* [PATCH] ARM: Stop irqsoff tracing if return to user with interrupts enabled
2010-11-13 8:48 ` Russell King - ARM Linux
@ 2010-11-13 9:35 ` Todd Poynor
2010-11-13 9:38 ` Russell King - ARM Linux
1 sibling, 0 replies; 4+ messages in thread
From: Todd Poynor @ 2010-11-13 9:35 UTC (permalink / raw)
To: linux-arm-kernel
On Sat, Nov 13, 2010 at 12:48 AM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Fri, Nov 12, 2010 at 07:40:48PM -0800, Todd Poynor wrote:
>> Signed-off-by: Todd Poynor <toddpoynor@google.com>
>
> NAK. ?Firstly, you're not explaining why. ?Secondly, we purposely leave
> IRQs off when returning to userspace to avoid race conditions. ?Thirdly,
> we purposely leave lockdep believing that IRQs are off while userspace
> is running, even though IRQs are not.
Apologies for the lack of explanation. The change makes the irqsoff
tracer account for whether the return to userspace will or will not
enable interrupts; it will not override the kernel's decision on
interrupts being enabled or not, and I don't believe it will affect
lockdep's beliefs.
The reason why is to properly terminate an IRQs-disabled interval if
IRQs will in fact be enabled on return, so that the tracer does not
continue to measure the time spent in userspace as a continuation of
the IRQs-off sequence started by the call to disable_irq at
ret_slow_syscall or ret_fast_syscall. The x86 architecture implements
macro TRACE_IRQS_IRET for the same purpose.
I'll continue to search the lists in case there's anything I've missed.
>
> I've explained why this is in the past - please search the mailing list.
>
>> ---
>> ?arch/arm/kernel/entry-common.S | ? 14 ++++++++++++++
>> ?1 files changed, 14 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
>> index 8bfa987..b81d270 100644
>> --- a/arch/arm/kernel/entry-common.S
>> +++ b/arch/arm/kernel/entry-common.S
>> @@ -29,6 +29,13 @@ ret_fast_syscall:
>> ? ? ? ldr ? ? r1, [tsk, #TI_FLAGS]
>> ? ? ? tst ? ? r1, #_TIF_WORK_MASK
>> ? ? ? bne ? ? fast_work_pending
>> +#if defined(CONFIG_TRACE_IRQFLAGS)
>> + ? ? ldr ? ? r1, [sp, #S_OFF + S_PSR] ? ? ? ?@ get calling cpsr
>> + ? ? tst ? ? r1, #PSR_I_BIT
>> + ? ? bne ? ? 1f
>> + ? ? asm_trace_hardirqs_on
>> +1:
>> +#endif
>>
>> ? ? ? /* perform architecture specific actions before user return */
>> ? ? ? arch_ret_to_user r1, lr
>> @@ -65,6 +72,13 @@ ret_slow_syscall:
>> ? ? ? tst ? ? r1, #_TIF_WORK_MASK
>> ? ? ? bne ? ? work_pending
>> ?no_work_pending:
>> +#if defined(CONFIG_TRACE_IRQFLAGS)
>> + ? ? ldr ? ? r1, [sp, #S_PSR] ? ? ? ? ? ? ? ?@ get calling cpsr
>> + ? ? tst ? ? r1, #PSR_I_BIT
>> + ? ? bne ? ? 2f
>> + ? ? asm_trace_hardirqs_on
>> +2:
>> +#endif
>> ? ? ? /* perform architecture specific actions before user return */
>> ? ? ? arch_ret_to_user r1, lr
>>
>> --
>> 1.7.3.1
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel at lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH] ARM: Stop irqsoff tracing if return to user with interrupts enabled
2010-11-13 8:48 ` Russell King - ARM Linux
2010-11-13 9:35 ` Todd Poynor
@ 2010-11-13 9:38 ` Russell King - ARM Linux
1 sibling, 0 replies; 4+ messages in thread
From: Russell King - ARM Linux @ 2010-11-13 9:38 UTC (permalink / raw)
To: linux-arm-kernel
On Sat, Nov 13, 2010 at 08:48:02AM +0000, Russell King - ARM Linux wrote:
> On Fri, Nov 12, 2010 at 07:40:48PM -0800, Todd Poynor wrote:
> > Signed-off-by: Todd Poynor <toddpoynor@google.com>
>
> NAK. Firstly, you're not explaining why. Secondly, we purposely leave
> IRQs off when returning to userspace to avoid race conditions. Thirdly,
> we purposely leave lockdep believing that IRQs are off while userspace
> is running, even though IRQs are not.
Forthly, we never run userspace with IRQs disabled - that would be a
security hole.
> I've explained why this is in the past - please search the mailing list.
See
http://lists.arm.linux.org.uk/lurker/message/20100523.141301.a94bee0c.en.html
http://lists.arm.linux.org.uk/lurker/message/20100523.194746.203225eb.en.html
^ permalink raw reply [flat|nested] 4+ messages in thread