• Zhen Wei's avatar
    ocfs2: introduce sc->sc_send_lock to protect outbound outbound messages · 925037bc
    Zhen Wei authored
    When there is a lot of multithreaded I/O usage, two threads can collide
    while sending out a message to the other nodes. This is due to the lack of
    locking between threads while sending out the messages.
    
    When a connected TCP send(), sendto(), or sendmsg() arrives in the Linux
    kernel, it eventually comes through tcp_sendmsg(). tcp_sendmsg() protects
    itself by acquiring a lock at invocation by calling lock_sock().
    tcp_sendmsg() then loops over the buffers in the iovec, allocating
    associated sk_buff's and cache pages for use in the actual send. As it does
    so, it pushes the data out to tcp for actual transmission. However, if one
    of those allocation fails (because a large number of large sends is being
    processed, for example), it must wait for memory to become available. It
    does so by jumping to wait_for_sndbuf or wait_for_memory, both of which
    eventually cause a call to sk_stream_wait_memory(). sk_stream_wait_memory()
    contains a code path that calls sk_wait_event(). Finally, sk_wait_event()
    contains the call to release_sock().
    
    The following patch adds a lock to the socket container in order to
    properly serialize outbound requests.
    
    From: Zhen Wei <zwei@novell.com>
    Acked-by: default avatarJeff Mahoney <jeffm@suse.com>
    Signed-off-by: default avatarMark Fasheh <mark.fasheh@oracle.com>
    925037bc
tcp.c 54.6 KB