On Wed, Jan 23, 2019 at 02:58:51AM +0800, Palmer Dabbelt wrote: > On Wed, 02 Jan 2019 21:45:55 PST (-0800), linux@xxxxxxxxxxxx wrote: > > On Thu, Jan 03, 2019 at 11:32:33AM +0800, Vincent Chen wrote: > >> 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: Vincent Chen <vincentc@xxxxxxxxxxxxx> > > > > This patch seems to do the trick. I no longer see a problem with > > CONFIG_PREEMPT=y and the various lock torture tests enabled, as > > previously reported. > > > > Nice catch and fix. > > > > Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx> > > > > Guenter > > > >> --- > >> arch/riscv/kernel/asm-offsets.c | 1 + > >> arch/riscv/kernel/entry.S | 18 +++++++++++++++++- > >> 2 files changed, 18 insertions(+), 1 deletions(-) > >> > >> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c > >> index 6a92a2f..dac9834 100644 > >> --- a/arch/riscv/kernel/asm-offsets.c > >> +++ b/arch/riscv/kernel/asm-offsets.c > >> @@ -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); > >> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S > >> index 13d4826..728b72d 100644 > >> --- a/arch/riscv/kernel/entry.S > >> +++ b/arch/riscv/kernel/entry.S > >> @@ -144,6 +144,10 @@ _save_context: > >> REG_L x2, PT_SP(sp) > >> .endm > >> > >> +#if !IS_ENABLED(CONFIG_PREEMPT) > >> +#define resume_kernel restore_all > >> +#endif > >> + > > I don't like preprocessor stuff if we can avoid it, are you OK if I squash in > the following diff: > > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S > index cfbad2f689c3..fd9b57c8b4ce 100644 > --- a/arch/riscv/kernel/entry.S > +++ b/arch/riscv/kernel/entry.S > @@ -145,7 +145,7 @@ _save_context: > .endm > > #if !IS_ENABLED(CONFIG_PREEMPT) > -#define resume_kernel restore_all > +.set resume_kernel, restore_all > #endif > > ENTRY(handle_exception) > > I think that should do the same thing, but at link time instead of in the > preprocessor -- that makes it a bit less likely to bit us in the future. > > >> 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 > > I'm just going to assume you're OK with the squash and drop this into my plans > for the next RC, let me know if that's not OK. > > Thanks for fixing this! OK, it's fine for me. Vincent
