linux-kernel - Re: [PATCH v2] of: Check for overlap in reserved memory regions

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Message-ID: <CAL_JsqLAxTF6DgwHNN94iQyds-rmchKS4Tx+8U7sSbAvGHMg9Q@mail.gmail.com>
Date:	Mon, 9 Nov 2015 22:41:58 -0600
From:	Rob Herring <robh+dt@...nel.org>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	Mitchel Humpherys <mitchelh@...eaurora.org>,
	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2] of: Check for overlap in reserved memory regions

On Mon, Nov 9, 2015 at 10:29 PM, Michael Ellerman <mpe@...erman.id.au> wrote:
> On Tue, 2015-09-15 at 18:30 -0700, Mitchel Humpherys wrote:
>
>> Any overlap in the reserved memory regions (those specified in the
>> reserved-memory DT node) is a bug.  These bugs might go undetected as
>> long as the contested region isn't used simultaneously by multiple
>> software agents, which makes such bugs hard to debug.  Fix this by
>> printing a scary warning during boot if overlap is detected.
>>
>> diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
>> index 726ebe792813..62f467b8ccae 100644
>> --- a/drivers/of/of_reserved_mem.c
>> +++ b/drivers/of/of_reserved_mem.c
>> @@ -197,12 +198,52 @@ static int __init __reserved_mem_init_node(struct reserved_mem *rmem)
>>       return -ENOENT;
>>  }
>>
>> +static int __init __rmem_cmp(const void *a, const void *b)
>> +{
>> +     const struct reserved_mem *ra = a, *rb = b;
>> +
>> +     return ra->base - rb->base;
>> +}
>> +
>> +static void __init __rmem_check_for_overlap(void)
>> +{
>> +     int i;
>> +
>> +     if (reserved_mem_count < 2)
>> +             return;
>> +
>> +     sort(reserved_mem, reserved_mem_count, sizeof(reserved_mem[0]),
>> +          __rmem_cmp, NULL);
>> +     for (i = 0; i < reserved_mem_count - 1; i++) {
>> +             struct reserved_mem *this, *next;
>> +
>> +             this = &reserved_mem[i];
>> +             next = &reserved_mem[i + 1];
>> +             if (!(this->base && next->base))
>> +                     continue;
>> +             if (this->base + this->size > next->base) {
>> +                     phys_addr_t this_end, next_end;
>> +
>> +                     this_end = this->base + this->size;
>> +                     next_end = next->base + next->size;
>> +                     WARN(1,
>> +                          "Reserved memory: OVERLAP DETECTED!\n%s (%pa--%pa) overlaps with %s (%pa--%pa)\n",
>> +                          this->name, &this->base, &this_end,
>> +                          next->name, &next->base, &next_end);
>
> This is blowing up on some powerpc machines.
>
> It's too early in boot to call WARN() on these systems.

I didn't realize WARN could not be used early. Good to know.

> Can we turn it into a pr_err() for now?

Sounds fine.

> I'll send a patch?

Great.

Rob
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