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authorPeter Zijlstra <peterz@infradead.org>2020-08-06 23:17:16 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-07 11:33:21 -0700
commit38cf307c1f2011d413750c5acb725456f47d9172 (patch)
treec6f5931300d455adb1f2e87e6a6651d562d1c4c4
parent4a93025cbe4a0b19d1a25a2d763a3d2018bad0d9 (diff)
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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(). 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>
-rw-r--r--kernel/kthread.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 1d9e2fdfd67a..1c8964feeb01 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1241,13 +1241,16 @@ void kthread_use_mm(struct mm_struct *mm)
WARN_ON_ONCE(tsk->mm);
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();
@@ -1276,9 +1279,11 @@ void kthread_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(kthread_unuse_mm);