| Message ID | 20190726234541.3771-1-longman@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | sched/core: Don't use dying mm as active_mm for kernel threads | expand |
On 7/26/19 7:45 PM, Waiman Long wrote: > It was found that a dying mm_struct where the owning task has exited can > stay on as active_mm of kernel threads as long as no other user tasks > run on those CPUs that use it as active_mm. This prolongs the life time > of dying mm holding up memory and other resources that cannot be freed. > > Fix that by forcing the kernel threads to use init_mm as the active_mm > if the previous active_mm is dying. > > Signed-off-by: Waiman Long <longman@redhat.com> > --- > kernel/sched/core.c | 13 +++++++++++-- > mm/init-mm.c | 2 ++ > 2 files changed, 13 insertions(+), 2 deletions(-) Sorry, I didn't realize that mm->owner depends on CONFIG_MEMCG. I will need to refresh the patch and send out v2 when I am done testing. Cheers, Longman
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 2b037f195473..ca348e1f5a1e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3233,13 +3233,22 @@ context_switch(struct rq *rq, struct task_struct *prev, * Both of these contain the full memory barrier required by * membarrier after storing to rq->curr, before returning to * user-space. + * + * If mm is NULL and oldmm is dying (!owner), we switch to + * init_mm instead to make sure that oldmm can be freed ASAP. */ - if (!mm) { + if (!mm && oldmm->owner) { next->active_mm = oldmm; mmgrab(oldmm); enter_lazy_tlb(oldmm, next); - } else + } else { + if (!mm) { + mm = &init_mm; + next->active_mm = mm; + mmgrab(mm); + } switch_mm_irqs_off(oldmm, mm, next); + } if (!prev->mm) { prev->active_mm = NULL; diff --git a/mm/init-mm.c b/mm/init-mm.c index a787a319211e..5bfc6bc333ca 100644 --- a/mm/init-mm.c +++ b/mm/init-mm.c @@ -5,6 +5,7 @@ #include <linux/spinlock.h> #include <linux/list.h> #include <linux/cpumask.h> +#include <linux/sched/task.h> #include <linux/atomic.h> #include <linux/user_namespace.h> @@ -36,5 +37,6 @@ struct mm_struct init_mm = { .mmlist = LIST_HEAD_INIT(init_mm.mmlist), .user_ns = &init_user_ns, .cpu_bitmap = { [BITS_TO_LONGS(NR_CPUS)] = 0}, + .owner = &init_task, INIT_MM_CONTEXT(init_mm) };
It was found that a dying mm_struct where the owning task has exited can stay on as active_mm of kernel threads as long as no other user tasks run on those CPUs that use it as active_mm. This prolongs the life time of dying mm holding up memory and other resources that cannot be freed. Fix that by forcing the kernel threads to use init_mm as the active_mm if the previous active_mm is dying. Signed-off-by: Waiman Long <longman@redhat.com> --- kernel/sched/core.c | 13 +++++++++++-- mm/init-mm.c | 2 ++ 2 files changed, 13 insertions(+), 2 deletions(-)