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Date: Tue, 22 Feb 2011 12:30:14 -0800 (PST)
From: David Rientjes <rientjes@...gle.com>
To: Li Zefan <lizf@...fujitsu.com>
cc: Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>,
Paul Menage <menage@...gle.com>, miaox@...fujitsu.com,
linux-mm@...ck.org
Subject: Re: [PATCH 3/4] cpuset: Fix unchecked calls to NODEMASK_ALLOC()
On Tue, 22 Feb 2011, Li Zefan wrote:
> [PATCH 3/4] cpuset: Fix unchecked calls to NODEMASK_ALLOC()
>
> Those functions that use NODEMASK_ALLOC() can't propogate errno
> to users, so might fail silently.
>
> Fix it by using one static nodemask_t variable for each function, and
> those variables are protected by cgroup_mutex.
>
I think there would also be incentive to do the same thing for
update_nodemask() even though its caller can handle -ENOMEM. Imagine
current being out of memory and the NODEMASK_ALLOC() subsequently failing
because it is oom yet it may be trying to give itself more memory. It's
also protected by cgroup_mutex so the only thing we're sacrificing is 8
bytes on the defconfig and 256 bytes even with CONFIG_NODES_SHIFT == 10.
On machines that large, this seems like an acceptable cost to ensure we
can give ourselves more memory :)
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
> kernel/cpuset.c | 50 ++++++++++++++++----------------------------------
> 1 files changed, 16 insertions(+), 34 deletions(-)
>
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 8fef8c6..073ce91 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -1015,17 +1015,12 @@ static void cpuset_change_nodemask(struct task_struct *p,
> struct cpuset *cs;
> int migrate;
> const nodemask_t *oldmem = scan->data;
> - NODEMASK_ALLOC(nodemask_t, newmems, GFP_KERNEL);
> -
> - if (!newmems)
> - return;
> + static nodemask_t newmems; /* protected by cgroup_mutex */
>
> cs = cgroup_cs(scan->cg);
> - guarantee_online_mems(cs, newmems);
> -
> - cpuset_change_task_nodemask(p, newmems);
> + guarantee_online_mems(cs, &newmems);
The newmems nodemask is going to be persistant across calls since it is
static, so we have to be careful that nothing depends on it being
NODE_MASK_NONE. Indeed, NODEMASK_ALLOC() with just GFP_KERNEL doesn't
guarantee anything different. guarantee_online_mems() sets the nodemask,
so this looks good.
>
> - NODEMASK_FREE(newmems);
> + cpuset_change_task_nodemask(p, &newmems);
>
> mm = get_task_mm(p);
> if (!mm)
> @@ -1438,41 +1433,35 @@ static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
> struct mm_struct *mm;
> struct cpuset *cs = cgroup_cs(cont);
> struct cpuset *oldcs = cgroup_cs(oldcont);
> - NODEMASK_ALLOC(nodemask_t, to, GFP_KERNEL);
> -
> - if (to == NULL)
> - goto alloc_fail;
> + static nodemask_t to; /* protected by cgroup_mutex */
>
> if (cs == &top_cpuset) {
> cpumask_copy(cpus_attach, cpu_possible_mask);
> } else {
> guarantee_online_cpus(cs, cpus_attach);
> }
> - guarantee_online_mems(cs, to);
> + guarantee_online_mems(cs, &to);
>
> /* do per-task migration stuff possibly for each in the threadgroup */
> - cpuset_attach_task(tsk, to, cs);
> + cpuset_attach_task(tsk, &to, cs);
> if (threadgroup) {
> struct task_struct *c;
> rcu_read_lock();
> list_for_each_entry_rcu(c, &tsk->thread_group, thread_group) {
> - cpuset_attach_task(c, to, cs);
> + cpuset_attach_task(c, &to, cs);
> }
> rcu_read_unlock();
> }
>
> /* change mm; only needs to be done once even if threadgroup */
> - *to = cs->mems_allowed;
> + to = cs->mems_allowed;
> mm = get_task_mm(tsk);
> if (mm) {
> - mpol_rebind_mm(mm, to);
> + mpol_rebind_mm(mm, &to);
> if (is_memory_migrate(cs))
> - cpuset_migrate_mm(mm, &oldcs->mems_allowed, to);
> + cpuset_migrate_mm(mm, &oldcs->mems_allowed, &to);
> mmput(mm);
> }
> -
> -alloc_fail:
> - NODEMASK_FREE(to);
> }
>
> /* The various types of files and directories in a cpuset file system */
> @@ -2051,10 +2040,7 @@ static void scan_for_empty_cpusets(struct cpuset *root)
> struct cpuset *cp; /* scans cpusets being updated */
> struct cpuset *child; /* scans child cpusets of cp */
> struct cgroup *cont;
> - NODEMASK_ALLOC(nodemask_t, oldmems, GFP_KERNEL);
> -
> - if (oldmems == NULL)
> - return;
> + static nodemask_t oldmems; /* protected by cgroup_mutex */
>
> list_add_tail((struct list_head *)&root->stack_list, &queue);
>
> @@ -2071,7 +2057,7 @@ static void scan_for_empty_cpusets(struct cpuset *root)
> nodes_subset(cp->mems_allowed, node_states[N_HIGH_MEMORY]))
> continue;
>
> - *oldmems = cp->mems_allowed;
> + oldmems = cp->mems_allowed;
>
> /* Remove offline cpus and mems from this cpuset. */
> mutex_lock(&callback_mutex);
> @@ -2087,10 +2073,9 @@ static void scan_for_empty_cpusets(struct cpuset *root)
> remove_tasks_in_empty_cpuset(cp);
> else {
> update_tasks_cpumask(cp, NULL);
> - update_tasks_nodemask(cp, oldmems, NULL);
> + update_tasks_nodemask(cp, &oldmems, NULL);
> }
> }
> - NODEMASK_FREE(oldmems);
> }
>
> /*
> @@ -2132,19 +2117,16 @@ void cpuset_update_active_cpus(void)
> static int cpuset_track_online_nodes(struct notifier_block *self,
> unsigned long action, void *arg)
> {
> - NODEMASK_ALLOC(nodemask_t, oldmems, GFP_KERNEL);
> -
> - if (oldmems == NULL)
> - return NOTIFY_DONE;
> + static nodemask_t oldmems; /* protected by cgroup_mutex */
>
> cgroup_lock();
> switch (action) {
> case MEM_ONLINE:
> - *oldmems = top_cpuset.mems_allowed;
> + oldmems = top_cpuset.mems_allowed;
> mutex_lock(&callback_mutex);
> top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
> mutex_unlock(&callback_mutex);
> - update_tasks_nodemask(&top_cpuset, oldmems, NULL);
> + update_tasks_nodemask(&top_cpuset, &oldmems, NULL);
> break;
> case MEM_OFFLINE:
> /*
The NODEMASK_FREE() wasn't removed from cpuset_track_online_nodes().
After that's fixed:
Acked-by: David Rientjes <rientjes@...gle.com>
--
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