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Date: Fri, 15 Dec 2023 18:07:23 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: linux-kernel@...r.kernel.org,
netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
Boqun Feng <boqun.feng@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
Eric Dumazet <edumazet@...gle.com>,
Frederic Weisbecker <frederic@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Waiman Long <longman@...hat.com>,
Will Deacon <will@...nel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH net-next 04/24] 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: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
net/core/skbuff.c | 57 +++++++++++++++++++++++++++--------------------
1 file changed, 33 insertions(+), 24 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index de9397e45718a..9c3073dcc80f1 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -265,6 +265,7 @@ 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;
@@ -272,7 +273,9 @@ 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.
@@ -296,6 +299,7 @@ void *__napi_alloc_frag_align(unsigned int fragsz, unsigned int align_mask)
struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
fragsz = SKB_DATA_ALIGN(fragsz);
+ guard(local_lock_nested_bh)(&napi_alloc_cache.bh_lock);
return page_frag_alloc_align(&nc->page, fragsz, GFP_ATOMIC, align_mask);
}
@@ -324,6 +328,7 @@ static struct sk_buff *napi_skb_cache_get(void)
struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
struct sk_buff *skb;
+ guard(local_lock_nested_bh)(&napi_alloc_cache.bh_lock);
if (unlikely(!nc->skb_count)) {
nc->skb_count = kmem_cache_alloc_bulk(skbuff_cache,
GFP_ATOMIC,
@@ -726,9 +731,11 @@ struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int len,
pfmemalloc = nc->pfmemalloc;
} else {
local_bh_disable();
- nc = this_cpu_ptr(&napi_alloc_cache.page);
- data = page_frag_alloc(nc, len, gfp_mask);
- pfmemalloc = nc->pfmemalloc;
+ scoped_guard(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_bh_enable();
}
@@ -793,31 +800,32 @@ 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;
- 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:
- * - 'len' less than GRO_MAX_HEAD makes little sense
- * - On most systems, larger 'len' values lead to fragment
- * size above 512 bytes
- * - kmalloc would use the kmalloc-1k slab for such values
- * - Builds with smaller GRO_MAX_HEAD will very likely do
- * little networking, as that implies no WiFi and no
- * tunnels support, and 32 bits arches.
- */
- len = SZ_1K;
+ scoped_guard(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:
+ * - 'len' less than GRO_MAX_HEAD makes little sense
+ * - On most systems, larger 'len' values lead to fragment
+ * size above 512 bytes
+ * - kmalloc would use the kmalloc-1k slab for such values
+ * - Builds with smaller GRO_MAX_HEAD will very likely do
+ * little networking, as that implies no WiFi and no
+ * tunnels support, and 32 bits arches.
+ */
+ len = SZ_1K;
- data = page_frag_alloc_1k(&nc->page_small, gfp_mask);
- pfmemalloc = NAPI_SMALL_PAGE_PFMEMALLOC(nc->page_small);
- } else {
- len = SKB_HEAD_ALIGN(len);
+ data = page_frag_alloc_1k(&nc->page_small, gfp_mask);
+ pfmemalloc = NAPI_SMALL_PAGE_PFMEMALLOC(nc->page_small);
+ } else {
+ len = SKB_HEAD_ALIGN(len);
- data = page_frag_alloc(&nc->page, len, gfp_mask);
- pfmemalloc = nc->page.pfmemalloc;
+ data = page_frag_alloc(&nc->page, len, gfp_mask);
+ pfmemalloc = nc->page.pfmemalloc;
+ }
}
if (unlikely(!data))
@@ -1306,6 +1314,7 @@ static void napi_skb_cache_put(struct sk_buff *skb)
struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
u32 i;
+ guard(local_lock_nested_bh)(&napi_alloc_cache.bh_lock);
kasan_poison_object_data(skbuff_cache, skb);
nc->skb_cache[nc->skb_count++] = skb;
--
2.43.0
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