| From | Greg Kroah-Hartman <> | Subject | [PATCH 5.4 081/214] mm: fix kthread_use_mm() vs TLB invalidate | Date | Tue, 1 Sep 2020 17:09:21 +0200 |
| |
From: Peter Zijlstra <peterz@infradead.org>
[ Upstream commit 38cf307c1f2011d413750c5acb725456f47d9172 ]
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().
Of the (SMP) architectures that have IPI based TLB invalidate:
Alpha - checks active_mm ARC - ASID specific IA64 - checks active_mm MIPS - ASID specific flush OpenRISC - shoots down world PARISC - shoots down world SH - ASID specific SPARC - ASID specific x86 - N/A xtensa - checks active_mm
So at the very least Alpha, IA64 and Xtensa are suspect.
On top of this, for scheduler consistency we need at least preemption disabled across changing tsk->mm and doing switch_mm(), which is currently provided by task_lock(), but that's not sufficient for PREEMPT_RT.
[akpm@linux-foundation.org: add comment]
Reported-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Nicholas Piggin <npiggin@gmail.com> 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: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200721154106.GE10769@hirez.programming.kicks-ass.net Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> --- mm/mmu_context.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/mm/mmu_context.c b/mm/mmu_context.c index 3e612ae748e96..a1da47e027479 100644 --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -25,13 +25,16 @@ void use_mm(struct mm_struct *mm) struct task_struct *tsk = current; task_lock(tsk); + /* Hold off tlb flush IPIs while switching mm's */ + 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(); @@ -56,9 +59,11 @@ void unuse_mm(struct mm_struct *mm) 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(unuse_mm); -- 2.25.1
|