Re: [RFC] [patch 4/6 -rt] powerpc 2.6.20-rt8: fix a runtime warnings for xmon
On Wednesday 07 March 2007, Ingo Molnar wrote: > i'm not an xmon expert, but maybe it might make more sense to first > disable preemption, then interrupts - otherwise you could be preempted > right after having disabled these interrupts (and be scheduled to > another CPU, etc.). What is the difference between local_irq_save() and > the above 'disable interrupts' sequence? If it's not the same and > xmon_core() relied on having hardirqs disabled then it might make sense > to do a local_irq_save() there, instead of a preempt_disable(). Since relatively recently, powerpc does no longer actually disable the hardware interrupts with local_irq_disable(), but rather sets a per-cpu flag that will be checked if an actual interrupt comes in as part of the critical section. The mtmsr() sequence in xmon corresponds to hard_irq_disable() and should probably changed to that, but then you still need the extra preempt_disable() / preempt_enable(). I think you're right about the sequence having to be 1. preempt_disable() 2. hard_irq_disable() 3. 4. hard_irq_enable() 5. preempt_enable() Arnd <>< - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC] [patch 4/6 -rt] powerpc 2.6.20-rt8: fix a runtime warnings for xmon
At Wed, 07 Mar 2007 11:10:59 +0100, Benjamin Herrenschmidt wrote: > > On Wed, 2007-03-07 at 10:16 +0100, Ingo Molnar wrote: > > * Tsutomu OWA <[EMAIL PROTECTED]> wrote: > > > > > @@ -342,6 +342,7 @@ static int xmon_core(struct pt_regs *reg > > > > > > msr = mfmsr(); > > > mtmsr(msr & ~MSR_EE); /* disable interrupts */ > > > + preempt_disable(); > > > > i'm not an xmon expert, but maybe it might make more sense to first > > disable preemption, then interrupts - otherwise you could be preempted > > right after having disabled these interrupts (and be scheduled to > > another CPU, etc.). What is the difference between local_irq_save() and > > the above 'disable interrupts' sequence? If it's not the same and > > xmon_core() relied on having hardirqs disabled then it might make sense > > to do a local_irq_save() there, instead of a preempt_disable(). > > powerpc 64 bits nowadays does lazy HW masking, so local_irq_disable() > will not actually switch MSR_EE off. However, xmon needs that to happen > (though we have a nicer accessor to do it, I suspect some bitrot need > fixing in there, possibly already fixed in .21) > > I agree that preempt_disable() should be put before the MSR tweaking > though. As all of you said, I'm resending the patch here. To fix the following runtime warnings when entering xmon. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Entering xmon BUG: using smp_processor_id() in preemptible [] code: khvcd/280 caller is .xmon_core+0xb8/0x8ec Call Trace: [CFD737C0] [C000FAAC] .show_stack+0x68/0x1b0 (unreliable) [CFD73860] [C01F71F0] .debug_smp_processor_id+0xc8/0xf8 [CFD738F0] [C004AF30] .xmon_core+0xb8/0x8ec [CFD73A80] [C004B918] .xmon+0x38/0x4c [CFD73C60] [C004BA8C] .sysrq_handle_xmon+0x48/0x5c [CFD73CD0] [C0243A68] .__handle_sysrq+0xe0/0x1b0 [CFD73D70] [C0244974] .hvc_poll+0x18c/0x2b4 [CFD73E50] [C0244E80] .khvcd+0x88/0x164 [CFD73EE0] [C0075014] .kthread+0x124/0x174 [CFD73F90] [C0023D48] .kernel_thread+0x4c/0x68 BUG: khvcd:280 task might have lost a preemption check! Call Trace: [CFD73740] [C000FAAC] .show_stack+0x68/0x1b0 (unreliable) [CFD737E0] [C0054920] .preempt_enable_no_resched+0x64/0x7c [CFD73860] [C01F71F8] .debug_smp_processor_id+0xd0/0xf8 [CFD738F0] [C004AF30] .xmon_core+0xb8/0x8ec [CFD73A80] [C004B918] .xmon+0x38/0x4c [CFD73C60] [C004BA8C] .sysrq_handle_xmon+0x48/0x5c [CFD73CD0] [C0243A68] .__handle_sysrq+0xe0/0x1b0 [CFD73D70] [C0244974] .hvc_poll+0x18c/0x2b4 [CFD73E50] [C0244E80] .khvcd+0x88/0x164 [CFD73EE0] [C0075014] .kthread+0x124/0x174 [CFD73F90] [C0023D48] .kernel_thread+0x4c/0x68 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - thanks a lot! Signed-off-by: Tsutomu Owa <[EMAIL PROTECTED]> -- owa --- linux-rt8/arch/powerpc/xmon/xmon.c 2007-02-20 09:38:52.0 +0900 +++ rt/arch/powerpc/xmon/xmon.c 2007-03-07 19:49:38.0 +0900 @@ -340,6 +340,7 @@ static int xmon_core(struct pt_regs *reg unsigned long timeout; #endif + preempt_disable(); msr = mfmsr(); mtmsr(msr & ~MSR_EE); /* disable interrupts */ @@ -517,6 +518,7 @@ static int xmon_core(struct pt_regs *reg insert_cpu_bpts(); mtmsr(msr); /* restore interrupt enable */ + preempt_enable(); return cmd != 'X' && cmd != EOF; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC] [patch 4/6 -rt] powerpc 2.6.20-rt8: fix a runtime warnings for xmon
On Wed, 2007-03-07 at 10:16 +0100, Ingo Molnar wrote: > * Tsutomu OWA <[EMAIL PROTECTED]> wrote: > > > @@ -342,6 +342,7 @@ static int xmon_core(struct pt_regs *reg > > > > msr = mfmsr(); > > mtmsr(msr & ~MSR_EE); /* disable interrupts */ > > + preempt_disable(); > > i'm not an xmon expert, but maybe it might make more sense to first > disable preemption, then interrupts - otherwise you could be preempted > right after having disabled these interrupts (and be scheduled to > another CPU, etc.). What is the difference between local_irq_save() and > the above 'disable interrupts' sequence? If it's not the same and > xmon_core() relied on having hardirqs disabled then it might make sense > to do a local_irq_save() there, instead of a preempt_disable(). powerpc 64 bits nowadays does lazy HW masking, so local_irq_disable() will not actually switch MSR_EE off. However, xmon needs that to happen (though we have a nicer accessor to do it, I suspect some bitrot need fixing in there, possibly already fixed in .21) I agree that preempt_disable() should be put before the MSR tweaking though. Ben. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [RFC] [patch 4/6 -rt] powerpc 2.6.20-rt8: fix a runtime warnings for xmon
* Tsutomu OWA <[EMAIL PROTECTED]> wrote: > @@ -342,6 +342,7 @@ static int xmon_core(struct pt_regs *reg > > msr = mfmsr(); > mtmsr(msr & ~MSR_EE); /* disable interrupts */ > + preempt_disable(); i'm not an xmon expert, but maybe it might make more sense to first disable preemption, then interrupts - otherwise you could be preempted right after having disabled these interrupts (and be scheduled to another CPU, etc.). What is the difference between local_irq_save() and the above 'disable interrupts' sequence? If it's not the same and xmon_core() relied on having hardirqs disabled then it might make sense to do a local_irq_save() there, instead of a preempt_disable(). Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[RFC] [patch 4/6 -rt] powerpc 2.6.20-rt8: fix a runtime warnings for xmon
To fix the following runtime warnings when entering xmon.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Entering xmon
BUG: using smp_processor_id() in preemptible [] code: khvcd/280
caller is .xmon_core+0xb8/0x8ec
Call Trace:
[CFD737C0] [C000FAAC] .show_stack+0x68/0x1b0 (unreliable)
[CFD73860] [C01F71F0] .debug_smp_processor_id+0xc8/0xf8
[CFD738F0] [C004AF30] .xmon_core+0xb8/0x8ec
[CFD73A80] [C004B918] .xmon+0x38/0x4c
[CFD73C60] [C004BA8C] .sysrq_handle_xmon+0x48/0x5c
[CFD73CD0] [C0243A68] .__handle_sysrq+0xe0/0x1b0
[CFD73D70] [C0244974] .hvc_poll+0x18c/0x2b4
[CFD73E50] [C0244E80] .khvcd+0x88/0x164
[CFD73EE0] [C0075014] .kthread+0x124/0x174
[CFD73F90] [C0023D48] .kernel_thread+0x4c/0x68
BUG: khvcd:280 task might have lost a preemption check!
Call Trace:
[CFD73740] [C000FAAC] .show_stack+0x68/0x1b0 (unreliable)
[CFD737E0] [C0054920] .preempt_enable_no_resched+0x64/0x7c
[CFD73860] [C01F71F8] .debug_smp_processor_id+0xd0/0xf8
[CFD738F0] [C004AF30] .xmon_core+0xb8/0x8ec
[CFD73A80] [C004B918] .xmon+0x38/0x4c
[CFD73C60] [C004BA8C] .sysrq_handle_xmon+0x48/0x5c
[CFD73CD0] [C0243A68] .__handle_sysrq+0xe0/0x1b0
[CFD73D70] [C0244974] .hvc_poll+0x18c/0x2b4
[CFD73E50] [C0244E80] .khvcd+0x88/0x164
[CFD73EE0] [C0075014] .kthread+0x124/0x174
[CFD73F90] [C0023D48] .kernel_thread+0x4c/0x68
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
I'd appreciate if experts on xmon would give any comments/suggestions
on this. These warnings was just found yesterday, this patch seems to
eliminate the warnings but I have not looked into it seriously.
Signed-off-by: Tsutomu Owa <[EMAIL PROTECTED]>
-- owa
diff -rup linux-rt8/arch/powerpc/xmon/xmon.c rt/arch/powerpc/xmon/xmon.c
--- linux-rt8/arch/powerpc/xmon/xmon.c 2007-02-20 09:38:52.0 +0900
+++ rt/arch/powerpc/xmon/xmon.c 2007-03-05 15:29:46.0 +0900
@@ -342,6 +342,7 @@ static int xmon_core(struct pt_regs *reg
msr = mfmsr();
mtmsr(msr & ~MSR_EE); /* disable interrupts */
+ preempt_disable();
bp = in_breakpoint_table(regs->nip, &offset);
if (bp != NULL) {
@@ -516,6 +517,7 @@ static int xmon_core(struct pt_regs *reg
insert_cpu_bpts();
+ preempt_enable();
mtmsr(msr); /* restore interrupt enable */
return cmd != 'X' && cmd != EOF;
-
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