linux-kernel - Re: [PATCH] mm/vmalloc: Check absolute error return from vmap_[p4d|pud|pmd|pte]

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Date:   Fri, 14 Jun 2019 10:57:42 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Roman Penyaev <rpenyaev@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...e.com>,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm/vmalloc: Check absolute error return from
 vmap_[p4d|pud|pmd|pte]_range()



On 06/13/2019 09:01 PM, Matthew Wilcox wrote:
> On Thu, Jun 13, 2019 at 08:51:17PM +0530, Anshuman Khandual wrote:
>> acceptable ? What we have currently is wrong where vmap_pmd_range() could
>> just wrap EBUSY as ENOMEM and send up the call chain.
> 
> It's not wrong.  We do it in lots of places.  Unless there's a caller
> which really needs to know the difference, it's often better than
> returning the "real error".

I can understand the fact that because there are no active users of this
return code, the current situation has been alright. But then I fail to
understand how can EBUSY be made ENOMEM and let the caller to think that
vmap_page_rage() failed because of lack of memory when it is clearly not
the case. It is really surprising how it can be acceptable inside kernel
(init_mm) page table functions which need to be thorough enough.