lib/kunit/user_alloc.c currently uses kthread_use_mm() without a corresponding kthread_unuse_mm(). This is a bug, but fixing it in KUnit makes writing tests that use mms more difficult, because of KUnit's resource/try-catch model.
Therefore, introduce a new operation that does what kunit_attach_mm() wants, namely an unbalanced call with cleanup deferred to kthread_exit(). This is actually just the same as kthread_use_mm() but without taking a reference on the mm_struct. While adding this, clarify the reference returned by mm_alloc(), since that is what kthread_take_mm() is gonna be paired with, in practice. Signed-off-by: Brendan Jackman <[email protected]> --- include/linux/kthread.h | 1 + kernel/fork.c | 3 ++- kernel/kthread.c | 36 +++++++++++++++++++++++++++--------- 3 files changed, 30 insertions(+), 10 deletions(-) diff --git a/include/linux/kthread.h b/include/linux/kthread.h index 8d27403888ce9..2e6244d8ff1a3 100644 --- a/include/linux/kthread.h +++ b/include/linux/kthread.h @@ -259,6 +259,7 @@ bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *work); void kthread_destroy_worker(struct kthread_worker *worker); +void kthread_take_mm(struct mm_struct *mm); void kthread_use_mm(struct mm_struct *mm); void kthread_unuse_mm(struct mm_struct *mm); diff --git a/kernel/fork.c b/kernel/fork.c index b1f3915d5f8ec..761e6232ea75a 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1147,7 +1147,8 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, } /* - * Allocate and initialize an mm_struct. + * Allocate and initialize an mm_struct. The caller gets a single reference to + * the mm's address space, which should be released with a call to mmput(). */ struct mm_struct *mm_alloc(void) { diff --git a/kernel/kthread.c b/kernel/kthread.c index 99a3808d086f0..c660c04a1b627 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -1589,10 +1589,16 @@ void kthread_destroy_worker(struct kthread_worker *worker) EXPORT_SYMBOL(kthread_destroy_worker); /** - * kthread_use_mm - make the calling kthread operate on an address space + * kthread_take_mm - make the calling kthread own an address space. + * + * Unlike kthread_use_mm(), this doesn't have a cleanup, instead that happens + * automatically on kthread exit. Correspondingly, it does not take any + * references, by calling this function you donate your reference to the address + * space (from mmget()/mm_users). + * * @mm: address space to operate on */ -void kthread_use_mm(struct mm_struct *mm) +void kthread_take_mm(struct mm_struct *mm) { struct mm_struct *active_mm; struct task_struct *tsk = current; @@ -1600,13 +1606,6 @@ void kthread_use_mm(struct mm_struct *mm) WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD)); WARN_ON_ONCE(tsk->mm); - /* - * It is possible for mm to be the same as tsk->active_mm, but - * we must still mmgrab(mm) and mmdrop_lazy_tlb(active_mm), - * because these references are not equivalent. - */ - mmgrab(mm); - task_lock(tsk); /* Hold off tlb flush IPIs while switching mm's */ local_irq_disable(); @@ -1632,6 +1631,25 @@ void kthread_use_mm(struct mm_struct *mm) */ mmdrop_lazy_tlb(active_mm); } +EXPORT_SYMBOL_GPL(kthread_take_mm); + +/** + * kthread_use_mm - make the calling kthread operate on an address space. + * + * This must be paired with a call to kthread_unuse_mm(). + * + * @mm: address space to operate on + */ +void kthread_use_mm(struct mm_struct *mm) +{ + /* + * It is possible for mm to be the same as tsk->active_mm, but we must + * still mmgrab(mm) and mmdrop_lazy_tlb(active_mm) (in + * kthread_take_mm()), because these references are not equivalent. + */ + mmgrab(mm); + kthread_take_mm(mm); +} EXPORT_SYMBOL_GPL(kthread_use_mm); /** -- 2.51.2
