Messages in this thread | | | Date | Fri, 23 Jan 2009 19:36:53 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] cgroup: Fix root_count when mount fails due to busy subsystem |
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* Paul Menage <menage@google.com> wrote:
> 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().
Which exact call chain is that?
> 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.
Agreed, that's not an improvement.
> For 2.6.29, we should fix this by reverting the broken part of the patch > that made it into 2.6.29-rcX
Agreed too - i withdraw my objection.
Nevertheless my observation remains: kernel/cgroup.c has a complex looking error paths which should be cleaned up. (independently of this issue)
Ingo
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