On 2015-02-20 20:52, Philippe Gerum wrote:
> On 02/20/2015 08:47 PM, Philippe Gerum wrote:
>> On 02/20/2015 08:44 PM, Philippe Gerum wrote:
>>> On 02/20/2015 07:17 PM, Jan Kiszka wrote:
>>>> On 2015-02-20 19:03, Jan Kiszka wrote:
>>>>> Hi Gilles,
>>>>>
>>>>> analyzing a lockdep warning on 3.16 with I-pipe enabled, I dug deeper
>>>>> into the hard and virtual interrupt state management during exception
>>>>> handling on ARM. I think there are several issues:
>>>>>
>>>>> - ipipe_fault_entry should not fiddle with the root irq state if run
>>>>> over head, only when invoked over root.
>>>>> - ipipe_fault_exit must not change the root state unless we entered over
>>>>> head and are about to leave over root - see x86. The current code may
>>>>> keep root incorrectly stalled after an exception, though this will
>>>>> probably be fixed up again in practice quickly.
>>>>
>>>> And the adjustment of the root irq state after migration has to happen
>>>> before Linux starts to handle the event. It would basically be a late
>>>> ipipe_fault_entry.
>>>>
>>>>> - do_sect_fault is only called by do_DataAbort and do_PrefetchAbort,
>>>>> in both cases already wrapped in ipipe_fault_entry/exit, thus it
>>>>> shouldn't invoke them once again.
>>>>
>>>> Sorry, this was a misinterpretation - do_sect_fault is invoked before
>>>> ipipe_fault_entry.
>>>>
>>>> What I need to add, though:
>>>>
>>>> - do_DataAbort and do_PrefetchAbort call __ipipe_report_trap after
>>>> ipipe_fault_entry, thus with hard IRQs on.
>>>
>>> This would break LPAE with the Xenomai nucleus as a module on 2.6.x, by
>>> treading over a non-linear kernel mapping before the page table could be
>>> fixed up. do_translation_fault() must run via the fsr handler
>>> indirection before any non-linear access.
>>>
>>
>> Sorry, if you do that _after_ the fault entry notification, then it's ok
>> in theory. However, I don't understand why we would need to notify when
>> only a minor fixup is required, that does not entail a mode migration.
>>
>
> To be clearer, do you intend to report the minor fault upon
> do_translation_fault() returning zero, or are you referring to a
> different context?
No, I'm just talking about this potential change:
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 38834c6..b42632a 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -629,10 +629,10 @@ do_DataAbort(unsigned long addr, unsigned int fsr, struct
pt_regs *regs)
if (!inf->fn(addr, fsr & ~FSR_LNX_PF, regs))
return;
- irqflags = ipipe_fault_entry();
-
if (__ipipe_report_trap(IPIPE_TRAP_UNKNOWN, regs))
- goto out;
+ return;
+
+ irqflags = ipipe_fault_entry();
printk(KERN_ALERT "Unhandled fault: %s (0x%03x) at 0x%08lx\n",
inf->name, fsr, addr);
@@ -642,7 +642,7 @@ do_DataAbort(unsigned long addr, unsigned int fsr, struct
pt_regs *regs)
info.si_code = inf->code;
info.si_addr = (void __user *)addr;
arm_notify_die("", regs, &info, fsr, 0);
-out:
+
ipipe_fault_exit(irqflags);
}
@@ -669,10 +669,10 @@ do_PrefetchAbort(unsigned long addr, unsigned int ifsr,
struct pt_regs *regs)
if (!inf->fn(addr, ifsr | FSR_LNX_PF, regs))
return;
- irqflags = ipipe_fault_entry();
-
if (__ipipe_report_trap(IPIPE_TRAP_UNKNOWN, regs))
- goto out;
+ return;
+
+ irqflags = ipipe_fault_entry();
printk(KERN_ALERT "Unhandled prefetch abort: %s (0x%03x) at 0x%08lx\n",
inf->name, ifsr, addr);
@@ -682,7 +682,7 @@ do_PrefetchAbort(unsigned long addr, unsigned int ifsr,
struct pt_regs *regs)
info.si_code = inf->code;
info.si_addr = (void __user *)addr;
arm_notify_die("", regs, &info, ifsr, 0);
-out:
+
ipipe_fault_exit(irqflags);
}
This seems more consistent - if not more correct - as it now does the
reporting with hard irqs off, like in the other cases.
Jan
--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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