cgroup: introduce cancel_attach()
Add cancel_attach() operation to struct cgroup_subsys. cancel_attach() can be used when can_attach() operation prepares something for the subsys, but we should rollback what can_attach() operation has prepared if attach task fails after we've succeeded in can_attach(). Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Acked-by: Li Zefan <lizf@cn.fujitsu.com> Reviewed-by: Paul Menage <menage@google.com> Cc: Balbir Singh <balbir@linux.vnet.ibm.com> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Linus Torvalds

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@@ -536,10 +536,21 @@ returns an error, this will abort the attach operation. If a NULL
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task is passed, then a successful result indicates that *any*
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unspecified task can be moved into the cgroup. Note that this isn't
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called on a fork. If this method returns 0 (success) then this should
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remain valid while the caller holds cgroup_mutex. If threadgroup is
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remain valid while the caller holds cgroup_mutex and it is ensured that either
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attach() or cancel_attach() will be called in future. If threadgroup is
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true, then a successful result indicates that all threads in the given
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thread's threadgroup can be moved together.
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void cancel_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
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struct task_struct *task, bool threadgroup)
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(cgroup_mutex held by caller)
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Called when a task attach operation has failed after can_attach() has succeeded.
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A subsystem whose can_attach() has some side-effects should provide this
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function, so that the subsytem can implement a rollback. If not, not necessary.
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This will be called only about subsystems whose can_attach() operation have
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succeeded.
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void attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
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struct cgroup *old_cgrp, struct task_struct *task,
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bool threadgroup)
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