From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ilya Dryomov Subject: [PATCH 1/3] rbd: fix rbd_dev_parent_get() when parent_overlap == 0 Date: Tue, 20 Jan 2015 15:41:07 +0300 Message-ID: <1421757669-38796-2-git-send-email-idryomov@redhat.com> References: <1421757669-38796-1-git-send-email-idryomov@redhat.com> Return-path: Received: from mail-wi0-f176.google.com ([209.85.212.176]:53976 "EHLO mail-wi0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751241AbbATMlr (ORCPT ); Tue, 20 Jan 2015 07:41:47 -0500 Received: by mail-wi0-f176.google.com with SMTP id em10so5153584wid.3 for ; Tue, 20 Jan 2015 04:41:46 -0800 (PST) In-Reply-To: <1421757669-38796-1-git-send-email-idryomov@redhat.com> Sender: ceph-devel-owner@vger.kernel.org List-ID: To: ceph-devel@vger.kernel.org Cc: Alex Elder The comment for rbd_dev_parent_get() said * We must get the reference before checking for the overlap to * coordinate properly with zeroing the parent overlap in * rbd_dev_v2_parent_info() when an image gets flattened. We * drop it again if there is no overlap. but the "drop it again if there is no overlap" part was missing from the implementation. This lead to absurd parent_ref values for images with parent_overlap == 0, as parent_ref was incremented for each img_request and virtually never decremented. Fix this by leveraging the fact that refresh path calls rbd_dev_v2_parent_info() under header_rwsem and use it for read in rbd_dev_parent_get(), instead of messing around with atomics. Get rid of barriers in rbd_dev_v2_parent_info() while at it - I don't see what they'd pair with now and I suspect we are in a pretty miserable situation as far as proper locking goes regardless. Cc: stable@vger.kernel.org # 3.11+ Signed-off-by: Ilya Dryomov --- drivers/block/rbd.c | 20 ++++++-------------- 1 file changed, 6 insertions(+), 14 deletions(-) diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c index 31fa00f0d707..2990a1c75159 100644 --- a/drivers/block/rbd.c +++ b/drivers/block/rbd.c @@ -2098,32 +2098,26 @@ static void rbd_dev_parent_put(struct rbd_device *rbd_dev) * If an image has a non-zero parent overlap, get a reference to its * parent. * - * We must get the reference before checking for the overlap to - * coordinate properly with zeroing the parent overlap in - * rbd_dev_v2_parent_info() when an image gets flattened. We - * drop it again if there is no overlap. - * * Returns true if the rbd device has a parent with a non-zero * overlap and a reference for it was successfully taken, or * false otherwise. */ static bool rbd_dev_parent_get(struct rbd_device *rbd_dev) { - int counter; + int counter = 0; if (!rbd_dev->parent_spec) return false; - counter = atomic_inc_return_safe(&rbd_dev->parent_ref); - if (counter > 0 && rbd_dev->parent_overlap) - return true; - - /* Image was flattened, but parent is not yet torn down */ + down_read(&rbd_dev->header_rwsem); + if (rbd_dev->parent_overlap) + counter = atomic_inc_return_safe(&rbd_dev->parent_ref); + up_read(&rbd_dev->header_rwsem); if (counter < 0) rbd_warn(rbd_dev, "parent reference overflow"); - return false; + return counter > 0; } /* @@ -4238,7 +4232,6 @@ static int rbd_dev_v2_parent_info(struct rbd_device *rbd_dev) */ if (rbd_dev->parent_overlap) { rbd_dev->parent_overlap = 0; - smp_mb(); rbd_dev_parent_put(rbd_dev); pr_info("%s: clone image has been flattened\n", rbd_dev->disk->disk_name); @@ -4284,7 +4277,6 @@ static int rbd_dev_v2_parent_info(struct rbd_device *rbd_dev) * treat it specially. */ rbd_dev->parent_overlap = overlap; - smp_mb(); if (!overlap) { /* A null parent_spec indicates it's the initial probe */ -- 1.9.3