linux-kernel - Re: [PATCH 2/3] mm, notifier: Catch sleeping/blocking for !blockable

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Date:   Fri, 23 Nov 2018 12:12:37 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     LKML <linux-kernel@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Christian König <christian.koenig@....com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 2/3] mm, notifier: Catch sleeping/blocking for !blockable

On Thu 22-11-18 17:51:05, Daniel Vetter wrote:
> We need to make sure implementations don't cheat and don't have a
> possible schedule/blocking point deeply burried where review can't
> catch it.
> 
> I'm not sure whether this is the best way to make sure all the
> might_sleep() callsites trigger, and it's a bit ugly in the code flow.
> But it gets the job done.

Yeah, it is quite ugly. Especially because it makes DEBUG config
bahavior much different. So is this really worth it? Has this already
discovered any existing bug?

> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: "Christian König" <christian.koenig@....com>
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> Cc: "Jérôme Glisse" <jglisse@...hat.com>
> Cc: linux-mm@...ck.org
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
> ---
>  mm/mmu_notifier.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
> index 59e102589a25..4d282cfb296e 100644
> --- a/mm/mmu_notifier.c
> +++ b/mm/mmu_notifier.c
> @@ -185,7 +185,13 @@ int __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
>  	id = srcu_read_lock(&srcu);
>  	hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) {
>  		if (mn->ops->invalidate_range_start) {
> -			int _ret = mn->ops->invalidate_range_start(mn, mm, start, end, blockable);
> +			int _ret;
> +
> +			if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_SLEEP) && !blockable)
> +				preempt_disable();
> +			_ret = mn->ops->invalidate_range_start(mn, mm, start, end, blockable);
> +			if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_SLEEP) && !blockable)
> +				preempt_enable();
>  			if (_ret) {
>  				pr_info("%pS callback failed with %d in %sblockable context.\n",
>  						mn->ops->invalidate_range_start, _ret,
> -- 
> 2.19.1
> 

-- 
Michal Hocko
SUSE Labs