[PATCH] Convert tlbstate_lock spin_lock to raw_spin_lock

[PATCH] Convert tlbstate_lock spin_lock to raw_spin_lock

[Chirag Jog]

* xavier droubay <xavier.droubay@gmail.com> [2008-09-08 03:06:51]:

> Hello,
> 
> I experienced this "rtmutex.c:743" known bug with rt3 patch, using
> 
>  http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.26.3.tar.bz2
>  http://rt.et.redhat.com/download/patch-2.6.26.3-rt3.bz2
> 
> I compiled this kernel with the "make-kpkg" debian utility.
> 
> I first compiled this kernel with NO SMP, NO HIGHMEM, and partial ACPI
> (without fan, processor, ... modules). Attached file
> "config-2.6.26.3-rt3lowlty.frwr.gz".
> I didn't experience any problem with this kernel.
> 
> I then enabled SMP and HIGHMEM, and experienced  "rtmutex.c:743" BUG.
> Attached files
> "config-2.6.26.3-rt3rt-smp-hm.gz" and  "dmesg.gz" for some BUGGY message.
> 
> 
> I have seen somewhere on the archive, that some people still
> experienced problems with SMP.
> I guess no fix has been done from rt3 to rt7 patch. Can you confirm?
> 
> If so, which recent kernel should I use in order to get smp and rt
> running without problems?
> 
This simple patch should solve the above problem. Seeing the config, its
seems to be a 32bit box.


It convert tlbstate_lock spin_lock to raw_spin_lock.
Preemption has already been disabled, hence this change shouldn't
affect latency numbers.


Signed-Off-By: Chirag <chirag@linux.vnet.ibm.com>


diff --git a/arch/x86/kernel/tlb_32.c b/arch/x86/kernel/tlb_32.c
index 9bb2363..228849c 100644
--- a/arch/x86/kernel/tlb_32.c
+++ b/arch/x86/kernel/tlb_32.c
@@ -23,7 +23,7 @@ DEFINE_PER_CPU(struct tlb_state, cpu_tlbstate)
 static cpumask_t flush_cpumask;
 static struct mm_struct *flush_mm;
 static unsigned long flush_va;
-static DEFINE_SPINLOCK(tlbstate_lock);
+static DEFINE_RAW_SPINLOCK(tlbstate_lock);
 
 /*
  * We cannot call mmdrop() because we are in interrupt context,

Re: [PATCH] Convert tlbstate_lock spin_lock to raw_spin_lock

[Sujit Karataparambil]

Chirag,

  Kindly understand what xavier is trying to do. He is Trying to disable smp.
The RT - Linux Code is dependent on the mutex lock to perform some
soft/hard real time processing. This is an problem with the mutex lock.

Kindly check with some one before signing off patches.

Thanks,
Sujit


On 9/8/08, Chirag Jog <chirag@linux.vnet.ibm.com> wrote:
> * xavier droubay <xavier.droubay@gmail.com> [2008-09-08 03:06:51]:
>
> > Hello,
> >
> > I experienced this "rtmutex.c:743" known bug with rt3 patch, using
> >
> >  http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.26.3.tar.bz2
> >  http://rt.et.redhat.com/download/patch-2.6.26.3-rt3.bz2
> >
> > I compiled this kernel with the "make-kpkg" debian utility.
> >
> > I first compiled this kernel with NO SMP, NO HIGHMEM, and partial ACPI
> > (without fan, processor, ... modules). Attached file
> > "config-2.6.26.3-rt3lowlty.frwr.gz".
> > I didn't experience any problem with this kernel.
> >
> > I then enabled SMP and HIGHMEM, and experienced  "rtmutex.c:743" BUG.
> > Attached files
> > "config-2.6.26.3-rt3rt-smp-hm.gz" and  "dmesg.gz" for some BUGGY message.
> >
> >
> > I have seen somewhere on the archive, that some people still
> > experienced problems with SMP.
> > I guess no fix has been done from rt3 to rt7 patch. Can you confirm?
> >
> > If so, which recent kernel should I use in order to get smp and rt
> > running without problems?
> >
> This simple patch should solve the above problem. Seeing the config, its
> seems to be a 32bit box.
>
>
> It convert tlbstate_lock spin_lock to raw_spin_lock.
> Preemption has already been disabled, hence this change shouldn't
> affect latency numbers.
>
>
> Signed-Off-By: Chirag <chirag@linux.vnet.ibm.com>
>
>
> diff --git a/arch/x86/kernel/tlb_32.c b/arch/x86/kernel/tlb_32.c
> index 9bb2363..228849c 100644
> --- a/arch/x86/kernel/tlb_32.c
> +++ b/arch/x86/kernel/tlb_32.c
> @@ -23,7 +23,7 @@ DEFINE_PER_CPU(struct tlb_state, cpu_tlbstate)
>  static cpumask_t flush_cpumask;
>  static struct mm_struct *flush_mm;
>  static unsigned long flush_va;
> -static DEFINE_SPINLOCK(tlbstate_lock);
> +static DEFINE_RAW_SPINLOCK(tlbstate_lock);
>
>  /*
>  * We cannot call mmdrop() because we are in interrupt context,
>
>
>
> --
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>


-- 
--linux(2.4/2.6),bsd(4.5.x+),solaris(2.5+)

Re: [PATCH] Convert tlbstate_lock spin_lock to raw_spin_lock

[Steven Rostedt]

[ Refrain from using "unlisted-recipients" please! ]


On Mon, 8 Sep 2008, Sujit Karataparambil wrote:

> Chirag,
> 
>   Kindly understand what xavier is trying to do. He is Trying to disable smp.
> The RT - Linux Code is dependent on the mutex lock to perform some
> soft/hard real time processing. This is an problem with the mutex lock.

It is not a problem with the mutex lock.

> 
> Kindly check with some one before signing off patches.

The patch is legit.

The problem is simply that functions like flush_tlb_current_task and 
flush_tlb_mm disable preemption and then call flush_tlb_others.
This function locks the tlbstate_lock which is currently a rtmutex. An 
rtmutex can not be called with preemption disabled. The tlbstate_lock is 
static, small and confined. I'm not sure we can change this code (flushing 
the TLB) in a way where we can allow preemption. This may just be a 
latency that we must hit.

-- Steve