From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH] md / procfs: avoid Oops if md-mod removed while /proc/mdstat is being polled. Date: Thu, 27 Feb 2014 12:58:07 -0800 Message-ID: <20140227125807.d034c50c7fe2e1a9f3c38ec1@linux-foundation.org> References: <20140227172445.13644477@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Alexander Viro , linux-fsdevel@vger.kernel.org, linux RAID , "majianpeng" , lkml To: NeilBrown Return-path: In-Reply-To: <20140227172445.13644477@notabene.brown> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, 27 Feb 2014 17:24:45 +1100 NeilBrown wrote: > If poll or select is waiting on /proc/mdstat when md-mod is unloaded > an oops will ensure when the poll/select completes. > > This is because the wait_queue_head which is registered with poll_wait() > is local to the module and no longer exists when the poll completes and > detaches that wait_queue_head (in poll_free_wait -> remove_wait_queue). > > To fix this we need the wait_queue_head to have (at least) the same life > time as the proc_dir_entry. So this patch places it in that structure. > > We: > - add pde_poll_wait to struct proc_dir_entry > - call poll_wait() passing this when poll() is called on the proc file > - export a function proc_wake_up which will call wake_up() on pde_poll_wait > > and make use of all that in md.c This sounds wrong. If a userspace process is waiting on md_event_waiters then the md module is "busy" and the rmmod attempt should fail?