Re: [tip:x86/urgent] x86, CMCI: Add proper detection of end of CMCI storms

Re: [tip:x86/urgent] x86, CMCI: Add proper detection of end of CMCI storms

[William Dauchy]

On Wed, Apr 2, 2014 at 9:55 AM, tip-bot for Chen, Gong <tipbot@zytor.com> wrote:
> Commit-ID:  27f6c573e0f77f7d1cc907c1494c99a61e48b7d8
> Gitweb:     http://git.kernel.org/tip/27f6c573e0f77f7d1cc907c1494c99a61e48b7d8
> Author:     Chen, Gong <gong.chen@linux.intel.com>
> AuthorDate: Thu, 27 Mar 2014 21:24:36 -0400
> Committer:  Tony Luck <tony.luck@intel.com>
> CommitDate: Fri, 28 Mar 2014 13:40:16 -0700
>
> x86, CMCI: Add proper detection of end of CMCI storms
>
> When CMCI storm persists for a long time(at least beyond predefined
> threshold. It's 30 seconds for now), we can watch CMCI storm is
> detected immediately after it subsides.
>
> ...
> Dec 10 22:04:29 kernel: CMCI storm detected: switching to poll mode
> Dec 10 22:04:59 kernel: CMCI storm subsided: switching to interrupt mode
> Dec 10 22:04:59 kernel: CMCI storm detected: switching to poll mode
> Dec 10 22:05:29 kernel: CMCI storm subsided: switching to interrupt mode
> ...
>
> The problem is that our logic that determines that the storm has
> ended is incorrect. We announce the end, re-enable interrupts and
> realize that the storm is still going on, so we switch back to
> polling mode. Rinse, repeat.
>
> When a storm happens we disable signaling of errors via CMCI and begin
> polling machine check banks instead. If we find any logged errors,
> then we need to set a per-cpu flag so that our per-cpu tests that
> check whether the storm is ongoing will see that errors are still
> being logged independently of whether mce_notify_irq() says that the
> error has been fully processed.
>
> cmci_clear() is not the right tool to disable a bank. It disables the
> interrupt for the bank as desired, but it also clears the bit for
> this bank in "mce_banks_owned" so we will skip the bank when polling
> (so we fail to see that the storm continues because we stop looking).
> New cmci_storm_disable_banks() just disables the interrupt while
> allowing polling to continue.
>
> Reported-by: William Dauchy <wdauchy@gmail.com>

Could you use the following address instead?
Reported-by: William Dauchy <william@gandi.net>

Thanks,

> Signed-off-by: Chen, Gong <gong.chen@linux.intel.com>
> Signed-off-by: Tony Luck <tony.luck@intel.com>

-- 
William

Re: [tip:x86/urgent] x86, CMCI: Add proper detection of end of CMCI storms

[Borislav Petkov]

On Wed, Apr 02, 2014 at 10:51:49AM +0200, William Dauchy wrote:
> Could you use the following address instead?
> Reported-by: William Dauchy <william@gandi.net>

It is too late for that now as the patch is in -tip already... Unless
Ingo can still amend it, that is.

But, we're working on a real solution for the storm issue and there
we'll be asking you to test stuff anyway so we'll make sure to use this
mail address then, ok?

:-)

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--

Re: [tip:x86/urgent] x86, CMCI: Add proper detection of end of CMCI storms

[William Dauchy]

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On Apr02 11:01, Borislav Petkov wrote:
> It is too late for that now as the patch is in -tip already... Unless
> Ingo can still amend it, that is.
> 
> But, we're working on a real solution for the storm issue and there
> we'll be asking you to test stuff anyway so we'll make sure to use this
> mail address then, ok?

ack
-- 
William

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Re: [tip:x86/urgent] x86, CMCI: Add proper detection of end of CMCI storms

[Ingo Molnar]

* Borislav Petkov <bp@alien8.de> wrote:

> On Wed, Apr 02, 2014 at 10:51:49AM +0200, William Dauchy wrote:
> > Could you use the following address instead?
> > Reported-by: William Dauchy <william@gandi.net>
> 
> It is too late for that now as the patch is in -tip already... Unless
> Ingo can still amend it, that is.

There are already patches on top of it, so it's not possible - but 
even if it was the last one, since it got committed by Tony I cannot 
rebase or amend it.

Thanks,

	Ingo

Re: [tip:x86/urgent] x86, CMCI: Add proper detection of end of CMCI storms

[Borislav Petkov]

On Wed, Apr 02, 2014 at 12:46:12PM +0200, Ingo Molnar wrote:
> There are already patches on top of it, so it's not possible - but
> even if it was the last one, since it got committed by Tony I cannot
> rebase or amend it.

Ah right, you pulled it from him, sure.

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--

Re: [tip:x86/urgent] x86, CMCI: Add proper detection of end of CMCI storms

[H. Peter Anvin]

On 04/02/2014 12:55 AM, tip-bot for Chen, Gong wrote:
> @@ -614,6 +618,8 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
>  		if (!(m.status & MCI_STATUS_VAL))
>  			continue;
>  
> +		v = &get_cpu_var(mce_polled_error);
> +		set_bit(0, v);
>  		/*
>  		 * Uncorrected or signalled events are handled by the exception
>  		 * handler when it is enabled, so don't process those here.
> @@ -1278,10 +1284,18 @@ static unsigned long mce_adjust_timer_default(unsigned long interval)
>  static unsigned long (*mce_adjust_timer)(unsigned long interval) =
>  	mce_adjust_timer_default;
>  
> +static int cmc_error_seen(void)
> +{
> +	unsigned long *v = &__get_cpu_var(mce_polled_error);
> +
> +	return test_and_clear_bit(0, v);
> +}
> +

Please use this_cpu_*() whereever possible instead of __get_cpu_var().
Since this is not actually a bitmask this_cpu_xchg() can be used at the end.

In fact, using set_bit() is completely wasteful.

I'll push this onward since it is a bit late, but please submit a
cleanup patch.

	-hpa

[PATCH 1/2] x86, CMCI: Fix a missed put_cpu_var

[Chen, Gong]

This issue is introduced in commit 27f6c573e0. I forget to
execute put_cpu_var operation after get_cpu_var.

Signed-off-by: Chen, Gong <gong.chen@linux.intel.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index eeee23f..26eaf3b 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -620,6 +620,7 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
 
 		v = &get_cpu_var(mce_polled_error);
 		set_bit(0, v);
+		put_cpu_var(mce_polled_error);
 		/*
 		 * Uncorrected or signalled events are handled by the exception
 		 * handler when it is enabled, so don't process those here.
-- 
1.9.0

[PATCH 2/2] x86, MCE: Cleanup macro __get_cpu_var

[Chen, Gong]

According to Peter's suggestion, use this_cpu_* instead of
__get_cpu_var. BTW, remove bitmask ops to avoid unnecessary
overhead.

Signed-off-by: Chen, Gong <gong.chen@linux.intel.com>
Suggested-by: H. Peter Anvin <hpa@zytor.com>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 26eaf3b..a44506e 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -402,7 +402,7 @@ static u64 mce_rdmsrl(u32 msr)
 
 		if (offset < 0)
 			return 0;
-		return *(u64 *)((char *)&__get_cpu_var(injectm) + offset);
+		return *(u64 *)((char *)this_cpu_ptr(&injectm) + offset);
 	}
 
 	if (rdmsrl_safe(msr, &v)) {
@@ -424,7 +424,7 @@ static void mce_wrmsrl(u32 msr, u64 v)
 		int offset = msr_to_offset(msr);
 
 		if (offset >= 0)
-			*(u64 *)((char *)&__get_cpu_var(injectm) + offset) = v;
+			*(u64 *)((char *)this_cpu_ptr(&injectm) + offset) = v;
 		return;
 	}
 	wrmsrl(msr, v);
@@ -480,7 +480,7 @@ static DEFINE_PER_CPU(struct mce_ring, mce_ring);
 /* Runs with CPU affinity in workqueue */
 static int mce_ring_empty(void)
 {
-	struct mce_ring *r = &__get_cpu_var(mce_ring);
+	struct mce_ring *r = this_cpu_ptr(&mce_ring);
 
 	return r->start == r->end;
 }
@@ -492,7 +492,7 @@ static int mce_ring_get(unsigned long *pfn)
 
 	*pfn = 0;
 	get_cpu();
-	r = &__get_cpu_var(mce_ring);
+	r = this_cpu_ptr(&mce_ring);
 	if (r->start == r->end)
 		goto out;
 	*pfn = r->ring[r->start];
@@ -506,7 +506,7 @@ out:
 /* Always runs in MCE context with preempt off */
 static int mce_ring_add(unsigned long pfn)
 {
-	struct mce_ring *r = &__get_cpu_var(mce_ring);
+	struct mce_ring *r = this_cpu_ptr(&mce_ring);
 	unsigned next;
 
 	next = (r->end + 1) % MCE_RING_SIZE;
@@ -528,7 +528,7 @@ int mce_available(struct cpuinfo_x86 *c)
 static void mce_schedule_work(void)
 {
 	if (!mce_ring_empty())
-		schedule_work(&__get_cpu_var(mce_work));
+		schedule_work(this_cpu_ptr(&mce_work));
 }
 
 DEFINE_PER_CPU(struct irq_work, mce_irq_work);
@@ -553,7 +553,7 @@ static void mce_report_event(struct pt_regs *regs)
 		return;
 	}
 
-	irq_work_queue(&__get_cpu_var(mce_irq_work));
+	irq_work_queue(this_cpu_ptr(&mce_irq_work));
 }
 
 /*
@@ -619,7 +619,7 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
 			continue;
 
 		v = &get_cpu_var(mce_polled_error);
-		set_bit(0, v);
+		*v = 1;
 		put_cpu_var(mce_polled_error);
 		/*
 		 * Uncorrected or signalled events are handled by the exception
@@ -1053,7 +1053,7 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 
 	mce_gather_info(&m, regs);
 
-	final = &__get_cpu_var(mces_seen);
+	final = this_cpu_ptr(&mces_seen);
 	*final = m;
 
 	memset(valid_banks, 0, sizeof(valid_banks));
@@ -1287,14 +1287,14 @@ static unsigned long (*mce_adjust_timer)(unsigned long interval) =
 
 static int cmc_error_seen(void)
 {
-	unsigned long *v = &__get_cpu_var(mce_polled_error);
+	unsigned long *v = this_cpu_ptr(&mce_polled_error);
 
-	return test_and_clear_bit(0, v);
+	return this_cpu_xchg(*v, 0);
 }
 
 static void mce_timer_fn(unsigned long data)
 {
-	struct timer_list *t = &__get_cpu_var(mce_timer);
+	struct timer_list *t = this_cpu_ptr(&mce_timer);
 	unsigned long iv;
 	int notify;
 
@@ -1302,7 +1302,7 @@ static void mce_timer_fn(unsigned long data)
 
 	if (mce_available(__this_cpu_ptr(&cpu_info))) {
 		machine_check_poll(MCP_TIMESTAMP,
-				&__get_cpu_var(mce_poll_banks));
+				this_cpu_ptr(&mce_poll_banks));
 		mce_intel_cmci_poll();
 	}
 
@@ -1332,7 +1332,7 @@ static void mce_timer_fn(unsigned long data)
  */
 void mce_timer_kick(unsigned long interval)
 {
-	struct timer_list *t = &__get_cpu_var(mce_timer);
+	struct timer_list *t = this_cpu_ptr(&mce_timer);
 	unsigned long when = jiffies + interval;
 	unsigned long iv = __this_cpu_read(mce_next_interval);
 
@@ -1668,7 +1668,7 @@ static void mce_start_timer(unsigned int cpu, struct timer_list *t)
 
 static void __mcheck_cpu_init_timer(void)
 {
-	struct timer_list *t = &__get_cpu_var(mce_timer);
+	struct timer_list *t = this_cpu_ptr(&mce_timer);
 	unsigned int cpu = smp_processor_id();
 
 	setup_timer(t, mce_timer_fn, cpu);
@@ -1711,8 +1711,8 @@ void mcheck_cpu_init(struct cpuinfo_x86 *c)
 	__mcheck_cpu_init_generic();
 	__mcheck_cpu_init_vendor(c);
 	__mcheck_cpu_init_timer();
-	INIT_WORK(&__get_cpu_var(mce_work), mce_process_work);
-	init_irq_work(&__get_cpu_var(mce_irq_work), &mce_irq_work_cb);
+	INIT_WORK(this_cpu_ptr(&mce_work), mce_process_work);
+	init_irq_work(this_cpu_ptr(&mce_irq_work), &mce_irq_work_cb);
 }
 
 /*
@@ -1964,7 +1964,7 @@ static struct miscdevice mce_chrdev_device = {
 static void __mce_disable_bank(void *arg)
 {
 	int bank = *((int *)arg);
-	__clear_bit(bank, __get_cpu_var(mce_poll_banks));
+	__clear_bit(bank, *this_cpu_ptr(&mce_poll_banks));
 	cmci_disable_bank(bank);
 }
 
-- 
1.9.0

Re: [PATCH 2/2] x86, MCE: Cleanup macro __get_cpu_var

[H. Peter Anvin]

On 04/14/2014 01:39 AM, Chen, Gong wrote:
> @@ -619,7 +619,7 @@ void machine_check_poll(enum mcp_flags flags, mce_banks_t *b)
>  			continue;
>  
>  		v = &get_cpu_var(mce_polled_error);
> -		set_bit(0, v);
> +		*v = 1;
>  		put_cpu_var(mce_polled_error);
>  		/*
>  		 * Uncorrected or signalled events are handled by the exception

The amazing thing is that you managed to miss the one place where you
could actively elide a pointer.

The above should simply be:

	this_cpu_write(mce_polled_error, 1);

	-hpa

Re: [PATCH 2/2] x86, MCE: Cleanup macro __get_cpu_var

[H. Peter Anvin]

On 04/14/2014 01:39 AM, Chen, Gong wrote:
> @@ -1287,14 +1287,14 @@ static unsigned long (*mce_adjust_timer)(unsigned long interval) =
>  
>  static int cmc_error_seen(void)
>  {
> -	unsigned long *v = &__get_cpu_var(mce_polled_error);
> +	unsigned long *v = this_cpu_ptr(&mce_polled_error);
>  
> -	return test_and_clear_bit(0, v);
> +	return this_cpu_xchg(*v, 0);
>  }
>  

Here you produce a pointer and *then* passing it through a this_cpu_
function... this is actively wrong.

It should simply be:

	return this_cpu_xchg(mce_polled_error, 0);

	-hpa

Re: [PATCH 2/2] x86, MCE: Cleanup macro __get_cpu_var

[H. Peter Anvin]

Please read Documentation/this_cpu_ops.txt for reference for how to use
these functions.  However, you want to avoid forming a pointer if you
can; it is relatively expensive to do so.

	-hpa

Re: [PATCH 2/2] x86, MCE: Cleanup macro __get_cpu_var

[Chen, Gong]

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On Mon, Apr 14, 2014 at 09:23:08AM -0700, H. Peter Anvin wrote:
> Please read Documentation/this_cpu_ops.txt for reference for how to use
> these functions.  However, you want to avoid forming a pointer if you
> can; it is relatively expensive to do so.
> 
:-). I just found your comment yesterday so that I was eager to finish it.
I should do more homework as you told and send it again. Thanks very much
for your patience.

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