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From: Michel Lespinasse <walken@google.com>
To: Jann Horn <jannh@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Jeff Dike <jdike@addtoit.com>,
	Richard Weinberger <richard@nod.at>,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	linux-um@lists.infradead.org, Jason Gunthorpe <jgg@nvidia.com>,
	John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH 1/2] mmap locking API: Order lock of nascent mm outside lock of live mm
Date: Fri, 2 Oct 2020 02:17:49 -0700	[thread overview]
Message-ID: <CANN689H9hXzaV0_vpFfrvjQD6xAEaPnjok_17zWGHumRNs-ZWg@mail.gmail.com> (raw)
In-Reply-To: <CAG48ez1kMuPUW8VKp=9=KDLVisa-zuqp+DbYjc=A-kGUi_ik3A@mail.gmail.com>

On Thu, Oct 1, 2020 at 6:25 PM Jann Horn <jannh@google.com> wrote:
> Until now, the mmap lock of the nascent mm was ordered inside the mmap lock
> of the old mm (in dup_mmap() and in UML's activate_mm()).
> A following patch will change the exec path to very broadly lock the
> nascent mm, but fine-grained locking should still work at the same time for
> the new mm.
> To do this in a way that lockdep is happy about, let's turn around the lock
> ordering in both places that currently nest the locks.
> Since SINGLE_DEPTH_NESTING is normally used for the inner nesting layer,
> make up our own lock subclass MMAP_LOCK_SUBCLASS_NASCENT and use that
> instead.
>
> The added locking calls in exec_mmap() are temporary; the following patch
> will move the locking out of exec_mmap().

Thanks for doing this.

This is probably a silly question, but I am not sure exactly where we
lock the old MM while bprm is creating the new MM ? I am guessing this
would be only in setup_arg_pages(), copying the args and environment
from the old the the new MM ? If that is correct, then wouldn't it be
sufficient to use mmap_write_lock_nested in setup_arg_pages() ? Or, is
the issue that we'd prefer to have a killable version of it there ?

Also FYI I was going to play with these patches a bit to help answer
these questions on my own, but wasn't able to easily apply them as
they came lightly mangled (whitespace issues) when I saved them.

  reply	other threads:[~2020-10-02  9:18 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-02  1:23 [PATCH 0/2] Broad write-locking of nascent mm in execve Jann Horn
2020-10-02  1:24 ` [PATCH 1/2] mmap locking API: Order lock of nascent mm outside lock of live mm Jann Horn
2020-10-02  9:17   ` Michel Lespinasse [this message]
2020-10-02 11:39     ` Jason Gunthorpe
2020-10-02 16:33     ` Jann Horn
2020-10-03 21:30       ` Michel Lespinasse
2020-10-05  1:30         ` Jann Horn
2020-10-05 12:52           ` Jason Gunthorpe
2020-10-02  1:25 ` [PATCH 2/2] exec: Broadly lock nascent mm until setup_arg_pages() Jann Horn

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