linux-kernel - Re: [PATCH v1 2/6] mm/page_isolation: don't dump_page(NULL) in set_migratetype

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Message-ID: <CAM9Jb+gGhg9umBKZRbkCDAAgqi+4VqMzN0BZ5v0hVPoR7gdhvA@mail.gmail.com>
Date:   Thu, 30 Jul 2020 06:21:33 +0200
From:   Pankaj Gupta <pankaj.gupta.linux@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Michael S . Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v1 2/6] mm/page_isolation: don't dump_page(NULL) in set_migratetype_isolate()

> Right now, if we have two isolations racing, we might trigger the
> WARN_ON_ONCE() and to dump_page(NULL), dereferencing NULL. Let's just
> return directly.
>
> In the future, we might want to report -EAGAIN to the caller instead, as
> this could indicate a temporary isolation failure only.
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  mm/page_isolation.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index f6d07c5f0d34d..553b49a34cf71 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -29,10 +29,12 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
>         /*
>          * We assume the caller intended to SET migrate type to isolate.
>          * If it is already set, then someone else must have raced and
> -        * set it before us.  Return -EBUSY
> +        * set it before us.
>          */
> -       if (is_migrate_isolate_page(page))
> -               goto out;
> +       if (is_migrate_isolate_page(page)) {
> +               spin_unlock_irqrestore(&zone->lock, flags);
> +               return -EBUSY;
> +       }
>
>         /*
>          * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
> --

Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@...il.com>

> 2.26.2
>
>