socket: fix issue on concurrent handle of a socket

Found an issue on concurrent invoke of event handler to the same socket
fd, causing memory corruption. This issue arises after applying commit
"socket: Remove redundant in_lock in incoming message handling" that
removes priv->in_lock to serialize socket read.

The following call sequence describes how concurrent socket event handle
happens.
   thread 1                    thread 2                thread 3
epoll_wait() return
(slot->in_handler is 0)  call select_on_epoll()
                         and epoll_ctl() on fd
                                                    epoll_wait() return
slot->in_handler++
(slot->in_handler is 1)
                                                    slot->in_handler++
                                                    (slot->in_handler is 2)
call handler()                                      call handler()

Fix this issue by skip invoke of handler if there is already a handler
inprogress.

Change-Id: I437126ac772debcadb00993a948919c931cd607b
updates: bz#1467614
Signed-off-by: Zhang Huan <zhanghuan@open-fs.com>

0 files changed, 0 insertions, 0 deletions