPI_SKB_CACHE_HALF;

	}

	local_unlock_nested_bh(&napi_alloc_cache.bh_lock);

}



void __napi_kfree_skb(struct sk_buff *skb, enum skb_drop_reason reason)