On Wed 03-12-14 20:50:20, Oleg Nesterov wrote: > oom_kill.c assumes that PF_EXITING task should exit and free the memory > soon. This is wrong in many ways and one important case is the coredump. > A task can sleep in exit_mm() "forever" while the coredumping sub-thread > can need more memory. > > Change the PF_EXITING checks to take SIGNAL_GROUP_COREDUMP into account, > we add the new trivial helper for that. > > Note: this is only the first step, this patch doesn't try to solve other > problems. The SIGNAL_GROUP_COREDUMP check is obviously racy, a task can > participate in coredump after it was already observed in PF_EXITING state, > so TIF_MEMDIE (which also blocks oom-killer) still can be wrongly set. > fatal_signal_pending() can be true because of SIGNAL_GROUP_COREDUMP so > out_of_memory() and mem_cgroup_out_of_memory() shouldn't blindly trust it. > And even the name/usage of the new helper is confusing, an exiting thread > can only free its ->mm if it is the only/last task in thread group. > > Signed-off-by: Oleg Nesterov <[email protected]>
OK, I do not have a better name for the helper and code duplication looks even worse so Acked-by: Michal Hocko <[email protected]> Andrew's additional comment makes sense as well. > --- > include/linux/oom.h | 6 ++++++ > mm/memcontrol.c | 2 +- > mm/oom_kill.c | 6 +++--- > 3 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/include/linux/oom.h b/include/linux/oom.h > index e8d6e10..e16b945 100644 > --- a/include/linux/oom.h > +++ b/include/linux/oom.h > @@ -92,6 +92,12 @@ static inline bool oom_gfp_allowed(gfp_t gfp_mask) > > extern struct task_struct *find_lock_task_mm(struct task_struct *p); > > +static inline bool task_will_free_mem(struct task_struct *task) > +{ > + return (task->flags & PF_EXITING) && > + !(task->signal->flags & SIGNAL_GROUP_COREDUMP); > +} > + > /* sysctls */ > extern int sysctl_oom_dump_tasks; > extern int sysctl_oom_kill_allocating_task; > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index d6ac0e3..3d1d49f 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1734,7 +1734,7 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup > *memcg, gfp_t gfp_mask, > * select it. The goal is to allow it to allocate so that it may > * quickly exit and free its memory. > */ > - if (fatal_signal_pending(current) || current->flags & PF_EXITING) { > + if (fatal_signal_pending(current) || task_will_free_mem(current)) { > set_thread_flag(TIF_MEMDIE); > return; > } > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 5340f6b..837ff31 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -281,7 +281,7 @@ enum oom_scan_t oom_scan_process_thread(struct > task_struct *task, > if (oom_task_origin(task)) > return OOM_SCAN_SELECT; > > - if (task->flags & PF_EXITING && !force_kill) { > + if (task_will_free_mem(task) && !force_kill) { > /* > * If this task is not being ptraced on exit, then wait for it > * to finish before killing some other task unnecessarily. > @@ -443,7 +443,7 @@ void oom_kill_process(struct task_struct *p, gfp_t > gfp_mask, int order, > * If the task is already exiting, don't alarm the sysadmin or kill > * its children or threads, just set TIF_MEMDIE so it can die quickly > */ > - if (p->flags & PF_EXITING) { > + if (task_will_free_mem(p)) { > set_tsk_thread_flag(p, TIF_MEMDIE); > put_task_struct(p); > return; > @@ -649,7 +649,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t > gfp_mask, > * select it. The goal is to allow it to allocate so that it may > * quickly exit and free its memory. > */ > - if (fatal_signal_pending(current) || current->flags & PF_EXITING) { > + if (fatal_signal_pending(current) || task_will_free_mem(current)) { > set_thread_flag(TIF_MEMDIE); > return; > } > -- > 1.5.5.1 > > -- 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/
