linux-kernel - Re: [PATCH v2 7/8] mm/memory_hotplug: Make unregister_memory_block_under

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Message-ID: <CAPcyv4jtS6G_ZqLCdO4gOjS9K2cuX=ywFHemhSb46aQvS8pa8A@mail.gmail.com>
Date:   Wed, 8 May 2019 06:50:25 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-ia64@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Linux-sh <linux-sh@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Alex Deucher <alexander.deucher@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Mark Brown <broonie@...nel.org>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Oscar Salvador <osalvador@...e.de>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v2 7/8] mm/memory_hotplug: Make unregister_memory_block_under_nodes()
 never fail

On Wed, May 8, 2019 at 12:22 AM David Hildenbrand <david@...hat.com> wrote:
>
>
> >>  drivers/base/node.c  | 18 +++++-------------
> >>  include/linux/node.h |  5 ++---
> >>  2 files changed, 7 insertions(+), 16 deletions(-)
> >>
> >> diff --git a/drivers/base/node.c b/drivers/base/node.c
> >> index 04fdfa99b8bc..9be88fd05147 100644
> >> --- a/drivers/base/node.c
> >> +++ b/drivers/base/node.c
> >> @@ -803,20 +803,14 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg)
> >>
> >>  /*
> >>   * Unregister memory block device under all nodes that it spans.
> >> + * Has to be called with mem_sysfs_mutex held (due to unlinked_nodes).
> >
> > Given this comment can bitrot relative to the implementation lets
> > instead add an explicit:
> >
> >     lockdep_assert_held(&mem_sysfs_mutex);
>
> That would require to make the mutex non-static. Is that what you
> suggest, or any other alternative?

If the concern is other code paths taking the lock when they shouldn't
then you could make a public "lockdep_assert_mem_sysfs_held()" to do
the same, but I otherwise think the benefit of inline lock validation
is worth the price of adding a new non-static symbol.