| Message ID | alpine.LSU.2.11.2005011253250.3734@eggly.anvils (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | 5.7-rc interrupt_return Unrecoverable exception 380 | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/apply_patch | success | Successfully applied on branch powerpc/merge (54dc28ff5e0b3585224d49a31b53e030342ca5c3) |
| snowpatch_ozlabs/build-ppc64le | success | Build succeeded |
| snowpatch_ozlabs/build-ppc64be | success | Build succeeded |
| snowpatch_ozlabs/build-ppc64e | success | Build succeeded |
| snowpatch_ozlabs/build-pmac32 | warning | Upstream build failed, couldn't test patch |
| snowpatch_ozlabs/checkpatch | warning | total: 1 errors, 0 warnings, 0 checks, 8 lines checked |
| snowpatch_ozlabs/needsstable | success | Patch has no Fixes tags |
Excerpts from Hugh Dickins's message of May 2, 2020 6:38 am: > Hi Nick, > > I've been getting an "Unrecoverable exception 380" after a few hours > of load on the G5 (yes, that G5!) with 5.7-rc: when interrupt_return > checks lazy_irq_pending, it crashes at check_preemption_disabled+0x24 > with CONFIG_DEBUG_PREEMPT=y. > > check_preemption_disabled(): > lib/smp_processor_id.c:13 > 0: 7c 08 02 a6 mflr r0 > 4: fb e1 ff f8 std r31,-8(r1) > 8: fb 61 ff d8 std r27,-40(r1) > c: fb 81 ff e0 std r28,-32(r1) > 10: fb a1 ff e8 std r29,-24(r1) > 14: fb c1 ff f0 std r30,-16(r1) > get_current(): > arch/powerpc/include/asm/current.h:20 > 18: eb ed 01 88 ld r31,392(r13) > check_preemption_disabled(): > lib/smp_processor_id.c:13 > 1c: f8 01 00 10 std r0,16(r1) > 20: f8 21 ff 61 stdu r1,-160(r1) > __read_once_size(): > include/linux/compiler.h:199 > 24: 81 3f 00 00 lwz r9,0(r31) > check_preemption_disabled(): > lib/smp_processor_id.c:14 > 28: a3 cd 00 02 lhz r30,2(r13) > > I don't read ppc assembly, and have not jotted down the registers, > but hope you can make sense of it. I get around it with the patch > below (just avoiding the debug), but have no idea whether it's a > necessary fix or a hacky workaround. Hi Hugh, Thanks for the report, nice catch. Your fix is actually the correct one (well, we probably want a __lazy_irq_pending() variant which is to be used in these cases). Problem is MSR[RI] is cleared here, ready to do the last few things for interrupt return where we're not allowed to take any other interrupts. SLB interrupts can happen just about anywhere aside from kernel text, global variables, and stack. When that hits, it appears to be unrecoverable due to RI=0. We could clear just MSR[EE] for asynchronous interrupts, then check lazy_irq_pending(), and then clear MSR[RI] ready to return, and the SLB miss in the debug check would be fine. But that's two mtmsr instructions, which is slower. So we'll skip the check. I tested hash, and preempt, possibly even preempt+hash, but clearly not preempt+preempt_debug+hash+slb thrashing! Thanks, Nick > > Hugh > > --- 5.7-rc3/arch/powerpc/include/asm/hw_irq.h 2020-04-12 16:24:29.802769727 -0700 > +++ linux/arch/powerpc/include/asm/hw_irq.h 2020-04-27 11:31:10.000000000 -0700 > @@ -252,7 +252,7 @@ static inline bool arch_irqs_disabled(vo > > static inline bool lazy_irq_pending(void) > { > - return !!(get_paca()->irq_happened & ~PACA_IRQ_HARD_DIS); > + return !!(local_paca->irq_happened & ~PACA_IRQ_HARD_DIS); > } > > /* >
--- 5.7-rc3/arch/powerpc/include/asm/hw_irq.h 2020-04-12 16:24:29.802769727 -0700 +++ linux/arch/powerpc/include/asm/hw_irq.h 2020-04-27 11:31:10.000000000 -0700 @@ -252,7 +252,7 @@ static inline bool arch_irqs_disabled(vo static inline bool lazy_irq_pending(void) { - return !!(get_paca()->irq_happened & ~PACA_IRQ_HARD_DIS); + return !!(local_paca->irq_happened & ~PACA_IRQ_HARD_DIS); } /*