linux-kernel - Re: [PATCH] mm,shmem: Fix a typo in shmem_swapin

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Date:   Tue, 3 Aug 2021 12:59:10 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Yang Shi <shy828301@...il.com>, Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Minchan Kim <minchan@...nel.org>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH] mm,shmem: Fix a typo in shmem_swapin_page()

On Tue, Aug 03, 2021 at 04:06:47PM +0800, Huang, Ying wrote:
> As Hugh pointed out, EINVAL isn't an appropriate error code for race
> condition.  After checking the code, I found that EEXIST is the error
> code used for race condition.  So I revise the patch as below.  If Hugh
> doesn't object, can you help to replace the patch with the below one?
> 
> Best Regards,
> Huang, Ying
> 
> -----------------------------8<---------------------------------------
> >From e2b281a0b09d34d6463942e214e577ed9357c213 Mon Sep 17 00:00:00 2001
> From: Huang Ying <ying.huang@...el.com>
> Date: Tue, 3 Aug 2021 10:51:16 +0800
> Subject: [PATCH] shmem_swapin_page(): fix error processing for
>  get_swap_device()
> 
> Firstly, "-" is missing before the error code.  Secondly, EINVAL isn't
> the proper error code for the race condition.  EEXIST is used in
> shmem_swapin_page() for that.  So the error code is changed to EEXIST
> too.
> 
> Link: https://lkml.kernel.org/r/20210723080000.93953-1-ying.huang@intel.com
> Fixes: 2efa33fc7f6e ("mm/shmem: fix shmem_swapin() race with swapoff")
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>

Suggested-by: Matthew Wilcox (Oracle) <willy@...radead.org>

Also, the description is poor.  How about:

If we hit this rare race, returning EINVAL (or even -EINVAL) would cause
the page fault to be handled as a SIGBUS.  This is not correct; the page
is not missing or unreadable, it has simply changed location.  Returning
-EEXIST here will cause the lookup to be retried by the caller.