From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 1728B6B0130 for ; Mon, 20 Jun 2011 20:19:07 -0400 (EDT) Date: Mon, 20 Jun 2011 17:18:33 -0700 From: Andrew Morton Subject: Re: [PATCH v2] mm: Fix assertion mapping->nrpages == 0 in end_writeback() Message-Id: <20110620171833.411c96e0.akpm@linux-foundation.org> In-Reply-To: <1308152233-16919-1-git-send-email-jack@suse.cz> References: <1308152233-16919-1-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, Miklos Szeredi , Jay , Miklos Szeredi On Wed, 15 Jun 2011 17:37:13 +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 doing a reliable check of mapping->nrpages under > mapping->tree_lock in end_writeback(). > > Analyzed by Jay , lost in LKML, and dug > out by Miklos Szeredi . > > CC: Jay > CC: Miklos Szeredi > Signed-off-by: Jan Kara > --- > fs/inode.c | 7 +++++++ > include/linux/fs.h | 1 + > mm/truncate.c | 5 +++++ > 3 files changed, 13 insertions(+), 0 deletions(-) > > Andrew, does this look better? spose so. > diff --git a/fs/inode.c b/fs/inode.c > index 33c963d..1133cb0 100644 > --- a/fs/inode.c > +++ b/fs/inode.c > @@ -467,7 +467,14 @@ EXPORT_SYMBOL(remove_inode_hash); > void end_writeback(struct inode *inode) > { > might_sleep(); > + /* > + * We have to cycle tree_lock here because reclaim can be still in the > + * process of removing the last page (in __delete_from_page_cache()) > + * and we must not free mapping under it. > + */ > + spin_lock(&inode->i_data.tree_lock); > BUG_ON(inode->i_data.nrpages); > + spin_unlock(&inode->i_data.tree_lock); That's an expensive assertion. We might want to wrap all this in CONFIG_DEBUG_VM. Or we could do if (unlikely(inode->i_data.nrpages)) { /* comment goes here */ spin_lock(&inode->i_data.tree_lock); BUG_ON(inode->i_data.nrpages); spin_unlock(&inode->i_data.tree_lock); } -- 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