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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Jann Horn <jannh@google.com>
Cc: Michel Lespinasse <walken@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux-MM <linux-mm@kvack.org>,
	kernel list <linux-kernel@vger.kernel.org>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>
Subject: Re: [PATCH 3/4] mmap locking API: Don't check locking if the mm isn't live yet
Date: Thu, 1 Oct 2020 20:41:27 -0300	[thread overview]
Message-ID: <20201001234127.GG9916@ziepe.ca> (raw)
In-Reply-To: <CAG48ez3GW9sRfZWwx+YpKdouAVT+o9zQR73-itJMbLCXTiUxBw@mail.gmail.com>

On Thu, Oct 01, 2020 at 10:16:35PM +0200, Jann Horn wrote:

> > A subclass isn't right, it has to be a _nested annotation.
> >
> > nested locking is a pretty good reason to not be able to do this, this
> > is something lockdep does struggle to model.
> 
> Did I get the terminology wrong? I thought they were the same. The
> down_*_nested() APIs take an argument "subclass", with the default
> subclass for the functions without "_nested" being 0.

AFAIK a subclass at init time sticks with the lock forever, the
_nested ones are temporary overrides.

I think what you kind of want is to start out with
lockdep_set_novalidate_class() then switch to a real class once things
are finished. Not sure exactly how :)

Jason


  reply	other threads:[~2020-10-01 23:41 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20200930011944.19869-1-jannh@google.com>
2020-09-30  1:20 ` [PATCH 2/4] binfmt_elf: Take the mmap lock around find_extend_vma() Jann Horn
2020-09-30 23:22   ` Michel Lespinasse
2020-09-30  1:20 ` [PATCH 3/4] mmap locking API: Don't check locking if the mm isn't live yet Jann Horn
2020-09-30 12:30   ` Jason Gunthorpe
2020-09-30 12:50     ` Jann Horn
2020-09-30 20:14       ` Jann Horn
2020-09-30 23:26         ` Jason Gunthorpe
2020-09-30 23:51           ` Jann Horn
2020-10-01 19:15             ` Jason Gunthorpe
2020-10-01 20:16               ` Jann Horn
2020-10-01 23:41                 ` Jason Gunthorpe [this message]
2020-10-01 23:55                   ` Jann Horn
2020-09-30 23:42         ` Michel Lespinasse
2020-09-30  1:20 ` [PATCH 4/4] mm/gup: Assert that the mmap lock is held in __get_user_pages() Jann Horn
2020-09-30 12:32   ` Jason Gunthorpe
2020-09-30 23:24     ` Michel Lespinasse

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