From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jonathan Corbet Subject: Re: [RFC][PATCH 5/9] vfs: Introduce basic infrastructure for revoking a file Date: Tue, 14 Apr 2009 16:12:40 -0600 Message-ID: <20090414161240.73fe6bcd@bike.lwn.net> References: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit Cc: Andrew Morton , , , , , Al Viro , Hugh Dickins , Tejun Heo , Alexey Dobriyan , Linus Torvalds , Alan Cox , Greg Kroah-Hartman To: ebiederm@xmission.com (Eric W. Biederman) Return-path: In-Reply-To: Sender: linux-pci-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Hi, Eric, One little thing I noticed as I was looking at this... > +int fops_substitute(struct file *file, const struct file_operations *f_op, > + struct vm_operations_struct *vm_ops) > +{ [...] > + /* > + * Wait until there are no more callers in the original > + * file_operations methods. > + */ > + while (atomic_long_read(&file->f_use) > 0) > + schedule_timeout_interruptible(1); You use an interruptible sleep here, but there's no signal check to get you out of the loop. So it's not really interruptible. If f_use never goes to zero (a distressingly likely possibility, I fear), this code will create the equivalent of an unkillable D-wait state without ever actually showing up that way in "ps". Actually, now that I look, once you've got a signal pending you'll stay in TASK_RUNNING, so the above could turn into a busy-wait. Unless I've missed something...? I have no idea what the right thing to do in the face of a signal would be. Perhaps the wait-for-zero and release() call stuff should be dumped into a workqueue and done asynchronously? OTOH, I can see a need to know when the revoke operation is really done... jon