linux-kernel - Re: [PATCH RFC 3/3] mm/vmalloc.c: allow vread() to read out vm_map

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Message-ID: <Y3c77o95A9vKQ745@casper.infradead.org>
Date:   Fri, 18 Nov 2022 08:01:50 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, stephen.s.brennan@...cle.com,
        urezki@...il.com, hch@...radead.org
Subject: Re: [PATCH RFC 3/3] mm/vmalloc.c: allow vread() to read out
 vm_map_ram areas

On Wed, Nov 09, 2022 at 11:35:34AM +0800, Baoquan He wrote:
> Currently, vread() can read out vmalloc areas which is associated with
> a vm_struct. While this doesn't work for areas created by vm_map_ram()
> interface because it doesn't allocate a vm_struct. Then in vread(),
> these areas will be skipped.
> 
> Here, add a new function vb_vread() to read out areas managed by
> vmap_block specifically. Then recognize vm_map_ram areas via vmap->flags
> and handle  them respectively.

i don't understand how this deals with the original problem identified,
that the vread() can race with an unmap.