Commit 56651128 authored by Marco Crivellari's avatar Marco Crivellari Committed by Thomas Bogendoerfer
Browse files

MIPS: Fix idle VS timer enqueue 



MIPS re-enables interrupts on its idle routine and performs
a TIF_NEED_RESCHED check afterwards before putting the CPU to sleep.

The IRQs firing between the check and the 'wait' instruction may set the
TIF_NEED_RESCHED flag. In order to deal with this possible race, IRQs
interrupting __r4k_wait() rollback their return address to the
beginning of __r4k_wait() so that TIF_NEED_RESCHED is checked
again before going back to sleep.

However idle IRQs can also queue timers that may require a tick
reprogramming through a new generic idle loop iteration but those timers
would go unnoticed here because __r4k_wait() only checks
TIF_NEED_RESCHED. It doesn't check for pending timers.

Fix this with fast-forwarding idle IRQs return address to the end of the
idle routine instead of the beginning, so that the generic idle loop
handles both TIF_NEED_RESCHED and pending timers.

CONFIG_CPU_MICROMIPS has been removed along with the nop instructions.
There, NOPs are 2 byte in size, so change the code with 3 _ssnop which are
always 4 byte and remove the ifdef. Added ehb to make sure the hazard
is always cleared.

Fixes: c65a5480 ("[MIPS] Fix potential latency problem due to non-atomic cpu_wait.")
Signed-off-by: default avatarMarco Crivellari <marco.crivellari@suse.com>
Signed-off-by: default avatarMaciej W. Rozycki <macro@orcam.me.uk>
Acked-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarThomas Bogendoerfer <tsbogend@alpha.franken.de>
parent 0af2f6be

arch/mips/include/asm/idle.h

+1 −2
Original line number Diff line number Diff line
@@ -6,8 +6,7 @@ 
#include <linux/linkage.h>



extern void (*cpu_wait)(void);

extern void r4k_wait(void);

extern asmlinkage void __r4k_wait(void);

extern asmlinkage void r4k_wait(void);

extern void r4k_wait_irqoff(void);



static inline int using_rollback_handler(void)

arch/mips/kernel/genex.S

+36 −26
Original line number Diff line number Diff line
@@ -104,42 +104,52 @@ handle_vcei: 


	__FINIT



	.align	5	/* 32 byte rollback region */

LEAF(__r4k_wait)

	.set	push

	.set	noreorder

	/* start of rollback region */

	LONG_L	t0, TI_FLAGS($28)

	nop

	andi	t0, _TIF_NEED_RESCHED

	bnez	t0, 1f

	 nop

	nop

	nop

#ifdef CONFIG_CPU_MICROMIPS

	nop

	nop

	nop

	nop

#endif

	/* Align to 32 bytes for the maximum idle interrupt region size. */

	.align	5

LEAF(r4k_wait)

	/* Keep the ISA bit clear for calculations on local labels here. */

0:	.fill 	0

	/* Start of idle interrupt region. */

	local_irq_enable

	/*

	 * If an interrupt lands here, before going idle on the next

	 * instruction, we must *NOT* go idle since the interrupt could

	 * have set TIF_NEED_RESCHED or caused a timer to need resched.

	 * Fall through -- see rollback_handler below -- and have the

	 * idle loop take care of things.

	 */

1:	.fill	0

	/* The R2 EI/EHB sequence takes 8 bytes, otherwise pad up.  */

	.if		1b - 0b > 32

	.error	"overlong idle interrupt region"

	.elseif	1b - 0b > 8

	.align	4

	.endif

2:	.fill	0

	.equ	r4k_wait_idle_size, 2b - 0b

	/* End of idle interrupt region; size has to be a power of 2. */

	.set	MIPS_ISA_ARCH_LEVEL_RAW

r4k_wait_insn:

	wait

	/* end of rollback region (the region size must be power of two) */

1:

r4k_wait_exit:

	.set	mips0

	local_irq_disable

	jr	ra

	 nop

	.set	pop

	END(__r4k_wait)

	END(r4k_wait)

	.previous



	.macro	BUILD_ROLLBACK_PROLOGUE handler

	FEXPORT(rollback_\handler)

	.set	push

	.set	noat

	MFC0	k0, CP0_EPC

	PTR_LA	k1, __r4k_wait

	ori	k0, 0x1f	/* 32 byte rollback region */

	xori	k0, 0x1f

	/* Subtract/add 2 to let the ISA bit propagate through the mask.  */

	PTR_LA	k1, r4k_wait_insn - 2

	ori 	k0, r4k_wait_idle_size - 2

	.set	noreorder

	bne	k0, k1, \handler

	PTR_ADDIU 	k0, r4k_wait_exit - r4k_wait_insn + 2

	.set	reorder

	MTC0	k0, CP0_EPC

	.set pop

	.endm

arch/mips/kernel/idle.c

+0 −7
Original line number Diff line number Diff line
@@ -35,13 +35,6 @@ static void __cpuidle r3081_wait(void) 
	write_c0_conf(cfg | R30XX_CONF_HALT);

}



void __cpuidle r4k_wait(void)

{

	raw_local_irq_enable();

	__r4k_wait();

	raw_local_irq_disable();

}



/*

 * This variant is preferable as it allows testing need_resched and going to

 * sleep depending on the outcome atomically.  Unfortunately the "It is