From ae43e9d05eb4bd324155292f889fbd001c4faea8 Mon Sep 17 00:00:00 2001 From: Ilya Dryomov Date: Mon, 19 Jan 2015 18:13:43 +0300 Subject: [PATCH] rbd: fix rbd_dev_parent_get() when parent_overlap == 0 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 Reviewed-by: Josh Durgin Reviewed-by: Alex Elder --- 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 3ec85dfce124..d511ecb35144 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; } /* @@ -4239,7 +4233,6 @@ 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); @@ -4285,7 +4278,6 @@ 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 */ -- 2.11.0