From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 7F1CE6B0200 for ; Fri, 27 Aug 2010 05:55:53 -0400 (EDT) Date: Fri, 27 Aug 2010 11:55:46 +0200 From: Andrea Arcangeli Subject: Re: [PATCH] mm: fix hang on anon_vma->root->lock Message-ID: <20100827095546.GC6803@random.random> References: <20100826235052.GZ6803@random.random> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: Hugh Dickins Cc: Linus Torvalds , Andrew Morton , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Thu, Aug 26, 2010 at 06:43:31PM -0700, Hugh Dickins wrote: > some light., I think you're mistaking the role that RCU plays here. That's exactly correct, I thought it prevented reuse of the slab entry, not only of the whole slab... SLAB_DESTROY_BY_RCU is a lot more tricky to use than I though... However at the light of this, I think page_lock_anon_vma could have returned a freed and reused anon_vma well before the anon-vma changes. The anon_vma could have been freed after the first page_mapped check succeed but before taking the spinlock. I think, it worked fine because the rmap walks are robust enough just not to fall apart on a reused anon_vma while the lock is hold. It become a visible problem now because we were unlocking the wrong lock leading to a deadlock. But I guess it wasn't too intentional to return a reused anon_vma out of page_lock_anon_vma. -- 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