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

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Date:   Thu, 13 Jun 2019 11:33:02 +0200
From:   Roman Penyaev <rpenyaev@...e.de>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     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 2019-06-13 10:12, Anshuman Khandual wrote:
> vmap_pte_range() returns an -EBUSY when it encounters a non-empty PTE. 
> But
> currently vmap_pmd_range() unifies both -EBUSY and -ENOMEM return code 
> as
> -ENOMEM and send it up the call chain which is wrong. Interestingly 
> enough
> vmap_page_range_noflush() tests for the absolute error return value 
> from
> vmap_p4d_range() but it does not help because -EBUSY has been merged 
> with
> -ENOMEM. So all it can return is -ENOMEM. Fix this by testing for 
> absolute
> error return from vmap_pmd_range() all the way up to vmap_p4d_range().

I could not find any real external caller of vmap API who really cares
about the errno, and frankly why they should?  This is allocation path,
allocation failed - game over.  When you step on -EBUSY case something
has gone completely wrong in your kernel, you get a big warning in
your dmesg and it is already does not matter what errno you get.

--
Roman