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Subject[PATCH 3.2 23/27] tcp: md5: do not use alloc_percpu()
3.2.66-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>

commit 349ce993ac706869d553a1816426d3a4bfda02b1 upstream.

percpu tcp_md5sig_pool contains memory blobs that ultimately
go through sg_set_buf().

-> sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));

This requires that whole area is in a physically contiguous portion
of memory. And that @buf is not backed by vmalloc().

Given that alloc_percpu() can use vmalloc() areas, this does not
fit the requirements.

Replace alloc_percpu() by a static DEFINE_PER_CPU() as tcp_md5sig_pool
is small anyway, there is no gain to dynamically allocate it.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: 765cf9976e93 ("tcp: md5: remove one indirection level in tcp_md5sig_pool")
Reported-by: Crestez Dan Leonard <cdleonard@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: the deleted code differs slightly due to API changes]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv4/tcp.c | 59 ++++++++++++++++++++--------------------------------------
1 file changed, 20 insertions(+), 39 deletions(-)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2863,61 +2863,42 @@ int tcp_gro_complete(struct sk_buff *skb
EXPORT_SYMBOL(tcp_gro_complete);

#ifdef CONFIG_TCP_MD5SIG
-static struct tcp_md5sig_pool __percpu *tcp_md5sig_pool __read_mostly;
+static DEFINE_PER_CPU(struct tcp_md5sig_pool, tcp_md5sig_pool);
static DEFINE_MUTEX(tcp_md5sig_mutex);
-
-static void __tcp_free_md5sig_pool(struct tcp_md5sig_pool __percpu *pool)
-{
- int cpu;
-
- for_each_possible_cpu(cpu) {
- struct tcp_md5sig_pool *p = per_cpu_ptr(pool, cpu);
-
- if (p->md5_desc.tfm)
- crypto_free_hash(p->md5_desc.tfm);
- }
- free_percpu(pool);
-}
+static bool tcp_md5sig_pool_populated = false;

static void __tcp_alloc_md5sig_pool(void)
{
int cpu;
- struct tcp_md5sig_pool __percpu *pool;
-
- pool = alloc_percpu(struct tcp_md5sig_pool);
- if (!pool)
- return;

for_each_possible_cpu(cpu) {
- struct crypto_hash *hash;
+ if (!per_cpu(tcp_md5sig_pool, cpu).md5_desc.tfm) {
+ struct crypto_hash *hash;

- hash = crypto_alloc_hash("md5", 0, CRYPTO_ALG_ASYNC);
- if (!hash || IS_ERR(hash))
- goto out_free;
-
- per_cpu_ptr(pool, cpu)->md5_desc.tfm = hash;
+ hash = crypto_alloc_hash("md5", 0, CRYPTO_ALG_ASYNC);
+ if (IS_ERR_OR_NULL(hash))
+ return;
+ per_cpu(tcp_md5sig_pool, cpu).md5_desc.tfm = hash;
+ }
}
- /* before setting tcp_md5sig_pool, we must commit all writes
- * to memory. See ACCESS_ONCE() in tcp_get_md5sig_pool()
+ /* before setting tcp_md5sig_pool_populated, we must commit all writes
+ * to memory. See smp_rmb() in tcp_get_md5sig_pool()
*/
smp_wmb();
- tcp_md5sig_pool = pool;
- return;
-out_free:
- __tcp_free_md5sig_pool(pool);
+ tcp_md5sig_pool_populated = true;
}

bool tcp_alloc_md5sig_pool(void)
{
- if (unlikely(!tcp_md5sig_pool)) {
+ if (unlikely(!tcp_md5sig_pool_populated)) {
mutex_lock(&tcp_md5sig_mutex);

- if (!tcp_md5sig_pool)
+ if (!tcp_md5sig_pool_populated)
__tcp_alloc_md5sig_pool();

mutex_unlock(&tcp_md5sig_mutex);
}
- return tcp_md5sig_pool != NULL;
+ return tcp_md5sig_pool_populated;
}
EXPORT_SYMBOL(tcp_alloc_md5sig_pool);

@@ -2931,13 +2912,13 @@ EXPORT_SYMBOL(tcp_alloc_md5sig_pool);
*/
struct tcp_md5sig_pool *tcp_get_md5sig_pool(void)
{
- struct tcp_md5sig_pool __percpu *p;
-
local_bh_disable();
- p = ACCESS_ONCE(tcp_md5sig_pool);
- if (p)
- return __this_cpu_ptr(p);

+ if (tcp_md5sig_pool_populated) {
+ /* coupled with smp_wmb() in __tcp_alloc_md5sig_pool() */
+ smp_rmb();
+ return this_cpu_ptr(&tcp_md5sig_pool);
+ }
local_bh_enable();
return NULL;
}


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