On Wed 28-08-13 23:03:54, David Rientjes wrote:
> A shared buffer is currently used for the name of the oom memcg and the
> memcg of the killed process. There is no serialization of memcg oom
> kills, so this buffer can easily be overwritten if there is a concurrent
> oom kill in another memcg.
Right.
> This patch stores the names of the memcgs directly in struct mem_cgroup.
I do not like to make every mem_cgroup larger even if it never sees an
OOM.
Wouldn't it be much easier to add a new lock (memcg_oom_info_lock) inside
mem_cgroup_print_oom_info instead? This would have a nice side effect
that parallel memcg oom kill messages wouldn't interleave.
> This allows it to be printed anytime during the oom kill without fearing
> that it will change or become corrupted. It also ensures that the name
> of the memcg that is oom and the memcg of the killed process are the same
> even if renamed at the same time.
>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
> mm/memcontrol.c | 49 +++++++++++++++++++++++--------------------------
> 1 file changed, 23 insertions(+), 26 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -83,6 +83,8 @@ static int really_do_swap_account __initdata = 0;
> #define do_swap_account 0
> #endif
>
> +/* First 128 bytes of memcg name should be unique */
> +#define MEM_CGROUP_STORE_NAME_LEN 128
>
> static const char * const mem_cgroup_stat_names[] = {
> "cache",
> @@ -247,6 +249,9 @@ struct mem_cgroup {
> /* OOM-Killer disable */
> int oom_kill_disable;
>
> + /* name of memcg for display purposes only */
> + char name[MEM_CGROUP_STORE_NAME_LEN];
> +
> /* set when res.limit == memsw.limit */
> bool memsw_is_minimum;
>
> @@ -1538,27 +1543,22 @@ static void move_unlock_mem_cgroup(struct mem_cgroup *memcg,
> */
> void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
> {
> + struct mem_cgroup *task_memcg;
> + struct mem_cgroup *iter;
> struct cgroup *task_cgrp;
> struct cgroup *mem_cgrp;
> - /*
> - * Need a buffer in BSS, can't rely on allocations. The code relies
> - * on the assumption that OOM is serialized for memory controller.
> - * If this assumption is broken, revisit this code.
> - */
> - static char memcg_name[PATH_MAX];
> int ret;
> - struct mem_cgroup *iter;
> unsigned int i;
>
> if (!p)
> return;
>
> rcu_read_lock();
> -
> - mem_cgrp = memcg->css.cgroup;
> + task_memcg = mem_cgroup_from_task(p);
> task_cgrp = task_cgroup(p, mem_cgroup_subsys_id);
> + mem_cgrp = memcg->css.cgroup;
>
> - ret = cgroup_path(task_cgrp, memcg_name, PATH_MAX);
> + ret = cgroup_path(task_cgrp, task_memcg->name, MEM_CGROUP_STORE_NAME_LEN);
> if (ret < 0) {
> /*
> * Unfortunately, we are unable to convert to a useful name
> @@ -1567,24 +1567,20 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
> rcu_read_unlock();
> goto done;
> }
> - rcu_read_unlock();
>
> - pr_info("Task in %s killed", memcg_name);
> + if (task_memcg != memcg) {
> + ret = cgroup_path(mem_cgrp, memcg->name, MEM_CGROUP_STORE_NAME_LEN);
> + if (ret < 0) {
> + rcu_read_unlock();
> + goto done;
> + }
> + } else
> + strncpy(memcg->name, task_memcg->name, MEM_CGROUP_STORE_NAME_LEN);
>
> - rcu_read_lock();
> - ret = cgroup_path(mem_cgrp, memcg_name, PATH_MAX);
> - if (ret < 0) {
> - rcu_read_unlock();
> - goto done;
> - }
> + pr_info("Task in %s killed as a result of limit of %s\n",
> + task_memcg->name, memcg->name);
> rcu_read_unlock();
> -
> - /*
> - * Continues from above, so we don't need an KERN_ level
> - */
> - pr_cont(" as a result of limit of %s\n", memcg_name);
> done:
> -
> pr_info("memory: usage %llukB, limit %llukB, failcnt %llu\n",
> res_counter_read_u64(&memcg->res, RES_USAGE) >> 10,
> res_counter_read_u64(&memcg->res, RES_LIMIT) >> 10,
> @@ -1602,9 +1598,10 @@ done:
> pr_info("Memory cgroup stats");
>
> rcu_read_lock();
> - ret = cgroup_path(iter->css.cgroup, memcg_name, PATH_MAX);
> + ret = cgroup_path(iter->css.cgroup, iter->name,
> + MEM_CGROUP_STORE_NAME_LEN);
> if (!ret)
> - pr_cont(" for %s", memcg_name);
> + pr_cont(" for %s", iter->name);
> rcu_read_unlock();
> pr_cont(":");
>
--
Michal Hocko
SUSE Labs
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