[PATCH AUTOSEL 6.0 13/77] tcp: annotate data-race around tcp_md5sig_pool_populated

Sasha Levin
2022-10-09T22:09:47Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit aacd467c0a576e5e44d2de4205855dc0fe43f6fb ]

tcp_md5sig_pool_populated can be read while another thread
changes its value.

The race has no consequence because allocations
are protected with tcp_md5sig_mutex.

This patch adds READ_ONCE() and WRITE_ONCE() to document
the race and silence KCSAN.

Reported-by: Abhishek Shah <abhishek.shah@columbia.edu>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/tcp.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e373dde1f46f..3733742cebf8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4442,12 +4442,16 @@ static void __tcp_alloc_md5sig_pool(void)
* to memory. See smp_rmb() in tcp_get_md5sig_pool()
*/
smp_wmb();
- tcp_md5sig_pool_populated = true;
+ /* Paired with READ_ONCE() from tcp_alloc_md5sig_pool()
+ * and tcp_get_md5sig_pool().
+ */
+ WRITE_ONCE(tcp_md5sig_pool_populated, true);
}

bool tcp_alloc_md5sig_pool(void)
{
- if (unlikely(!tcp_md5sig_pool_populated)) {
+ /* Paired with WRITE_ONCE() from __tcp_alloc_md5sig_pool() */
+ if (unlikely(!READ_ONCE(tcp_md5sig_pool_populated))) {
mutex_lock(&tcp_md5sig_mutex);

if (!tcp_md5sig_pool_populated) {
@@ -4458,7 +4462,8 @@ bool tcp_alloc_md5sig_pool(void)

mutex_unlock(&tcp_md5sig_mutex);
}
- return tcp_md5sig_pool_populated;
+ /* Paired with WRITE_ONCE() from __tcp_alloc_md5sig_pool() */
+ return READ_ONCE(tcp_md5sig_pool_populated);
}
EXPORT_SYMBOL(tcp_alloc_md5sig_pool);

@@ -4474,7 +4479,8 @@ struct tcp_md5sig_pool *tcp_get_md5sig_pool(void)
{
local_bh_disable();

- if (tcp_md5sig_pool_populated) {
+ /* Paired with WRITE_ONCE() from __tcp_alloc_md5sig_pool() */
+ if (READ_ONCE(tcp_md5sig_pool_populated)) {
/* coupled with smp_wmb() in __tcp_alloc_md5sig_pool() */
smp_rmb();
return this_cpu_ptr(&tcp_md5sig_pool);
--
2.35.1