[PATCH 3.16 181/294] epoll: fix race between ep_poll_callback(POLLFREE) and ep_free()/ep_remove()

3.16.50-rc1 review patch. If anyone has any objections, please let me know. -- From: Oleg Nesterov commit 138e4ad67afd5c6c318b056b4d17c17f2c0ca5c0 upstream. The race was introduced by me in commit 971316f0503a ("epoll: ep_unregister_pollwait() can use the

[PATCH 3.16 181/294] epoll: fix race between ep_poll_callback(POLLFREE) and ep_free()/ep_remove()

3.16.50-rc1 review patch. If anyone has any objections, please let me know. -- From: Oleg Nesterov commit 138e4ad67afd5c6c318b056b4d17c17f2c0ca5c0 upstream. The race was introduced by me in commit 971316f0503a ("epoll: ep_unregister_pollwait() can use the freed pwq->whead").