On Sun, 4 Feb 2007 12:03:17 +0100 Nick Piggin <npiggin@xxxxxxx> wrote: > On Sun, Feb 04, 2007 at 02:56:02AM -0800, Andrew Morton wrote: > > On Sun, 4 Feb 2007 11:46:09 +0100 Nick Piggin <npiggin@xxxxxxx> wrote: > > > > > On Sun, Feb 04, 2007 at 02:30:55AM -0800, Andrew Morton wrote: > > > > On Sun, 4 Feb 2007 11:15:29 +0100 Nick Piggin <npiggin@xxxxxxx> wrote: > > > > > > > > > The write path is broken. I prefer my kernels slow, than buggy. > > > > > > > > That won't fly. > > > > > > What won't fly? > > > > I suspect the performance cost of this approach would force us to redo it > > all. > > That's the idea. But at least in the meantime we're correct. There's no way I'd support merging a change which we know we'll have to redo only we have no clue how. > > If that recollection is right, I think we could afford to reintroduce that > > problem, frankly. Especially as it only happens in the incredibly rare > > case of that get_user()ed page getting unmapped under our feet. > > Dang. I was hoping to fix it without introducing data corruption. Well. It's a compromise. Being practical about it, I reeeealy doubt that anyone will hit this combination of circumstances. > > > > > but you introduce the theoretical memory deadlock > > > > > where a task cannot reclaim its own memory. > > > > > > > > Nah, that'll never happen - both pages are already allocated. > > > > > > Both pages? I don't get it. > > > > > > You set the don't-reclaim vma flag, then run get_user, which takes a > > > page fault and potentially has to allocate N pages for pagetables, > > > pagecache readahead, buffers and fs private data and pagecache radix > > > tree nodes for all of the pages read in. > > > > Oh, OK. Need to do the get_user() twice then. Once before taking that new > > rwsem. > > Race condition remains. No, not in a million years. - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
