Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965681AbbLPPeJ (ORCPT ); Wed, 16 Dec 2015 10:34:09 -0500 Received: from mx2.suse.de ([195.135.220.15]:49323 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932664AbbLPPeH (ORCPT ); Wed, 16 Dec 2015 10:34:07 -0500 Date: Wed, 16 Dec 2015 16:34:04 +0100 From: Jan Kara To: Abhi Das Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Bob Peterson Subject: Re: [RFC v2 PATCH] fs: __generic_file_splice_read retry lookup on AOP_TRUNCATED_PAGE Message-ID: <20151216153404.GC16918@quack.suse.cz> References: <1450194205-44587-1-git-send-email-adas@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1450194205-44587-1-git-send-email-adas@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2850 Lines: 76 On Tue 15-12-15 09:43:25, Abhi Das wrote: > During testing, I discovered that __generic_file_splice_read() returns > 0 (EOF) when aops->readpage fails with AOP_TRUNCATED_PAGE on the first > page of a single/multi-page splice read operation. This EOF return code > causes the userspace test to (correctly) report a zero-length read error > when it was expecting otherwise. > > The current strategy of returning a partial non-zero read when ->readpage > returns AOP_TRUNCATED_PAGE works only when the failed page is not the > first of the lot being processed. > > This patch attempts to retry lookup and call ->readpage again on pages > that had previously failed with AOP_TRUNCATED_PAGE. With this patch, my > tests pass and I haven't noticed any unwanted side effects. > > This version fixes a return code issue pointed out by Bob Peterson. > > Signed-off-by: Abhi Das > Cc: Bob Peterson > --- > fs/splice.c | 13 +++++++------ > 1 file changed, 7 insertions(+), 6 deletions(-) > > diff --git a/fs/splice.c b/fs/splice.c > index 801c21c..365cd2a 100644 > --- a/fs/splice.c > +++ b/fs/splice.c > @@ -387,6 +387,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos, > spd.nr_pages = 0; > for (page_nr = 0; page_nr < nr_pages; page_nr++) { > unsigned int this_len; > + int retries = 0; > > if (!len) > break; > @@ -415,6 +416,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos, > */ > if (!page->mapping) { > unlock_page(page); > +retry_lookup: > page = find_or_create_page(mapping, index, > mapping_gfp_mask(mapping)); > > @@ -439,14 +441,13 @@ __generic_file_splice_read(struct file *in, loff_t *ppos, > error = mapping->a_ops->readpage(in, page); > if (unlikely(error)) { > /* > - * We really should re-lookup the page here, > - * but it complicates things a lot. Instead > - * lets just do what we already stored, and > - * we'll get it the next time we are called. > + * Re-lookup the page > */ > - if (error == AOP_TRUNCATED_PAGE) > + if (error == AOP_TRUNCATED_PAGE) { > error = 0; > - > + if (retries++ < 3) > + goto retry_lookup; > + } I don't like this retry-three-times loop. That is still leaving the possibility of 0 return just much less likely (so it will lead to even weirder and harded to debug failures). IMO we should just terminate the loop like we did previously if spd.nr_pages > 0 and we retry indefinitely if it is the first page that failed to read. Honza -- Jan Kara SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/