linux-kernel - Re: [RFC/PATCH] init/main.c: Simplify initcall

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Date:	Tue, 20 Jan 2015 05:49:54 -0500
From:	Prarit Bhargava <prarit@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Oleg Nesterov <oleg@...hat.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Fabian Frederick <fabf@...net.be>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC/PATCH] init/main.c: Simplify initcall_blacklisted()



On 01/19/2015 08:05 PM, Rusty Russell wrote:
> Oleg Nesterov <oleg@...hat.com> writes:
>> On 01/17, Rasmus Villemoes wrote:
>>>
>>> Using kasprintf to get the function name makes us look up the name
>>> twice, along with all the vsnprintf overhead of parsing the format
>>> string etc. It also means there is an allocation failure case to deal
>>> with. Since symbol_string in vsprintf.c would anyway allocate an array
>>> of size KSYM_SYMBOL_LEN on the stack, that might as well be done up
>>> here.
>>>
>>> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
>>> ---
>>>
>>> Notes:
>>>     I don't know how expensive it is to do the symbol lookup for each
>>>     initcall. It might be worthwhile adding an
>>>     
>>>       if (list_empty(&blacklisted_initcalls))
>>>         return false;
>>>     
>>>     at the very beginning of initcall_blacklisted(), since this is a debug
>>>     feature and the blacklist is indeed usually empty.
>>
>> If we want to optimize this... I am wondering if we can change
>> initcall_blacklist()
>>
>> 	-	entry->buf = alloc_bootmem(strlen(str_entry) + 1);
>> 	+	ebtry->fn = kallsyms_lookup_name(str_entry);
>>
>> and then change initcall_blacklisted() to just compare the pointers.
> 
> That would make far, far more sense.  It would fail for modules of
> course, but that might be OK.  Prarit, this was your code; does it
> matter?

It does actually matter to me.  I've been using it to blacklist modules at boot
as well ... and it works really well :)  So I'm okay with the original patch but
not the second suggested change.

P.

> 
> Cheers,
> Rusty.
> 
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