From e15693ef18e13e3e6bffe891fe140f18b8ff6d07 Mon Sep 17 00:00:00 2001 From: Toshiaki Makita Date: Tue, 26 Aug 2014 20:56:36 +0900 Subject: [PATCH] cfq-iosched: Fix wrong children_weight calculation cfq_group_service_tree_add() is applying new_weight at the beginning of the function via cfq_update_group_weight(). This actually allows weight to change between adding it to and subtracting it from children_weight, and triggers WARN_ON_ONCE() in cfq_group_service_tree_del(), or even causes oops by divide error during vfr calculation in cfq_group_service_tree_add(). The detailed scenario is as follows: 1. Create blkio cgroups X and Y as a child of X. Set X's weight to 500 and perform some I/O to apply new_weight. This X's I/O completes before starting Y's I/O. 2. Y starts I/O and cfq_group_service_tree_add() is called with Y. 3. cfq_group_service_tree_add() walks up the tree during children_weight calculation and adds parent X's weight (500) to children_weight of root. children_weight becomes 500. 4. Set X's weight to 1000. 5. X starts I/O and cfq_group_service_tree_add() is called with X. 6. cfq_group_service_tree_add() applies its new_weight (1000). 7. I/O of Y completes and cfq_group_service_tree_del() is called with Y. 8. I/O of X completes and cfq_group_service_tree_del() is called with X. 9. cfq_group_service_tree_del() subtracts X's weight (1000) from children_weight of root. children_weight becomes -500. This triggers WARN_ON_ONCE(). 10. Set X's weight to 500. 11. X starts I/O and cfq_group_service_tree_add() is called with X. 12. cfq_group_service_tree_add() applies its new_weight (500) and adds it to children_weight of root. children_weight becomes 0. Calcularion of vfr triggers oops by divide error. weight should be updated right before adding it to children_weight. Reported-by: Ruki Sekiya Signed-off-by: Toshiaki Makita Acked-by: Tejun Heo Cc: stable@vger.kernel.org Signed-off-by: Jens Axboe --- block/cfq-iosched.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index cadc37841744..d7494637c5db 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1275,12 +1275,16 @@ __cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg) static void cfq_update_group_weight(struct cfq_group *cfqg) { - BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node)); - if (cfqg->new_weight) { cfqg->weight = cfqg->new_weight; cfqg->new_weight = 0; } +} + +static void +cfq_update_group_leaf_weight(struct cfq_group *cfqg) +{ + BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node)); if (cfqg->new_leaf_weight) { cfqg->leaf_weight = cfqg->new_leaf_weight; @@ -1299,7 +1303,7 @@ cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg) /* add to the service tree */ BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node)); - cfq_update_group_weight(cfqg); + cfq_update_group_leaf_weight(cfqg); __cfq_group_service_tree_add(st, cfqg); /* @@ -1323,6 +1327,7 @@ cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg) */ while ((parent = cfqg_parent(pos))) { if (propagate) { + cfq_update_group_weight(pos); propagate = !parent->nr_active++; parent->children_weight += pos->weight; } -- 2.20.1