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cgroup avoid permanent sleep at rmdir

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After commit ec64f51545 ("cgroup: fix
frequent -EBUSY at rmdir"), cgroup's rmdir (especially against memcg)
doesn't return -EBUSY by temporary ref counts.  That commit expects all
refs after pre_destroy() is temporary but...it wasn't.  Then, rmdir can
wait permanently.  This patch tries to fix that and change followings.

 - set CGRP_WAIT_ON_RMDIR flag before pre_destroy().
 - clear CGRP_WAIT_ON_RMDIR flag when the subsys finds racy case.
   if there are sleeping ones, wakes them up.
 - rmdir() sleeps only when CGRP_WAIT_ON_RMDIR flag is set.

Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reported-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by: Paul Menage <menage@google.com>
Acked-by: Balbir Sigh <balbir@linux.vnet.ibm.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KAMEZAWA Hiroyuki
2009-07-29 15:04:06 -07:00
committed by Linus Torvalds
parent f0d83679a8
commit 887032670d
3 changed files with 75 additions and 20 deletions
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17
include/linux/cgroup.h
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@ -362,6 +362,23 @@ int cgroup_task_count(const struct cgroup *cgrp);
/* Return true if cgrp is a descendant of the task's cgroup */
int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task);
/*
* When the subsys has to access css and may add permanent refcnt to css,
* it should take care of racy conditions with rmdir(). Following set of
* functions, is for stop/restart rmdir if necessary.
* Because these will call css_get/put, "css" should be alive css.
*
* cgroup_exclude_rmdir();
* ...do some jobs which may access arbitrary empty cgroup
* cgroup_release_and_wakeup_rmdir();
*
* When someone removes a cgroup while cgroup_exclude_rmdir() holds it,
* it sleeps and cgroup_release_and_wakeup_rmdir() will wake him up.
*/
void cgroup_exclude_rmdir(struct cgroup_subsys_state *css);
void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css);
/*
* Control Group subsystem type.
* See Documentation/cgroups/cgroups.txt for details