From mboxrd@z Thu Jan 1 00:00:00 1970 From: Minchan Kim Subject: Re: [PATCH v2 0/3] File Sealing & memfd_create() Date: Mon, 2 Jun 2014 13:42:59 +0900 Message-ID: <20140602044259.GV10092@bbox> References: <1397587118-1214-1-git-send-email-dh.herrmann@gmail.com> <537396A2.9090609@cybernetics.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Hugh Dickins , Tony Battersby , Al Viro , Jan Kara , Michael Kerrisk , Ryan Lortie , Linus Torvalds , Andrew Morton , linux-mm , linux-fsdevel , linux-kernel , Johannes Weiner , Tejun Heo , Greg Kroah-Hartman , John Stultz , Kristian Hogsberg , Lennart Poettering , Daniel Mack , Kay Sievers , Peter Zijlstra To: David Herrmann Return-path: Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org Hello, On Mon, May 19, 2014 at 01:44:25PM +0200, David Herrmann wrote: > Hi > > On Thu, May 15, 2014 at 12:35 AM, Hugh Dickins wrote: > > The aspect which really worries me is this: the maintenance burden. > > This approach would add some peculiar new code, introducing a rare > > special case: which we might get right today, but will very easily > > forget tomorrow when making some other changes to mm. If we compile > > a list of danger areas in mm, this would surely belong on that list. > > I tried doing the page-replacement in the last 4 days, but honestly, > it's far more complex than I thought. So if no-one more experienced > with mm/ comes up with a simple implementation, I'll have to delay > this for some more weeks. > > However, I still wonder why we try to fix this as part of this > patchset. Using FUSE, a DIRECT-IO call can be delayed for an arbitrary > amount of time. Same is true for network block-devices, NFS, iscsi, > maybe loop-devices, ... This means, _any_ once mapped page can be > written to after an arbitrary delay. This can break any feature that > makes FS objects read-only (remounting read-only, setting S_IMMUTABLE, > sealing, ..). > > Shouldn't we try to fix the _cause_ of this? I didn't follow this patchset and couldn't find what's your most cocern but at a first glance, it seems you have troubled with pinned page. If so, it's really big problem for CMA and I think peterz's approach(ie, mm_mpin) is really make sense to me. https://lkml.org/lkml/2014/5/26/340 > > Isn't there a simple way to lock/mark/.. affected vmas in > get_user_pages(_fast)() and release them once done? We could increase > i_mmap_writable on all affected address_space and decrease it on > release. This would at least prevent sealing and could be check on > other operations, too (like setting S_IMMUTABLE). > This should be as easy as checking page_mapping(page) != NULL and then > adjusting ->i_mmap_writable in > get_writable_user_pages/put_writable_user_pages, right? > > Thanks > David > > -- > 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 -- Kind regards, Minchan Kim -- 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