On Fri, Oct 02, 2026 at 04:26:43PM +0530, Shrikanth Hegde wrote: > > > On 10/2/26 1:54 PM, Michal Suchánek wrote: > > On Tue, Sep 29, 2026 at 12:46:00PM +0530, Mukesh Kumar Chaurasiya (IBM) > > wrote: > > > When running with CONFIG_PPC_IRQ_SOFT_MASK_DEBUG=y and LOCKDEP=y, an > > > Oops is triggered during NMI exit: > > > > > > [ 202.258332] Oops: Exception in kernel mode, sig: 4 [#1] > > > NIP [000000000003e178] 0x3e178 > > > LR [c00000000003e174] arch_local_irq_restore+0x2a4/0x328 > > > TRAP: 0700 MSR: 0000000000081000 <ME> > > > > > > The faulting instruction at NIP is a 'trap' (0fe00000) inside the > > > rfi_flush_fallback trampoline at a userspace-looking low address, reached > > > after a bad rfid caused by an incorrect SRR0 value. > > > > > > Root cause > > > ---------- > > > DEFINE_INTERRUPT_HANDLER_NMI used to call > > > arch_interrupt_nmi_exit_prepare() > > > *before* irqentry_nmi_exit(), giving this sequence: > > > > > > arch_interrupt_nmi_enter_prepare() // saves irq_soft_mask, > > > irq_happened > > > irqentry_nmi_enter() // __nmi_enter() -> nmi_count++, > > > in_nmi()=true > > > ____func(regs) // NMI handler body > > > arch_interrupt_nmi_exit_prepare() // RESTORES irq_soft_mask=0 > > > (IRQS_ENABLED) > > > // RESTORES irq_happened with > > > pending bits > > > irqentry_nmi_exit() // instrumentation block runs > > > here... > > > trace_hardirqs_on_prepare() // ...with in_nmi()==true still > > > lockdep_hardirqs_on_prepare() // ...and irq_soft_mask already > > > restored to 0 > > > -> arch_local_irq_restore(0) // mask=0 -> enable path entered > > > WARN_ON_ONCE(in_nmi()) // FIRES: __nmi_exit() hasn't run > > > yet > > > __nmi_exit() // nmi_count-- (too late) > > > > > > arch_interrupt_nmi_exit_prepare() restores irq_soft_mask to whatever > > > the interrupted thread had (IRQS_ENABLED / 0) and restores irq_happened > > > with any pending deferred-interrupt bits that were present when the NMI > > > fired. This is correct and necessary before rfid back to the interrupted > > > context, but it must not happen until irqentry_nmi_exit() has fully > > > completed. > > > > > > With irq_soft_mask=0 and pending bits in irq_happened, the > > > trace_hardirqs_on_prepare() call inside irqentry_nmi_exit()'s > > > instrumentation block reaches lockdep_hardirqs_on_prepare() which > > > calls __trace_hardirqs_on_caller(), which eventually calls > > > arch_local_irq_restore(0) (the IRQS_ENABLED / enable path). > > > > > > arch_local_irq_restore() with mask=0 hits the > > > CONFIG_PPC_IRQ_SOFT_MASK_DEBUG > > > guards at irq_64.c:217: > > > > > > WARN_ON_ONCE(in_nmi()); // TRUE: __nmi_exit() not yet called > > > > > > The WARN_ON_ONCE fires a 'trap' instruction (tw 31,0,0 / 0fe00000) in > > > kernel mode with MSR_PR=0, MSR_IR=0 (real-mode). The program check > > > handler (TRAP 0700) takes the sig:4 (SIGILL) path via do_program_check() > > > and calls die(), producing the Oops. > > > > > > The RESTART_TABLE mechanism in arch_local_irq_restore then causes the > > > bad rfid that lands at the userspace-looking address visible in the NIP. > > > > > > The bug is invisible with LOCKDEP=n because trace_hardirqs_on_prepare() > > > is a no-op when CONFIG_TRACE_IRQFLAGS is not set (TRACE_IRQFLAGS is > > > selected by PROVE_LOCKING which selects LOCKDEP). > > > > > > Fix > > > --- > > > > Hello, > > > > please avoid excessive formatting in commit messages. > > > > When git am is used to apply this patch it strips everything after this > > line > > Yes. Good catch. Please run ./scripts/checkpatch.pl --strict always. > > I am seeing this pattern quite often these days. > Maybe it is worth updating checkpatch.pl to catch such things. > > ERROR: Invalid commit separator - some tools may have problems applying this > #18: > ---------- > It flags this one, but if i remove that line it doesn't flag subsequent the > --- tag. > > What I would want checkpatch to see if there are multiple --- in the commit > message, > Flag it and show it as error. > > +cc Andy, Joe. Do you think that's good to fix it? > Hey Michal and Shrikanth,
Thanks, i'll fix this and send out a new vesion. Regards, Mukesh > > > > > Move arch_interrupt_nmi_exit_prepare() to after the irqentry_nmi_exit() > > > block, so that: > > > > > > irqentry_nmi_exit() // __nmi_exit() -> nmi_count--, > > > in_nmi()=false > > > arch_interrupt_nmi_exit_prepare() // now safe to restore soft mask > > > state > > > > > > The instrumentation inside irqentry_nmi_exit() now executes while > > > in_nmi() is still true (nmi_count not yet decremented), but > > > irq_soft_mask is still IRQS_ALL_DISABLED (NMI-entry value), so > > > arch_local_irq_restore() is never called with mask=0 from that path. > > > After __nmi_exit() returns, arch_interrupt_nmi_exit_prepare() restores > > > the pre-NMI soft mask and irq_happened, which is the correct state for > > > the rfid back to the interrupted context. > > > > > > Reported-by: Venkat Rao Bagalkote <[email protected]> > > > Closes: > > > https://lore.kernel.org/all/[email protected]/ > > > Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") > > > Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]> > > > --- > > > > because it's the same as this line that marks the end of the commit > > message. > > > > Thanks > > > > Michal > > > > > arch/powerpc/include/asm/interrupt.h | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/arch/powerpc/include/asm/interrupt.h > > > b/arch/powerpc/include/asm/interrupt.h > > > index 1b45a49e9bed..56f855c6f07e 100644 > > > --- a/arch/powerpc/include/asm/interrupt.h > > > +++ b/arch/powerpc/include/asm/interrupt.h > > > @@ -301,7 +301,6 @@ interrupt_handler long func(struct pt_regs *regs) > > > \ > > > state = irqentry_nmi_enter(regs); > > > \ > > > } > > > \ > > > ret = ____##func (regs); > > > \ > > > - arch_interrupt_nmi_exit_prepare(regs, &nmi_state); \ > > > if (mfmsr() & MSR_DR) { > > > \ > > > /* nmi_exit if relocations are on */ > > > \ > > > irqentry_nmi_exit(regs, state); > > > \ > > > @@ -317,6 +316,7 @@ interrupt_handler long func(struct pt_regs *regs) > > > \ > > > } else { > > > \ > > > irqentry_nmi_exit(regs, state); > > > \ > > > } > > > \ > > > + arch_interrupt_nmi_exit_prepare(regs, &nmi_state); \ > > > > > > \ > > > return ret; > > > \ > > > } > > > \ > > > -- > > > 2.55.0 > > > > > > >
