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From: Andrew Morton <akpm@linux-foundation.org>
To: Luigi Rizzo <lrizzo@google.com>
Cc: linux-kernel@vger.kernel.org,
	David Rientjes <rientjes@google.com>,
	linux-mm@kvack.org
Subject: Re: [PATCH] Add mmap_assert_locked() annotations to find_vma*()
Date: Sun, 1 Aug 2021 12:33:35 -0700	[thread overview]
Message-ID: <20210801123335.6a7f8e1ee1e52ea64db80323@linux-foundation.org> (raw)
In-Reply-To: <20210731175341.3458608-1-lrizzo@google.com>

On Sat, 31 Jul 2021 10:53:41 -0700 Luigi Rizzo <lrizzo@google.com> wrote:

> find_vma() and variants need protection when used.
> This patch adds mmap_assert_lock() calls in the functions.
> 
> To make sure the invariant is satisfied, we also need to add a
> mmap_read_loc() around the get_user_pages_remote() call in
> get_arg_page(). The lock is not strictly necessary because the mm
> has been newly created, but the extra cost is limited because
> the same mutex was also acquired shortly before in __bprm_mm_init(),
> so it is hot and uncontended.
> 

Well, it isn't cost-free.  find_vma() is called a lot and a surprising
number of systems apparently run with CONFIG_DEBUG_VM.  Why do you
think this cost is justified?


  reply	other threads:[~2021-08-01 19:33 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-31 17:53 [PATCH] Add mmap_assert_locked() annotations to find_vma*() Luigi Rizzo
2021-08-01 19:33 ` Andrew Morton [this message]
2021-08-02  0:16   ` Luigi Rizzo
2021-08-02 21:11     ` Andrew Morton
2021-08-03 16:08 ` Jason Gunthorpe
2021-08-03 21:48   ` Luigi Rizzo
2021-08-03 23:07     ` Liam Howlett
2021-08-03 23:35       ` Jason Gunthorpe
2021-08-03 23:57         ` Luigi Rizzo
2021-08-04  5:12           ` Liam Howlett
2021-08-04 14:42       ` Jann Horn
2021-08-04 15:21         ` Jason Gunthorpe
2021-08-04 21:22           ` Jann Horn
2021-08-04 17:32         ` Liam Howlett

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