On Tue, Feb 18, 2025 at 10:02:03AM +0100, Marco Crivellari wrote: > 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. > > Signed-off-by: Marco Crivellari <marco.crivellari@xxxxxxxx> > --- > arch/mips/kernel/genex.S | 39 +++++++++++++++++++++------------------ > arch/mips/kernel/idle.c | 1 - > 2 files changed, 21 insertions(+), 19 deletions(-) > > diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S > index a572ce36a24f..9747b216648f 100644 > --- a/arch/mips/kernel/genex.S > +++ b/arch/mips/kernel/genex.S > @@ -104,25 +104,27 @@ handle_vcei: > > __FINIT > > - .align 5 /* 32 byte rollback region */ > + .align 5 > 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 My quick search didnn't find the reason for the extra NOPs on MICROMIPS, but they are here for a purpose. I might still need them... > + /* start of idle interrupt region */ > + MFC0 t0, CP0_STATUS > + /* Enable Interrput */ > + ori t0, 0x1f > + xori t0, 0x1e > + MTC0 t0, CP0_STATUS > + _ssnop > + _ssnop > + _ssnop instead of handcoded hazard nops, use __irq_enable_hazard for that > .set MIPS_ISA_ARCH_LEVEL_RAW > + /* > + * If an interrupt lands here, between enabling interrupts above and > + * 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. > + */ > wait > /* end of rollback region (the region size must be power of two) */ > 1: > @@ -136,9 +138,10 @@ LEAF(__r4k_wait) > .set push > .set noat > MFC0 k0, CP0_EPC > - PTR_LA k1, __r4k_wait > - ori k0, 0x1f /* 32 byte rollback region */ > - xori k0, 0x1f > + PTR_LA k1, 1b > + /* 32 byte idle interrupt region */ > + ori k0, 0x1f > + daddiu k0, 1 /local/tbogendoerfer/korg/linux/arch/mips/kernel/genex.S: Assembler messages: /local/tbogendoerfer/korg/linux/arch/mips/kernel/genex.S:151: Error: opcode not supported on this processor: mips32r2 (mips32r2) `daddiu $26,1' /local/tbogendoerfer/korg/linux/arch/mips/kernel/genex.S:271: Error: opcode not supported on this processor: mips32r2 (mips32r2) `daddiu $26,1' looks like you haven't compiled this code for 32bit. Use PTR_ADDIU, which will use the correct instuction for 32 and 64bit. But I doubt this works, because the wait instruction is not aligned to a 32 byte boundary, but the code assuemes this, IMHO. Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]
