From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 015CE21163702 for ; Mon, 8 Oct 2018 06:42:32 -0700 (PDT) Date: Mon, 8 Oct 2018 15:42:30 +0200 From: Jan Kara Subject: Re: [PATCH v2] filesystem-dax: Fix dax_layout_busy_page() livelock Message-ID: <20181008134230.GC21682@quack2.suse.cz> References: <153889193718.3143179.3432479794012686784.stgit@dwillia2-desk3.amr.corp.intel.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <153889193718.3143179.3432479794012686784.stgit@dwillia2-desk3.amr.corp.intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Dan Williams Cc: Jan Kara , linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org, Matthew Wilcox , stable@vger.kernel.org, Ross Zwisler , linux-fsdevel@vger.kernel.org List-ID: On Sat 06-10-18 22:59:56, Dan Williams wrote: > In the presence of multi-order entries the typical > pagevec_lookup_entries() pattern may loop forever: > > while (index < end && pagevec_lookup_entries(&pvec, mapping, index, > min(end - index, (pgoff_t)PAGEVEC_SIZE), > indices)) { > ... > for (i = 0; i < pagevec_count(&pvec); i++) { > index = indices[i]; > ... > } > index++; /* BUG */ > } > > The loop updates 'index' for each index found and then increments to the > next possible page to continue the lookup. However, if the last entry in > the pagevec is multi-order then the next possible page index is more > than 1 page away. Fix this locally for the filesystem-dax case by > checking for dax-multi-order entries. Going forward new users of > multi-order entries need to be similarly careful, or we need a generic > way to report the page increment in the radix iterator. > > Fixes: 5fac7408d828 ("mm, fs, dax: handle layout changes to pinned dax...") > Cc: > Cc: Jan Kara > Cc: Ross Zwisler > Cc: Matthew Wilcox > Signed-off-by: Dan Williams > --- > Changes in v2: > * Only update nr_pages if the last entry in the pagevec is multi-order. > > fs/dax.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) Thanks for fixing this up! It is somewhat ugly but nicer fixes would be more intrusive so I agree with this approach for the ease of backporting and let's clean up the iteration code later. Feel free to add: Reviewed-by: Jan Kara Honza > > diff --git a/fs/dax.c b/fs/dax.c > index 4becbf168b7f..0fb270f0a0ef 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -666,6 +666,8 @@ struct page *dax_layout_busy_page(struct address_space *mapping) > while (index < end && pagevec_lookup_entries(&pvec, mapping, index, > min(end - index, (pgoff_t)PAGEVEC_SIZE), > indices)) { > + pgoff_t nr_pages = 1; > + > for (i = 0; i < pagevec_count(&pvec); i++) { > struct page *pvec_ent = pvec.pages[i]; > void *entry; > @@ -680,8 +682,15 @@ struct page *dax_layout_busy_page(struct address_space *mapping) > > xa_lock_irq(&mapping->i_pages); > entry = get_unlocked_mapping_entry(mapping, index, NULL); > - if (entry) > + if (entry) { > page = dax_busy_page(entry); > + /* > + * Account for multi-order entries at > + * the end of the pagevec. > + */ > + if (i + 1 >= pagevec_count(&pvec)) > + nr_pages = 1UL << dax_radix_order(entry); > + } > put_unlocked_mapping_entry(mapping, index, entry); > xa_unlock_irq(&mapping->i_pages); > if (page) > @@ -696,7 +705,7 @@ struct page *dax_layout_busy_page(struct address_space *mapping) > */ > pagevec_remove_exceptionals(&pvec); > pagevec_release(&pvec); > - index++; > + index += nr_pages; > > if (page) > break; > -- Jan Kara SUSE Labs, CR _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm