From f9b4fb8dabf38fb456c97f01aace07cb6e7c1723 Mon Sep 17 00:00:00 2001 From: Miao Xie Date: Fri, 25 Jul 2008 01:47:22 -0700 Subject: [PATCH] cpusets: update task's cpus_allowed and mems_allowed after CPU/NODE offline/online The bug is that a task may run on the cpu/node which is not in its cpuset.cpus/ cpuset.mems. It can be reproduced by the following commands: ----------------------------------- # mkdir /dev/cpuset # mount -t cpuset xxx /dev/cpuset # mkdir /dev/cpuset/0 # echo 0-1 > /dev/cpuset/0/cpus # echo 0 > /dev/cpuset/0/mems # echo $$ > /dev/cpuset/0/tasks # echo 0 > /sys/devices/system/cpu/cpu1/online # echo 1 > /sys/devices/system/cpu/cpu1/online ----------------------------------- There is only CPU0 in cpuset.cpus, but the task in this cpuset runs on both CPU0 and CPU1. It is because the task's cpu_allowed didn't get updated after we did CPU offline/online manipulation. Similar for mem_allowed. This patch fixes this bug expect for root cpuset. Because there is a problem about root cpuset, in that whether it is necessary to update all the tasks in root cpuset or not after cpu/node offline/online. If updating, some kernel threads which is bound into a specified cpu will be unbound. If not updating, there is a bug in root cpuset. This bug is also caused by offline/online manipulation. For example, there is a dual-cpu machine. we create a sub cpuset in root cpuset and assign 1 to its cpus. And then we attach some tasks into this sub cpuset. After this, we offline CPU1. Now, the tasks in this new cpuset are moved into root cpuset automatically because there is no cpu in sub cpuset. Then we online CPU1, we find all the tasks which doesn't belong to root cpuset originally just run on CPU0. Maybe we need to add a flag in the task_struct to mark which task can't be unbound? Signed-off-by: Miao Xie Acked-by: Paul Jackson Cc: Li Zefan Cc: Paul Jackson Cc: Paul Menage Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/cpuset.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/cpuset.c b/kernel/cpuset.c index 7326d51eefe1..6eae6639e851 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -1851,6 +1851,7 @@ static void scan_for_empty_cpusets(const struct cpuset *root) struct cpuset *child; /* scans child cpusets of cp */ struct list_head queue; struct cgroup *cont; + nodemask_t oldmems; INIT_LIST_HEAD(&queue); @@ -1870,6 +1871,8 @@ static void scan_for_empty_cpusets(const struct cpuset *root) nodes_subset(cp->mems_allowed, node_states[N_HIGH_MEMORY])) continue; + oldmems = cp->mems_allowed; + /* Remove offline cpus and mems from this cpuset. */ mutex_lock(&callback_mutex); cpus_and(cp->cpus_allowed, cp->cpus_allowed, cpu_online_map); @@ -1881,6 +1884,10 @@ static void scan_for_empty_cpusets(const struct cpuset *root) if (cpus_empty(cp->cpus_allowed) || nodes_empty(cp->mems_allowed)) remove_tasks_in_empty_cpuset(cp); + else { + update_tasks_cpumask(cp); + update_tasks_nodemask(cp, &oldmems); + } } }