linux-kernel - Re: [RFC PATCH v3 5/7] powerpc: 'current_set' is now a table of task

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Date:   Wed, 3 Oct 2018 08:00:43 +0200
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        aneesh.kumar@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v3 5/7] powerpc: 'current_set' is now a table of
 task_struct pointers



Le 03/10/2018 à 07:41, Nicholas Piggin a écrit :
> On Mon,  1 Oct 2018 12:30:27 +0000 (UTC)
> Christophe Leroy <christophe.leroy@....fr> wrote:
> 
>> The table of pointers 'current_set' has been used for retrieving
>> the stack and current. They used to be thread_info pointers as
>> they were pointing to the stack and current was taken from the
>> 'task' field of the thread_info.
>>
>> Now, the pointers of 'current_set' table are now both pointers
>> to task_struct and pointers to thread_info.
>>
>> As they are used to get current, and the stack pointer is
>> retrieved from current's stack field, this patch changes
>> their type to task_struct, and renames secondary_ti to
>> secondary_current.
> 
> I'm not sure if current_set is actually needed is it? Because
> 64-bit already initializes paca->ksave / PACAKSAVE. That might
> be a cleanup to do after your series.

head_64.S contains:

__secondary_start:
	/* Set thread priority to MEDIUM */
	HMT_MEDIUM

	/* Initialize the kernel stack */
	LOAD_REG_ADDR(r3, current_set)
	sldi	r28,r24,3		/* get current_set[cpu#]	 */
	ldx	r14,r3,r28
	addi	r14,r14,THREAD_SIZE-STACK_FRAME_OVERHEAD
	std	r14,PACAKSAVE(r13)


32-bit doesn't seem to use it, it only uses secondary_ti it seems.

> 
> Reviewed-by: Nicholas Piggin <npiggin@...il.com>
> 

Christophe