Messages in this thread | | | Date | Mon, 30 Jun 2014 10:23:24 -0400 | From | Tejun Heo <> | Subject | Re: [PATCH v3 3/3] cgroup: fix a race between cgroup_mount() and cgroup_kill_sb() |
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Hello, Li.
I applied the three patches with some updates (mostly comments). Dynamic root management is turning out to be pretty ugly but I think we can clean it up a bit.
On Mon, Jun 30, 2014 at 11:50:59AM +0800, Li Zefan wrote: > @@ -1790,6 +1795,17 @@ out_free: > dentry = kernfs_mount(fs_type, flags, root->kf_root, &new_sb); > if (IS_ERR(dentry) || !new_sb) > cgroup_put(&root->cgrp); > + > + if (sb) { > + /* > + * On success kernfs_mount() returns with sb->s_umount held, > + * but kernfs_mount() also increases the superblock's refcnt, > + * so calling deactivate_super() to drop the refcnt we got when > + * looking up cgroup root won't acquire sb->s_umount again. > + */ > + WARN_ON(new_sb); > + deactivate_super(sb); > + }
So, @new_sb and @sb indicate the same conditions now. When we reuse an existing root, we always reuse its sb too which means that we at least no longer need the @new_sb ugliness. I actually kinda prefer it as this means that the ugliness is confined to one ugly function - kernfs_pin_sb() - instead of the generic kernfs_mount(). Can you please prepare patches to clean these up? I'll pull in for-3.16-fixes into for-3.17 and apply the cleanup on top.
Thanks!
-- tejun
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