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blkcg: blkcg_css_alloc() should grab blkcg_pol_mutex while iterating blkcg_policy[]

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An entry in blkcg_policy[] is stable while there are non-bypassing
in-flight IOs on a request_queue which has the policy activated.  This
is why most derefs of blkcg_policy[] don't need explicit locking;
however, blkcg_css_alloc() isn't invoked from IO path and thus doesn't
have this protection and may race policies being added and removed.

Fix it by adding explicit blkcg_pol_mutex protection around
blkcg_policy[] iteration in blkcg_css_alloc().

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: e48453c386 ("block, cgroup: implement policy-specific per-blkcg data")
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Tejun Heo 2015-07-09 16:39:48 -04:00 committed by Jens Axboe
parent 838f13bf4b
commit 144232b342
1 changed files with 4 additions and 0 deletions
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4
block/blk-cgroup.c
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@ -844,6 +844,8 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
goto free_blkcg;
}
mutex_lock(&blkcg_pol_mutex);
for (i = 0; i < BLKCG_MAX_POLS ; i++) {
struct blkcg_policy *pol = blkcg_policy[i];
struct blkcg_policy_data *cpd;
@ -860,6 +862,7 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
BUG_ON(blkcg->pd[i]);
cpd = kzalloc(pol->cpd_size, GFP_KERNEL);
if (!cpd) {
mutex_unlock(&blkcg_pol_mutex);
ret = ERR_PTR(-ENOMEM);
goto free_pd_blkcg;
}
@ -868,6 +871,7 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
pol->cpd_init_fn(blkcg);
}
mutex_unlock(&blkcg_pol_mutex);
done:
spin_lock_init(&blkcg->lock);
INIT_RADIX_TREE(&blkcg->blkg_tree, GFP_ATOMIC);