[PATCH] mm: multi-gen LRU: Move lru_gen_add_mm() out of IRQ-off region.

[PATCH] mm: multi-gen LRU: Move lru_gen_add_mm() out of IRQ-off region.

[Sebastian Andrzej Siewior]

lru_gen_add_mm() has been added within an IRQ-off region in the commit
mentioned below. The other invocations of lru_gen_add_mm() are not within
an IRQ-off region.
The invocation within IRQ-off region is problematic on PREEMPT_RT
because the function is using a spin_lock_t which must not be used
within IRQ-disabled regions.

The other invocations of lru_gen_add_mm() occur while task_struct::alloc_lock
is acquired.
Move lru_gen_add_mm() after interrupts are enabled and before
task_unlock().

Fixes: bd74fdaea1460 ("mm: multi-gen LRU: support page table walks")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 fs/exec.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1012,7 +1012,6 @@ static int exec_mmap(struct mm_struct *m
 	active_mm = tsk->active_mm;
 	tsk->active_mm = mm;
 	tsk->mm = mm;
-	lru_gen_add_mm(mm);
 	/*
 	 * This prevents preemption while active_mm is being loaded and
 	 * it and mm are being updated, which could cause problems for
@@ -1025,6 +1024,7 @@ static int exec_mmap(struct mm_struct *m
 	activate_mm(active_mm, mm);
 	if (IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM))
 		local_irq_enable();
+	lru_gen_add_mm(mm);
 	task_unlock(tsk);
 	lru_gen_use_mm(mm);
 	if (old_mm) {

Re: [PATCH] mm: multi-gen LRU: Move lru_gen_add_mm() out of IRQ-off region.

[Yu Zhao]

On Wed, Oct 26, 2022 at 7:49 AM Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
>
> lru_gen_add_mm() has been added within an IRQ-off region in the commit
> mentioned below. The other invocations of lru_gen_add_mm() are not within
> an IRQ-off region.
> The invocation within IRQ-off region is problematic on PREEMPT_RT
> because the function is using a spin_lock_t which must not be used
> within IRQ-disabled regions.
>
> The other invocations of lru_gen_add_mm() occur while task_struct::alloc_lock
> is acquired.
> Move lru_gen_add_mm() after interrupts are enabled and before
> task_unlock().
>
> Fixes: bd74fdaea1460 ("mm: multi-gen LRU: support page table walks")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Thanks.

Acked-by: Yu Zhao <yuzhao@google.com>