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authorTejun Heo <tj@kernel.org>2012-03-05 13:15:00 -0800
committerJens Axboe <axboe@kernel.dk>2012-03-06 21:27:22 +0100
commit72e06c255181537d0b3e1f657a9ed81655d745b1 (patch)
treeeb656df2ad23a7709b4e9fe58f1dabdc32be9ae9 /block/elevator.c
parent6ecf23afab13c39d3bb0e2d826d0984b0dd53733 (diff)
blkcg: shoot down blkio_groups on elevator switch
Elevator switch may involve changes to blkcg policies. Implement shoot down of blkio_groups. Combined with the previous bypass updates, the end goal is updating blkcg core such that it can ensure that blkcg's being affected become quiescent and don't have any per-blkg data hanging around before commencing any policy updates. Until queues are made aware of the policies that applies to them, as an interim step, all per-policy blkg data will be shot down. * blk-throtl doesn't need this change as it can't be disabled for a live queue; however, update it anyway as the scheduled blkg unification requires this behavior change. This means that blk-throtl configuration will be unnecessarily lost over elevator switch. This oddity will be removed after blkcg learns to associate individual policies with request_queues. * blk-throtl dosen't shoot down root_tg. This is to ease transition. Unified blkg will always have persistent root group and not shooting down root_tg for now eases transition to that point by avoiding having to update td->root_tg and is safe as blk-throtl can never be disabled -v2: Vivek pointed out that group list is not guaranteed to be empty on return from clear function if it raced cgroup removal and lost. Fix it by waiting a bit and retrying. This kludge will soon be removed once locking is updated such that blkg is never in limbo state between blkcg and request_queue locks. blk-throtl no longer shoots down root_tg to avoid breaking td->root_tg. Also, Nest queue_lock inside blkio_list_lock not the other way around to avoid introduce possible deadlock via blkcg lock. -v3: blkcg_clear_queue() repositioned and renamed to blkg_destroy_all() to increase consistency with later changes. cfq_clear_queue() updated to check q->elevator before dereferencing it to avoid NULL dereference on not fully initialized queues (used by later change). Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/elevator.c')
-rw-r--r--block/elevator.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/block/elevator.c b/block/elevator.c
index 0bdea0ed03a..8c7561fd2c7 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -38,6 +38,7 @@
#include <trace/events/block.h>
#include "blk.h"
+#include "blk-cgroup.h"
static DEFINE_SPINLOCK(elv_list_lock);
static LIST_HEAD(elv_list);
@@ -894,6 +895,8 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
ioc_clear_queue(q);
spin_unlock_irq(q->queue_lock);
+ blkg_destroy_all(q);
+
/* allocate, init and register new elevator */
err = -ENOMEM;
q->elevator = elevator_alloc(q, new_e);