Patch "tcp: annotate data-race around tcp_md5sig_pool_populated" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    tcp: annotate data-race around tcp_md5sig_pool_populated

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tcp-annotate-data-race-around-tcp_md5sig_pool_popula.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5a22eb2129e55a9e43d45904cfcb4b7b7c109369
Author: Eric Dumazet <edumazet@xxxxxxxxxx>
Date:   Mon Aug 22 21:15:28 2022 +0000

    tcp: annotate data-race around tcp_md5sig_pool_populated
    
    [ 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@xxxxxxxxxxxx>
    Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index b604c7664350..5b4e170b6a34 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4331,12 +4331,16 @@ 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) {
@@ -4347,7 +4351,8 @@ 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);
 
@@ -4363,7 +4368,8 @@ 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);