tree 5a928f3d3f8488d1094a4ced8f39228c9d5a8ca9
parent f71aa8a55a0ae1a0d06c6079265d16502a678e8e
author Zhen Wei <zwei@novell.com> 1169601599 -0800
committer Mark Fasheh <mark.fasheh@oracle.com> 1170879311 -0800

ocfs2: introduce sc->sc_send_lock to protect outbound outbound messages

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: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>