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net: Use nested-BH locking for napi_alloc_cache.

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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: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20240620132727.660738-5-bigeasy@linutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Sebastian Andrzej Siewior 2024-06-20 15:21:54 +02:00 committed by Jakub Kicinski
parent 43d7ca2907
commit bdacf3e349
1 changed files with 24 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
net/core/skbuff.c
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@ -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)