linux-kernel - Re: [PATCH] RISC-V: Fix error code returned by riscv_hartid_to

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Date:   Fri, 23 Apr 2021 00:15:55 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     Anup Patel <Anup.Patel@....com>
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        Atish Patra <Atish.Patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        anup@...infault.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Anup Patel <Anup.Patel@....com>,
        stable@...r.kernel.org
Subject:     Re: [PATCH] RISC-V: Fix error code returned by riscv_hartid_to_cpuid()

On Thu, 15 Apr 2021 01:55:22 PDT (-0700), Anup Patel wrote:
> We should return a negative error code upon failure in

Not just should: the PLIC driver assumed this was the return flavor and 
will overflow a per_cpu because it doesn't detect the error.  IIUC this 
will manifest if we have more harts that NR_CPUS, which is a possible 
configuration.

That said, it's gone unnoticed for ~3 years so I'm inclined to leave it 
out of fixes because I have nothing else and this late in the cycle is 
always a bit touchy.  It's kind of splitting hairs as it'll just get 
backported, but post-rc8 is an odd spot to be in.

Is this actually manifesting as a crash for you?

Sorry I missed this last week.

> riscv_hartid_to_cpuid() instead of NR_CPUS. This is also
> aligned with all uses of riscv_hartid_to_cpuid() which
> expect negative error code upon failure.
>
> Fixes: 6825c7a80f18 ("RISC-V: Add logical CPU indexing for RISC-V")

Also

Fixes: f99fb607fb2b ("RISC-V: Use Linux logical CPU number instead of hartid")

which is what actually manifests the bug -- again, kind of splitting 
hairs as it's the patch after.

> Cc: stable@...r.kernel.org
> Signed-off-by: Anup Patel <anup.patel@....com>
> ---
>  arch/riscv/kernel/smp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c
> index ea028d9e0d24..d44567490d91 100644
> --- a/arch/riscv/kernel/smp.c
> +++ b/arch/riscv/kernel/smp.c
> @@ -54,7 +54,7 @@ int riscv_hartid_to_cpuid(int hartid)
>  			return i;
>
>  	pr_err("Couldn't find cpu id for hartid [%d]\n", hartid);
> -	return i;
> +	return -ENOENT;
>  }
>
>  void riscv_cpuid_to_hartid_mask(const struct cpumask *in, struct cpumask *out)