Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932438AbaKMJPf (ORCPT ); Thu, 13 Nov 2014 04:15:35 -0500 Received: from ozlabs.org ([103.22.144.67]:41974 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932098AbaKMJP3 (ORCPT ); Thu, 13 Nov 2014 04:15:29 -0500 Date: Thu, 13 Nov 2014 20:15:23 +1100 From: Paul Mackerras To: Linus Torvalds , Al Viro Cc: linux-kernel@vger.kernel.org Subject: [PATCH] Fix thinko in iov_iter_single_seg_count Message-ID: <20141113091523.GC26910@iris.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The branches of the if (i->type & ITER_BVEC) statement in iov_iter_single_seg_count() are the wrong way around; if ITER_BVEC is clear then we use i->bvec, when we should be using i->iov. This fixes it. In my case, the symptom that this caused was that a KVM guest doing filesystem operations on a virtual disk would result in one of qemu's threads on the host going into an infinite loop in generic_perform_write(). The loop would hit the copied == 0 case and call iov_iter_single_seg_count() to reduce the number of bytes to try to process, but because of the error, iov_iter_single_seg_count() would just return i->count and the loop made no progress and continued forever. Cc: stable@vger.kernel.org # 3.16+ Signed-off-by: Paul Mackerras --- diff --git a/mm/iov_iter.c b/mm/iov_iter.c index eafcf60..e34a3cb 100644 --- a/mm/iov_iter.c +++ b/mm/iov_iter.c @@ -911,9 +911,9 @@ size_t iov_iter_single_seg_count(const struct iov_iter *i) if (i->nr_segs == 1) return i->count; else if (i->type & ITER_BVEC) - return min(i->count, i->iov->iov_len - i->iov_offset); - else return min(i->count, i->bvec->bv_len - i->iov_offset); + else + return min(i->count, i->iov->iov_len - i->iov_offset); } EXPORT_SYMBOL(iov_iter_single_seg_count); -- 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/