Unverified Commit 99fd6e87 authored by Vincent Chen's avatar Vincent Chen Committed by Palmer Dabbelt
Browse files

RISC-V: Add _TIF_NEED_RESCHED check for kernel thread when CONFIG_PREEMPT=y 



The cond_resched() can be used to yield the CPU resource if
CONFIG_PREEMPT is not defined. Otherwise, cond_resched() is a dummy
function. In order to avoid kernel thread occupying entire CPU,
when CONFIG_PREEMPT=y, the kernel thread needs to follow the
rescheduling mechanism like a user thread.

Signed-off-by: default avatarVincent Chen <vincentc@andestech.com>
Tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
Signed-off-by: default avatarPalmer Dabbelt <palmer@sifive.com>
parent 49a57857

arch/riscv/kernel/asm-offsets.c

+1 −0
Original line number Diff line number Diff line
@@ -39,6 +39,7 @@ void asm_offsets(void) 
	OFFSET(TASK_STACK, task_struct, stack);

	OFFSET(TASK_TI, task_struct, thread_info);

	OFFSET(TASK_TI_FLAGS, task_struct, thread_info.flags);

	OFFSET(TASK_TI_PREEMPT_COUNT, task_struct, thread_info.preempt_count);

	OFFSET(TASK_TI_KERNEL_SP, task_struct, thread_info.kernel_sp);

	OFFSET(TASK_TI_USER_SP, task_struct, thread_info.user_sp);

	OFFSET(TASK_TI_CPU, task_struct, thread_info.cpu);

arch/riscv/kernel/entry.S

+17 −1
Original line number Diff line number Diff line
@@ -144,6 +144,10 @@ _save_context: 
	REG_L x2,  PT_SP(sp)

	.endm



#if !IS_ENABLED(CONFIG_PREEMPT)

.set resume_kernel, restore_all

#endif



ENTRY(handle_exception)

	SAVE_ALL
@@ -228,7 +232,7 @@ ret_from_exception: 
	REG_L s0, PT_SSTATUS(sp)

	csrc sstatus, SR_SIE

	andi s0, s0, SR_SPP

	bnez s0, restore_all

	bnez s0, resume_kernel



resume_userspace:

	/* Interrupts must be disabled here so flags are checked atomically */
@@ -250,6 +254,18 @@ restore_all: 
	RESTORE_ALL

	sret



#if IS_ENABLED(CONFIG_PREEMPT)

resume_kernel:

	REG_L s0, TASK_TI_PREEMPT_COUNT(tp)

	bnez s0, restore_all

need_resched:

	REG_L s0, TASK_TI_FLAGS(tp)

	andi s0, s0, _TIF_NEED_RESCHED

	beqz s0, restore_all

	call preempt_schedule_irq

	j need_resched

#endif



work_pending:

	/* Enter slow path for supplementary processing */

	la ra, ret_from_exception

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