The patch titled Subject: mm: fix kthread_use_mm() vs TLB invalidate has been added to the -mm tree. Its filename is mm-fix-kthread_use_mm-vs-tlb-invalidate.patch

This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-fix-kthread_use_mm-vs-tlb-invali... and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-fix-kthread_use_mm-vs-tlb-invali...

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------------------------------------------------------ From: Peter Zijlstra peterz@infradead.org Subject: mm: fix kthread_use_mm() vs TLB invalidate

For SMP systems using IPI based TLB invalidation, looking at current->active_mm is entirely reasonable. This then presents the following race condition:

CPU0 CPU1

flush_tlb_mm(mm) use_mm(mm) <send-IPI> tsk->active_mm = mm; <IPI> if (tsk->active_mm == mm) // flush TLBs </IPI> switch_mm(old_mm,mm,tsk);

Where it is possible the IPI flushed the TLBs for @old_mm, not @mm, because the IPI lands before we actually switched.

Avoid this by disabling IRQs across changing ->active_mm and switch_mm().

[ There are all sorts of reasons this might be harmless for various architecture specific reasons, but best not leave the door open at all. ]

Link: http://lkml.kernel.org/r/20200721154106.GE10769@hirez.programming.kicks-ass.... Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reported-by: Andy Lutomirski luto@amacapital.net Cc: Jens Axboe axboe@kernel.dk Cc: Kees Cook keescook@chromium.org Cc: Jann Horn jannh@google.com Cc: Will Deacon will@kernel.org Cc: Christoph Hellwig hch@lst.de Cc: Nicholas Piggin npiggin@gmail.com Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

kernel/kthread.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/kernel/kthread.c~mm-fix-kthread_use_mm-vs-tlb-invalidate +++ a/kernel/kthread.c @@ -1239,13 +1239,15 @@ void kthread_use_mm(struct mm_struct *mm WARN_ON_ONCE(tsk->mm);

task_lock(tsk); + local_irq_disable(); active_mm = tsk->active_mm; if (active_mm != mm) { mmgrab(mm); tsk->active_mm = mm; } tsk->mm = mm; - switch_mm(active_mm, mm, tsk); + switch_mm_irqs_off(active_mm, mm, tsk); + local_irq_enable(); task_unlock(tsk); #ifdef finish_arch_post_lock_switch finish_arch_post_lock_switch(); @@ -1274,9 +1276,11 @@ void kthread_unuse_mm(struct mm_struct *

task_lock(tsk); sync_mm_rss(mm); + local_irq_disable(); tsk->mm = NULL; /* active_mm is still 'mm' */ enter_lazy_tlb(mm, tsk); + local_irq_enable(); task_unlock(tsk); } EXPORT_SYMBOL_GPL(kthread_unuse_mm); _

Patches currently in -mm which might be from peterz@infradead.org are

mm-fix-kthread_use_mm-vs-tlb-invalidate.patch