Messages in this thread | | | Date | Fri, 23 Jan 2009 10:32:09 -0800 | Subject | Re: [PATCH] cgroup: Fix root_count when mount fails due to busy subsystem | From | Paul Menage <> |
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On Fri, Jan 23, 2009 at 10:10 AM, Ingo Molnar <mingo@elte.hu> wrote: > > * Paul Menage <menage@google.com> wrote: > >> cgroup: Fix root_count when mount fails due to busy subsystem >> >> root_count was being incremented in cgroup_get_sb() after all error >> checking was complete, but decremented in cgroup_kill_sb(), which can be >> called on a superblock that we gave up on due to an error. This patch >> changes cgroup_kill_sb() to only decrement root_count if the root was >> previously linked into the list of roots. > > i'm wondering, what happens in the buggy case: does cgroup_kill_sb() get > called twice (if yes, why?),
No.
> or do we call cgroup_kill_sb() on a not yet > added sb and hence root_count has not been elevated yet?
Right.
> (if yes, which > codepath does this?)
It's via the call to deactivate_super().
The code could be restructured such that:
- we don't set sb->s_fs_info until we've linked the new root into the root_list - do any necessary cleanup for a failed root in cgroup_get_sb() - have cgroup_kill_sb() handle either no root or a fully-initialized root
But then you're replacing "only decrement root_count if root was linked in to list" with "only do root cleanup if root was atached to sb" in cgroup_kill_sb(). I don't see that one is much cleaner than the other.
For 2.6.29, we should fix this by reverting the broken part of the patch that made it into 2.6.29-rcX
Paul
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