Re: [PATCH] mm,shmem: Fix a typo in shmem_swapin_page()

[Matthew Wilcox]

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@xxxxxxxxx>
> 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@xxxxxxxxx
> Fixes: 2efa33fc7f6e ("mm/shmem: fix shmem_swapin() race with swapoff")
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>

Suggested-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>

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.