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 <[email protected]>
---
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
Hi Sebastian,
kernel test robot noticed the following build warnings:
[auto build test WARNING on net-next/main]
url: https://github.com/intel-lab-lkp/linux/commits/Sebastian-Andrzej-Siewior/locking-local_lock-Introduce-guard-definition-for-local_lock/20231216-011911
base: net-next/main
patch link: https://lore.kernel.org/r/20231215171020.687342-5-bigeasy%40linutronix.de
patch subject: [PATCH net-next 04/24] net: Use nested-BH locking for napi_alloc_cache.
config: x86_64-randconfig-121-20231216 (https://download.01.org/0day-ci/archive/20231216/[email protected]/config)
compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231216/[email protected]/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
sparse warnings: (new ones prefixed by >>)
>> net/core/skbuff.c:302:38: sparse: sparse: incorrect type in argument 1 (different address spaces) @@ expected struct local_lock_t [usertype] *l @@ got struct local_lock_t [noderef] __percpu * @@
net/core/skbuff.c:302:38: sparse: expected struct local_lock_t [usertype] *l
net/core/skbuff.c:302:38: sparse: got struct local_lock_t [noderef] __percpu *
net/core/skbuff.c:331:38: sparse: sparse: incorrect type in argument 1 (different address spaces) @@ expected struct local_lock_t [usertype] *l @@ got struct local_lock_t [noderef] __percpu * @@
net/core/skbuff.c:331:38: sparse: expected struct local_lock_t [usertype] *l
net/core/skbuff.c:331:38: sparse: got struct local_lock_t [noderef] __percpu *
net/core/skbuff.c:734:17: sparse: sparse: incorrect type in argument 1 (different address spaces) @@ expected struct local_lock_t [usertype] *l @@ got struct local_lock_t [noderef] __percpu * @@
net/core/skbuff.c:734:17: sparse: expected struct local_lock_t [usertype] *l
net/core/skbuff.c:734:17: sparse: got struct local_lock_t [noderef] __percpu *
net/core/skbuff.c:806:9: sparse: sparse: incorrect type in argument 1 (different address spaces) @@ expected struct local_lock_t [usertype] *l @@ got struct local_lock_t [noderef] __percpu * @@
net/core/skbuff.c:806:9: sparse: expected struct local_lock_t [usertype] *l
net/core/skbuff.c:806:9: sparse: got struct local_lock_t [noderef] __percpu *
net/core/skbuff.c:1317:38: sparse: sparse: incorrect type in argument 1 (different address spaces) @@ expected struct local_lock_t [usertype] *l @@ got struct local_lock_t [noderef] __percpu * @@
net/core/skbuff.c:1317:38: sparse: expected struct local_lock_t [usertype] *l
net/core/skbuff.c:1317:38: sparse: got struct local_lock_t [noderef] __percpu *
net/core/skbuff.c: note: in included file (through include/linux/mmzone.h, include/linux/gfp.h, include/linux/umh.h, include/linux/kmod.h, ...):
include/linux/page-flags.h:242:46: sparse: sparse: self-comparison always evaluates to false
net/core/skbuff.c: note: in included file (through include/linux/mmzone.h, include/linux/gfp.h, include/linux/umh.h, include/linux/kmod.h, ...):
>> include/linux/local_lock.h:71:1: sparse: sparse: incorrect type in initializer (different address spaces) @@ expected void const [noderef] __percpu *__vpp_verify @@ got struct local_lock_t [usertype] * @@
include/linux/local_lock.h:71:1: sparse: expected void const [noderef] __percpu *__vpp_verify
include/linux/local_lock.h:71:1: sparse: got struct local_lock_t [usertype] *
>> include/linux/local_lock.h:71:1: sparse: sparse: incorrect type in initializer (different address spaces) @@ expected void const [noderef] __percpu *__vpp_verify @@ got struct local_lock_t [usertype] * @@
include/linux/local_lock.h:71:1: sparse: expected void const [noderef] __percpu *__vpp_verify
include/linux/local_lock.h:71:1: sparse: got struct local_lock_t [usertype] *
>> include/linux/local_lock.h:71:1: sparse: sparse: incorrect type in initializer (different address spaces) @@ expected void const [noderef] __percpu *__vpp_verify @@ got struct local_lock_t [usertype] * @@
include/linux/local_lock.h:71:1: sparse: expected void const [noderef] __percpu *__vpp_verify
include/linux/local_lock.h:71:1: sparse: got struct local_lock_t [usertype] *
net/core/skbuff.c: note: in included file (through include/net/net_namespace.h, include/linux/inet.h):
include/linux/skbuff.h:2715:28: sparse: sparse: self-comparison always evaluates to false
net/core/skbuff.c: note: in included file (through include/linux/skbuff.h, include/net/net_namespace.h, include/linux/inet.h):
include/net/checksum.h:33:39: sparse: sparse: incorrect type in argument 3 (different base types) @@ expected restricted __wsum [usertype] sum @@ got unsigned int @@
include/net/checksum.h:33:39: sparse: expected restricted __wsum [usertype] sum
include/net/checksum.h:33:39: sparse: got unsigned int
vim +302 net/core/skbuff.c
296
297 void *__napi_alloc_frag_align(unsigned int fragsz, unsigned int align_mask)
298 {
299 struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
300
301 fragsz = SKB_DATA_ALIGN(fragsz);
> 302 guard(local_lock_nested_bh)(&napi_alloc_cache.bh_lock);
303
304 return page_frag_alloc_align(&nc->page, fragsz, GFP_ATOMIC, align_mask);
305 }
306 EXPORT_SYMBOL(__napi_alloc_frag_align);
307
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
On 2023-12-16 12:43:23 [+0800], kernel test robot wrote:
> Hi Sebastian,
Hi,
> >> net/core/skbuff.c:302:38: sparse: sparse: incorrect type in argument 1 (different address spaces) @@ expected struct local_lock_t [usertype] *l @@ got struct local_lock_t [noderef] __percpu * @@
updated the guard definition for that.
Thanks for the report.
Sebastian