linux-kernel - Re: [PATCH v6 1/1] xen/time: do not decrease steal time after live migration on xen

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Date:   Thu, 2 Nov 2017 16:28:31 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     jgross@...e.com, joao.m.martins@...cle.com
Subject: Re: [PATCH v6 1/1] xen/time: do not decrease steal time after live
 migration on xen

On 11/01/2017 09:19 PM, Dongli Zhang wrote:
> Hi Boris,
>
> I have received from lkp@...el.com that the prior version of patch hit issue
> during compilation with aarch64-linux-gnu-gcc. I think this patch reviewed by
> you would hit the same compiling issue on arm64 (there is no issue with x86_64).
>
> -------------------------------------------------------------
>
> 1st issue:
>
> Without including header <linux/slab.h> into driver/xen/time.c, compilation on
> x86_64 works well (without any warning or error) but arm64 would hit the
> following error:
>
> drivers/xen/time.c: In function ‘xen_manage_runstate_time’:
> drivers/xen/time.c:94:20: error: implicit declaration of function
> ‘kmalloc_array’ [-Werror=implicit-function-declaration]
>    runstate_delta = kmalloc_array(num_possible_cpus(),
>                     ^
>
> drivers/xen/time.c:131:3: error: implicit declaration of function ‘kfree’
> [-Werror=implicit-function-declaration]
>    kfree(runstate_delta);
>    ^
> cc1: some warnings being treated as errors
>
> About the 1st issue, should I submit a new patch including <linux/slab.h> or
> just a incremental based on previous patch merged into your own branch
> /tree?
>
> -------------------------------------------------------------
>
> 2nd issue:
>
> aarch64-linux-gnu-gcc expects a cast for kmalloc_array(). Is this really
> necessary as I did find people casting the return type of
> kmalloc/kcalloc/kmalloc_array in linux source code (e.g.,
> drivers/block/virtio_blk.c). Can we just ignore this warning?
>
> drivers/xen/time.c:94:18: warning: assignment makes pointer from integer without
> a cast [-Wint-conversion]
>    runstate_delta = kmalloc_array(num_possible_cpus(),
>                   ^
> -------------------------------------------------------------

That's because you need to declare kmalloc_array(), otherwise the
compiler by default assumes that it returns an int. So including
linux/slab.h should take care of both warnings.

I can add it while committing.


-boris