On Tue 22-09-15 16:30:13, David Rientjes wrote: > 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.
cpuset_print_task_mems_allowed seems unrelated and it would probably deserve a separate pach. > Suggested-by: Oleg Nesterov <[email protected]> > Signed-off-by: David Rientjes <[email protected]> For the task_lock part Acked-by: Michal Hocko <[email protected]> > --- > 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 > --- 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 > --- a/kernel/cpuset.c > +++ b/kernel/cpuset.c > @@ -2599,22 +2599,22 @@ 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 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -386,13 +386,11 @@ 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); > @@ -518,10 +516,8 @@ 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 (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) > continue; > > - task_lock(p); /* Protect ->comm from prctl() */ > pr_err("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(); -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
