Commit da39da3a authored by David Rientjes's avatar David Rientjes Committed by Linus Torvalds
Browse files

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: default avatarDavid Rientjes <rientjes@google.com>
Suggested-by: default avatarOleg 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: default avatarJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2d1e1041

include/linux/cpuset.h

+2 −2
Original line number Diff line number Diff line
@@ -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)

{

}

kernel/cpuset.c

+7 −7
Original line number Diff line number Diff line
@@ -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();

}

mm/oom_kill.c

+1 −7
Original line number Diff line number Diff line
@@ -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();

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