From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Date: Fri, 19 May 2023 16:57:31 +0200 Subject: [PATCH 5/5] ARM: vfp: Use vfp_lock() in vfp_entry(). vfp_entry() is invoked from exception handler and is fully preemptible. It uses local_bh_disable() to remain uninterrupted while checking the VFP state. This is not working on PREEMPT_RT because local_bh_disable() synchronizes the relevant section but the context remains fully preemptible. Use vfp_lock() for uninterrupted access. VFP_bounce() is invoked from within vfp_entry() and may send a signal. Sending a signal uses spinlock_t which becomes a sleeping lock on PREEMPT_RT and must not be acquired within a preempt-disabled section. Move the vfp_raise_sigfpe() block outside of the preempt-disabled section. Link: https://lore.kernel.org/r/20230519145731.574867-4-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- arch/arm/vfp/vfphw.S | 7 ++----- arch/arm/vfp/vfpmodule.c | 30 ++++++++++++++++++++---------- 2 files changed, 22 insertions(+), 15 deletions(-) Index: linux-6.3.1-rt13/arch/arm/vfp/vfphw.S =================================================================== @ linux-6.3.1-rt13/arch/arm/vfp/vfphw.S:183 @ vfp_hw_state_valid: @ always subtract 4 from the following @ instruction address. -local_bh_enable_and_ret: - adr r0, . - mov r1, #SOFTIRQ_DISABLE_OFFSET - b __local_bh_enable_ip @ tail call + b vfp_exit @ tail call look_for_VFP_exceptions: @ Check for synchronous or asynchronous exception @ linux-6.3.1-rt13/arch/arm/vfp/vfphw.S:206 @ skip: @ not recognised by VFP DBGSTR "not VFP" - b local_bh_enable_and_ret + b vfp_exit @ tail call process_exception: DBGSTR "bounce" Index: linux-6.3.1-rt13/arch/arm/vfp/vfpmodule.c =================================================================== --- linux-6.3.1-rt13.orig/arch/arm/vfp/vfpmodule.c +++ linux-6.3.1-rt13/arch/arm/vfp/vfpmodule.c @ linux-6.3.1-rt13/arch/arm/vfp/vfphw.S:270 @ static void vfp_panic(char *reason, u32 /* * Process bitmask of exception conditions. */ -static void vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr, struct pt_regs *regs) +static int vfp_raise_exceptions(u32 exceptions, u32 inst, u32 fpscr) { int si_code = 0; @ linux-6.3.1-rt13/arch/arm/vfp/vfphw.S:278 @ static void vfp_raise_exceptions(u32 exc if (exceptions == VFP_EXCEPTION_ERROR) { vfp_panic("unhandled bounce", inst); - vfp_raise_sigfpe(FPE_FLTINV, regs); - return; + return FPE_FLTINV; } /* @ linux-6.3.1-rt13/arch/arm/vfp/vfphw.S:306 @ static void vfp_raise_exceptions(u32 exc RAISE(FPSCR_OFC, FPSCR_OFE, FPE_FLTOVF); RAISE(FPSCR_IOC, FPSCR_IOE, FPE_FLTINV); - if (si_code) - vfp_raise_sigfpe(si_code, regs); + return si_code; } /* @ linux-6.3.1-rt13/arch/arm/vfp/vfphw.S:351 @ static u32 vfp_emulate_instruction(u32 i void VFP_bounce(u32 trigger, u32 fpexc, struct pt_regs *regs) { u32 fpscr, orig_fpscr, fpsid, exceptions; + int si_code2 = 0; + int si_code = 0; pr_debug("VFP: bounce: trigger %08x fpexc %08x\n", trigger, fpexc); @ linux-6.3.1-rt13/arch/arm/vfp/vfphw.S:400 @ void VFP_bounce(u32 trigger, u32 fpexc, * unallocated VFP instruction but with FPSCR.IXE set and not * on VFP subarch 1. */ - vfp_raise_exceptions(VFP_EXCEPTION_ERROR, trigger, fpscr, regs); + si_code = vfp_raise_exceptions(VFP_EXCEPTION_ERROR, trigger, fpscr); goto exit; } @ linux-6.3.1-rt13/arch/arm/vfp/vfphw.S:425 @ void VFP_bounce(u32 trigger, u32 fpexc, */ exceptions = vfp_emulate_instruction(trigger, fpscr, regs); if (exceptions) - vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs); + si_code2 = vfp_raise_exceptions(exceptions, trigger, orig_fpscr); /* * If there isn't a second FP instruction, exit now. Note that @ linux-6.3.1-rt13/arch/arm/vfp/vfphw.S:444 @ void VFP_bounce(u32 trigger, u32 fpexc, emulate: exceptions = vfp_emulate_instruction(trigger, orig_fpscr, regs); if (exceptions) - vfp_raise_exceptions(exceptions, trigger, orig_fpscr, regs); + si_code = vfp_raise_exceptions(exceptions, trigger, orig_fpscr); + exit: - local_bh_enable(); + vfp_unlock(); + if (si_code2) + vfp_raise_sigfpe(si_code2, regs); + if (si_code) + vfp_raise_sigfpe(si_code, regs); } static void vfp_enable(void *unused) @ linux-6.3.1-rt13/arch/arm/vfp/vfphw.S:692 @ asmlinkage void vfp_entry(u32 trigger, s if (unlikely(!have_vfp)) return; - local_bh_disable(); + vfp_lock(); vfp_support_entry(trigger, ti, resume_pc, resume_return_address); } +asmlinkage void vfp_exit(void) +{ + vfp_unlock(); +} + #ifdef CONFIG_KERNEL_MODE_NEON static int vfp_kmode_exception(struct pt_regs *regs, unsigned int instr)