linux-kernel - Re: [PATCH -fixes] riscv: uaccess: Return the number of bytes effectively copied

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Message-ID: <87r0o9ahce.fsf@all.your.base.are.belong.to.us>
Date:   Fri, 11 Aug 2023 14:33:53 +0200
From:   Björn Töpel <bjorn@...nel.org>
To:     Alexandre Ghiti <alex@...ti.fr>,
        Alexandre Ghiti <alexghiti@...osinc.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alan Kao <alankao@...estech.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Bo YU <tsu.yubo@...il.com>, Aurelien Jarno <aurelien@...el32.net>
Subject: Re: [PATCH -fixes] riscv: uaccess: Return the number of bytes
 effectively copied

Alexandre Ghiti <alex@...ti.fr> writes:

> On 11/08/2023 13:03, Alexandre Ghiti wrote:
>> It was reported that the riscv kernel hangs while executing the test
>> in [1].
>>
>> Indeed, the test hangs when trying to write a buffer to a file. The
>> problem is that the riscv implementation of raw_copy_from_user() does not
>> return the number of bytes written when an exception happens and is fixed
>> up.
>
>
> I'll respin another version as the changelog and the title are 
> incorrect: the uaccess routines should not return the number of bytes 
> copied but actually the number of bytes not copied (this is what this 
> patch implements).
>
> I'll wait for feedbacks before doing so!

Yikes! Nice catch.

Functions like fault_in_readable() will fail horribly w/o this. I wonder
why we haven't seen this problem more?

Feel free to add my RB to your next spin!

Reviewed-by: Björn Töpel <bjorn@...osinc.com>