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

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Date:	Tue, 20 Jan 2015 11:35:39 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Oleg Nesterov <oleg@...hat.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Peter Zijlstra \(Intel\)" <peterz@...radead.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Prarit Bhargava <prarit@...hat.com>,
	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()

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?

Cheers,
Rusty.
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