From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <380771D1.25616711@colorfullife.com> Date: Fri, 15 Oct 1999 20:26:25 +0200 From: Manfred Spraul MIME-Version: 1.0 Subject: Re: [PATCH] kanoj-mm17-2.3.21 kswapd vma scanning protection References: <199910151638.JAA72758@google.engr.sgi.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Kanoj Sarcar Cc: torvalds@transmeta.com, sct@redhat.com, andrea@suse.de, viro@math.psu.edu, linux-mm@kvack.org, linux-kernel@vger.rutgers.edu List-ID: Kanoj Sarcar wrote: > If you wanted to be more careful, you > could define the swapout prototype as swapout(start, end, flags, file). > That *should* be enough for most future 2.3/2.4 driver. "file" can go away if you do not call "get_file()" before releasing the locking. > > > - swap_out() is called with the semaphore held, > > Look below for why this is not safe. You are right, this can lock-up. Swapper is only protected from reentrancy on it's own stack, not from reentrancy from another thread. > > > Or: ->swapout() releases the semaphore, > > > > This works for filemap_swapout, but you can not expect every regular Joe > driver writer to adhere to this rule. The result is not a rare lock-up, but it will lock-up nearly immediately. Even Joe would notice that. [I know this is ugly] > And here's one more. Before invoking swapout(), and before loosing the > vmlist_lock in try_to_swap_out, the vma might be marked with a flag > that indicates that swapout() is looking at the vma. Or: use a multiple reader - single writer semaphore with "starve writer" policy. IMO that's cleaner than a semaphore with an attached waitqueue for do_munmap(). > This swapout() cleanup is independent of the patch I have already posted, > so the patch should be integrated into 2.3, while we debate how to tackle > the cleanup. Ok. -- Manfred -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://humbolt.geo.uu.nl/Linux-MM/