From da39da3a54fed88e29024f2f1f6cd7357cd03a44 Mon Sep 17 00:00:00 2001 From: David Rientjes Date: Thu, 5 Nov 2015 18:48:05 -0800 Subject: mm, oom: remove task_lock protecting comm printing The oom killer takes task_lock() in a couple of places solely to protect printing the task's comm. A process's comm, including current's comm, may change due to /proc/pid/comm or PR_SET_NAME. The comm will always be NULL-terminated, so the worst race scenario would only be during update. We can tolerate a comm being printed that is in the middle of an update to avoid taking the lock. Other locations in the kernel have already dropped task_lock() when printing comm, so this is consistent. Signed-off-by: David Rientjes Suggested-by: Oleg Nesterov Cc: Michal Hocko Cc: Vladimir Davydov Cc: Sergey Senozhatsky Acked-by: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/cpuset.h | 4 ++-- kernel/cpuset.c | 14 +++++++------- mm/oom_kill.c | 8 +------- 3 files changed, 10 insertions(+), 16 deletions(-) diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h index 1b357997cac5..5a1311942358 100644 --- a/include/linux/cpuset.h +++ b/include/linux/cpuset.h @@ -93,7 +93,7 @@ extern int current_cpuset_is_being_rebound(void); extern void rebuild_sched_domains(void); -extern void cpuset_print_task_mems_allowed(struct task_struct *p); +extern void cpuset_print_current_mems_allowed(void); /* * read_mems_allowed_begin is required when making decisions involving @@ -219,7 +219,7 @@ static inline void rebuild_sched_domains(void) partition_sched_domains(1, NULL, NULL); } -static inline void cpuset_print_task_mems_allowed(struct task_struct *p) +static inline void cpuset_print_current_mems_allowed(void) { } diff --git a/kernel/cpuset.c b/kernel/cpuset.c index f0acff0f66c9..9ef59a37c190 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -2598,22 +2598,22 @@ int cpuset_mems_allowed_intersects(const struct task_struct *tsk1, } /** - * cpuset_print_task_mems_allowed - prints task's cpuset and mems_allowed - * @tsk: pointer to task_struct of some task. + * cpuset_print_current_mems_allowed - prints current's cpuset and mems_allowed * - * Description: Prints @task's name, cpuset name, and cached copy of its + * Description: Prints current's name, cpuset name, and cached copy of its * mems_allowed to the kernel log. */ -void cpuset_print_task_mems_allowed(struct task_struct *tsk) +void cpuset_print_current_mems_allowed(void) { struct cgroup *cgrp; rcu_read_lock(); - cgrp = task_cs(tsk)->css.cgroup; - pr_info("%s cpuset=", tsk->comm); + cgrp = task_cs(current)->css.cgroup; + pr_info("%s cpuset=", current->comm); pr_cont_cgroup_name(cgrp); - pr_cont(" mems_allowed=%*pbl\n", nodemask_pr_args(&tsk->mems_allowed)); + pr_cont(" mems_allowed=%*pbl\n", + nodemask_pr_args(¤t->mems_allowed)); rcu_read_unlock(); } diff --git a/mm/oom_kill.c b/mm/oom_kill.c index c170d9f0a158..58f3d2748ced 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -377,13 +377,11 @@ static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask) static void dump_header(struct oom_control *oc, struct task_struct *p, struct mem_cgroup *memcg) { - task_lock(current); pr_warning("%s invoked oom-killer: gfp_mask=0x%x, order=%d, " "oom_score_adj=%hd\n", current->comm, oc->gfp_mask, oc->order, current->signal->oom_score_adj); - cpuset_print_task_mems_allowed(current); - task_unlock(current); + cpuset_print_current_mems_allowed(); dump_stack(); if (memcg) mem_cgroup_print_oom_info(memcg, p); @@ -509,10 +507,8 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, if (__ratelimit(&oom_rs)) dump_header(oc, p, memcg); - task_lock(p); pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n", message, task_pid_nr(p), p->comm, points); - task_unlock(p); /* * If any of p's children has a different mm and is eligible for kill, @@ -586,10 +582,8 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p, if (fatal_signal_pending(p)) continue; - task_lock(p); /* Protect ->comm from prctl() */ pr_info("Kill process %d (%s) sharing same memory\n", task_pid_nr(p), p->comm); - task_unlock(p); do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true); } rcu_read_unlock(); -- cgit