From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 12EAF6B004D for ; Tue, 9 Jun 2009 02:06:24 -0400 (EDT) References: <20090606080334.GA15204@ZenIV.linux.org.uk> <20090608162913.GL8633@ZenIV.linux.org.uk> <20090608175018.GM8633@ZenIV.linux.org.uk> From: ebiederm@xmission.com (Eric W. Biederman) Date: Mon, 08 Jun 2009 23:31:16 -0700 In-Reply-To: (Miklos Szeredi's message of "Tue\, 09 Jun 2009 07\:50\:38 +0200") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Subject: Re: [PATCH 0/23] File descriptor hot-unplug support v2 Sender: owner-linux-mm@kvack.org To: Miklos Szeredi Cc: viro@ZenIV.linux.org.uk, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, hugh@veritas.com, tj@kernel.org, adobriyan@gmail.com, torvalds@linux-foundation.org, alan@lxorguk.ukuu.org.uk, gregkh@suse.de, npiggin@suse.de, akpm@linux-foundation.org, hch@infradead.org List-ID: Miklos Szeredi writes: > On Mon, 8 Jun 2009, Al Viro wrote: >> On Mon, Jun 08, 2009 at 06:44:41PM +0200, Miklos Szeredi wrote: >> >> > I'm still not getting what the problem is. AFAICS file operations are >> > either >> > >> > a) non-interruptible but finish within a short time or >> > b) may block indefinitely but are interruptible (or at least killable). >> > >> > Anything else is already problematic, resulting in processes "stuck in >> > D state". >> >> Welcome to reality... >> >> * bread() is non-interruptible >> * so's copy_from_user()/copy_to_user() > > And why should revoke(2) care? Just wait for the damn thing to > finish. Why exactly do these need to be interruptible? Agreed. I expect the data size is going to be a page or less. Which is at most 64K on some weird architectures. I think that counts as a short time waiting for disk I/O. Baring thrashing. > Okay, if we want revoke or umount -f to be instantaneous then all that > needs to be taken care of. But does it *need* to be? Good question. I wonder what umount -f needs when we yank out a usb drive. > My idea of revoke is something like below: > > - make sure no new operations are started on the file > - check state of tasks for ongoing operations, if interruptible send signal Figuring out who to send a signal to is tricky. Still it should be doable in the common case. > - wait for all pending operations to finish > - kill file Eric -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org