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Re: [Xen-devel] [PATCH v2] CODING_STYLE: Document how to handle unexpected conditions
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: George Dunlap <george.dunlap@xxxxxxxxxx>
- Date: Fri, 6 Dec 2019 14:12:38 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Wilk <konrad.wilk@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 06 Dec 2019 14:13:04 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 12/6/19 12:17 PM, Jan Beulich wrote:
> On 06.12.2019 12:48, George Dunlap wrote:
>> --- a/CODING_STYLE
>> +++ b/CODING_STYLE
>> @@ -133,3 +133,86 @@ the end of files. It should be:
>> * indent-tabs-mode: nil
>> * End:
>> */
>> +
>> +Handling unexpected conditions
>> +------------------------------
>> +
>> +GUIDELINES:
>> +
>> +Passing errors up the stack should be used when the caller is already
>> +expecting to handle errors, and the state when the error was
>> +discovered isn’t broken, or too isn't hard to fix.
>
> Was the "too" meant to come later in the sentence?
I did actually go through this several times; I don't have any idea how
I managed to miss all these editing mistakes! All editing comments are
"ack" unless otherwise mentioned.
>> +domain_crash() should be used when passing errors up the stack is too
>> +difficult, and/or when fixing up state of a guest is impractical, but
>> +where fixing up the state of Xen will allow Xen to continue running.
>> +
>> +BUG_ON() should be used when you can’t pass errors up the stack, and
>> +either continuing or crashing the guest would likely cause an
>> +information leak or privilege escalation vulnerability.
>
> Strictly speaking BUG_ON() isn't an error handling mechanism either.
> Further down it becomes more clear (it rather to be used for
> detecting broken assumptions), but I guess it wouldn't hurt to say
> so here as well.
I guess it depends on what you mean by "error handling mechanism". The
BUG_ON() in page_alloc.c has reliably changed potential privilege
escalations into "mere" DoSes over the years.
The distinction I'm trying to draw between BUG_ON() and ASSERT() is that
BUG_ON() actually handles the situation (albeit with a very heavy
hammer). ASSERT() is essentially a more noticeable printk.
-George
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