Le Wed, Mar 19, 2025 at 12:07:07PM +0100, Thomas Bogendoerfer a écrit : > On Sat, Mar 15, 2025 at 08:40:02PM +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. > > can you give a commit ID, when this change got introduced ? > > > 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. > > > > Signed-off-by: Marco Crivellari <marco.crivellari@xxxxxxxx> > > --- > > arch/mips/kernel/genex.S | 42 ++++++++++++++++++++++------------------ > > arch/mips/kernel/idle.c | 1 - > > 2 files changed, 23 insertions(+), 20 deletions(-) > > > > diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S > > index a572ce36a24f..4e012421d00f 100644 > > --- a/arch/mips/kernel/genex.S > > +++ b/arch/mips/kernel/genex.S > > @@ -104,27 +104,30 @@ 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 > > + /* Start of idle interrupt region. */ > > + MFC0 t0, CP0_STATUS > > + /* Enable interrupt. */ > > + ori t0, 0x1f > > + xori t0, 0x1e > > + MTC0 t0, CP0_STATUS > > + _ssnop > > + _ssnop > > + _ssnop > > + _ehb > > .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) */ > > + /* End of idle interrupt region. */ > > 1: > > please give this label a name for example __r4k_wait_exit and do a > runtime check that it really has 36 bytes offset to __r4k_wait Where would be the best place for that? arch/mips/kernel/setup.c:setup_arch() maybe? Thanks.
