From 4ab78683c17d739c2a2077141dcf81a02b7fb57e Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Wed, 10 Mar 2010 15:22:34 -0800 Subject: cgroups: fix race between userspace and kernelspace Notify userspace about cgroup removing only after rmdir of cgroup directory to avoid race between userspace and kernelspace. eventfd are used to notify about two types of event: - control file-specific, like crossing memory threshold; - cgroup removing. To understand what really happen, userspace can check if the cgroup still exists. To avoid race beetween userspace and kernelspace we have to notify userspace about cgroup removing only after rmdir of cgroup directory. Signed-off-by: Kirill A. Shutemov Reviewed-by: KAMEZAWA Hiroyuki Cc: Paul Menage Acked-by: Li Zefan Cc: Balbir Singh Cc: Pavel Emelyanov Cc: Dan Malek Cc: Daisuke Nishimura Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/cgroup.c | 32 +++++++++++++++++--------------- 1 file changed, 17 insertions(+), 15 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index ea94984a3895..87441fc75663 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -795,28 +795,15 @@ static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb) static int cgroup_call_pre_destroy(struct cgroup *cgrp) { struct cgroup_subsys *ss; - struct cgroup_event *event, *tmp; int ret = 0; for_each_subsys(cgrp->root, ss) if (ss->pre_destroy) { ret = ss->pre_destroy(ss, cgrp); if (ret) - goto out; + break; } - /* - * Unregister events and notify userspace. - */ - spin_lock(&cgrp->event_list_lock); - list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) { - list_del(&event->list); - eventfd_signal(event->eventfd, 1); - schedule_work(&event->remove); - } - spin_unlock(&cgrp->event_list_lock); - -out: return ret; } @@ -3006,7 +2993,6 @@ static void cgroup_event_remove(struct work_struct *work) event->cft->unregister_event(cgrp, event->cft, event->eventfd); eventfd_ctx_put(event->eventfd); - remove_wait_queue(event->wqh, &event->wait); kfree(event); } @@ -3024,6 +3010,7 @@ static int cgroup_event_wake(wait_queue_t *wait, unsigned mode, unsigned long flags = (unsigned long)key; if (flags & POLLHUP) { + remove_wait_queue_locked(event->wqh, &event->wait); spin_lock(&cgrp->event_list_lock); list_del(&event->list); spin_unlock(&cgrp->event_list_lock); @@ -3472,6 +3459,7 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry) struct dentry *d; struct cgroup *parent; DEFINE_WAIT(wait); + struct cgroup_event *event, *tmp; int ret; /* the vfs holds both inode->i_mutex already */ @@ -3555,6 +3543,20 @@ again: set_bit(CGRP_RELEASABLE, &parent->flags); check_for_release(parent); + /* + * Unregister events and notify userspace. + * Notify userspace about cgroup removing only after rmdir of cgroup + * directory to avoid race between userspace and kernelspace + */ + spin_lock(&cgrp->event_list_lock); + list_for_each_entry_safe(event, tmp, &cgrp->event_list, list) { + list_del(&event->list); + remove_wait_queue(event->wqh, &event->wait); + eventfd_signal(event->eventfd, 1); + schedule_work(&event->remove); + } + spin_unlock(&cgrp->event_list_lock); + mutex_unlock(&cgroup_mutex); return 0; } -- cgit v1.2.3