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 <rientjes@google.com>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 1b35799..5a13119 100644 (file)
--- 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 f0acff0..9ef59a3 100644 (file)
--- 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(&current->mems_allowed));
 
        rcu_read_unlock();
 }

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index c170d9f..58f3d27 100644 (file)
--- 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();