From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta12.messagelabs.com (mail6.bemta12.messagelabs.com [216.82.250.247]) by kanga.kvack.org (Postfix) with ESMTP id 440C16B004A for ; Mon, 6 Jun 2011 18:16:53 -0400 (EDT) Date: Mon, 6 Jun 2011 15:16:14 -0700 From: Andrew Morton Subject: Re: [PATCH] mm: Fix assertion mapping->nrpages == 0 in end_writeback() Message-Id: <20110606151614.0037e236.akpm@linux-foundation.org> In-Reply-To: <1306748258-4732-1-git-send-email-jack@suse.cz> References: <1306748258-4732-1-git-send-email-jack@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Jan Kara Cc: linux-mm@kvack.org, Al Viro , mszeredi@suse.cz, Jay , stable@kernel.org, Nick Piggin On Mon, 30 May 2011 11:37:38 +0200 Jan Kara wrote: > Under heavy memory and filesystem load, users observe the assertion > mapping->nrpages == 0 in end_writeback() trigger. This can be caused > by page reclaim reclaiming the last page from a mapping in the following > race: > CPU0 CPU1 > ... > shrink_page_list() > __remove_mapping() > __delete_from_page_cache() > radix_tree_delete() > evict_inode() > truncate_inode_pages() > truncate_inode_pages_range() > pagevec_lookup() - finds nothing > end_writeback() > mapping->nrpages != 0 -> BUG > page->mapping = NULL > mapping->nrpages-- > > Fix the problem by cycling the mapping->tree_lock at the end of > truncate_inode_pages_range() to synchronize with page reclaim. > > Analyzed by Jay , lost in LKML, and dug > out by Miklos Szeredi . > > CC: Jay > CC: stable@kernel.org > Acked-by: Miklos Szeredi > Signed-off-by: Jan Kara > --- > mm/truncate.c | 7 +++++++ > 1 files changed, 7 insertions(+), 0 deletions(-) > > Andrew, would you merge this patch please? Thanks. > > diff --git a/mm/truncate.c b/mm/truncate.c > index a956675..ec3d292 100644 > --- a/mm/truncate.c > +++ b/mm/truncate.c > @@ -291,6 +291,13 @@ void truncate_inode_pages_range(struct address_space *mapping, > pagevec_release(&pvec); > mem_cgroup_uncharge_end(); > } > + /* > + * Cycle the tree_lock to make sure all __delete_from_page_cache() > + * calls run from page reclaim have finished as well (this handles the > + * case when page reclaim took the last page from our range). > + */ > + spin_lock_irq(&mapping->tree_lock); > + spin_unlock_irq(&mapping->tree_lock); > } > EXPORT_SYMBOL(truncate_inode_pages_range); That's one ugly patch. Perhaps this regression was added by Nick's RCUification of pagecache. Before that patch, mapping->nrpages and the radix-tree state were coherent for holders of tree_lock. So pagevec_lookup() would never return "no pages" while ->nrpages is non-zero. After that patch, find_get_pages() uses RCU to protect the radix-tree but I don't think it correctly protects the aggregate (radix-tree + nrpages). If it's not that then I see another possibility. truncate_inode_pages_range() does if (mapping->nrpages == 0) return; Is there anything to prevent a page getting added to the inode _after_ this test? i_mutex? If not, that would trigger the BUG. Either way, I don't think that the uglypatch expresses a full understanding of te bug ;) -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org