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    Subject[PATCH 5.4 195/255] tcp: annotate data-race around tcp_md5sig_pool_populated
    Date
    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 2da4f852fc58..aeeeaf2d6482 100644
    --- a/net/ipv4/tcp.c
    +++ b/net/ipv4/tcp.c
    @@ -3770,12 +3770,16 @@ 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) {
    @@ -3786,7 +3790,8 @@ 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);

    @@ -3802,7 +3807,8 @@ 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


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