[PATCH v2 0/4] Unify CPU hotplug lock interface

lock_device_hotplug() was recently introduced to serialize CPU & Memory
online/offline and hotplug operations, along with sysfs online interface
restructure (commit 4f3549d7).  With this new locking scheme,
cpu_hotplug_driver_lock() is redundant and is no longer necessary.

This patchset makes sure that lock_device_hotplug() covers all CPU online/
offline interfaces, and then removes cpu_hotplug_driver_lock().

v2:
 - Rebased to the pm tree, bleeding-edge.
 - Changed patch 2/4 to use lock_device_hotplug_sysfs().

---
Toshi Kani (4):
  hotplug, x86: Fix online state in cpu0 debug interface
  hotplug, x86: Add hotplug lock to missing places
  hotplug, x86: Disable ARCH_CPU_PROBE_RELEASE on x86
  hotplug, powerpc, x86: Remove cpu_hotplug_driver_lock()

---
 arch/powerpc/kernel/smp.c              | 12 ----------
 arch/powerpc/platforms/pseries/dlpar.c | 40 +++++++++++++---------------------
 arch/x86/Kconfig                       |  4 ----
 arch/x86/kernel/smpboot.c              | 21 ------------------
 arch/x86/kernel/topology.c             | 11 ++++++----
 drivers/base/cpu.c                     | 34 +++++++++++++++++++----------
 include/linux/cpu.h                    | 13 -----------
 7 files changed, 45 insertions(+), 90 deletions(-)

_debug_hotplug_cpu() is a debug interface that puts cpu0 offline during
boot-up when CONFIG_DEBUG_HOTPLUG_CPU0 is set.  After cpu0 is put offline
in this interface, however, /sys/devices/system/cpu/cpu0/online still
shows 1 (online).

This patch fixes _debug_hotplug_cpu() to update dev->offline when CPU
online/offline operation succeeded.

Signed-off-by: Toshi Kani <redacted>
Acked-by: Rafael J. Wysocki <redacted>
---
 arch/x86/kernel/topology.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index 6e60b5f..5823bbd 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c

@@ -72,16 +72,19 @@ int __ref _debug_hotplug_cpu(int cpu, int action)
 		ret = cpu_down(cpu);
 		if (!ret) {
 			pr_info("CPU %u is now offline\n", cpu);
+			dev->offline = true;
 			kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
 		} else
 			pr_debug("Can't offline CPU%d.\n", cpu);
 		break;
 	case 1:
 		ret = cpu_up(cpu);
-		if (!ret)
+		if (!ret) {
+			dev->offline = false;
 			kobject_uevent(&dev->kobj, KOBJ_ONLINE);
-		else
+		} else {
 			pr_debug("Can't online CPU%d.\n", cpu);
+		}
 		break;
 	default:
 		ret = -EINVAL;

Commit d7c53c9e enabled ARCH_CPU_PROBE_RELEASE on x86 in order to
serialize CPU online/offline operations.  Although it is the config
option to enable CPU hotplug test interfaces, probe & release, it is
also the option to enable cpu_hotplug_driver_lock() as well.  Therefore,
this option had to be enabled on x86 with dummy arch_cpu_probe() and
arch_cpu_release().

Since then, lock_device_hotplug() was introduced to serialize CPU
online/offline & hotplug operations.  Therefore, this config option
is no longer required for the serialization.  This patch disables
this config option on x86 and revert the changes made by commit
d7c53c9e.

Signed-off-by: Toshi Kani <redacted>
Acked-by: Rafael J. Wysocki <redacted>
---
 arch/x86/Kconfig          |    4 ----
 arch/x86/kernel/smpboot.c |   21 ---------------------
 2 files changed, 25 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b32ebf9..c87e49a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig

@@ -255,10 +255,6 @@ config ARCH_HWEIGHT_CFLAGS
 	default "-fcall-saved-ecx -fcall-saved-edx" if X86_32
 	default "-fcall-saved-rdi -fcall-saved-rsi -fcall-saved-rdx -fcall-saved-rcx -fcall-saved-r8 -fcall-saved-r9 -fcall-saved-r10 -fcall-saved-r11" if X86_64
 
-config ARCH_CPU_PROBE_RELEASE
-	def_bool y
-	depends on HOTPLUG_CPU
-
 config ARCH_SUPPORTS_UPROBES
 	def_bool y
 

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index aecc98a..5b24a9d 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c

@@ -82,27 +82,6 @@
 /* State of each CPU */
 DEFINE_PER_CPU(int, cpu_state) = { 0 };
 
-#ifdef CONFIG_HOTPLUG_CPU
-/*
- * We need this for trampoline_base protection from concurrent accesses when
- * off- and onlining cores wildly.
- */
-static DEFINE_MUTEX(x86_cpu_hotplug_driver_mutex);
-
-void cpu_hotplug_driver_lock(void)
-{
-	mutex_lock(&x86_cpu_hotplug_driver_mutex);
-}
-
-void cpu_hotplug_driver_unlock(void)
-{
-	mutex_unlock(&x86_cpu_hotplug_driver_mutex);
-}
-
-ssize_t arch_cpu_probe(const char *buf, size_t count) { return -1; }
-ssize_t arch_cpu_release(const char *buf, size_t count) { return -1; }
-#endif
-
 /* Number of siblings per CPU package */
 int smp_num_siblings = 1;
 EXPORT_SYMBOL(smp_num_siblings);

cpu_hotplug_driver_lock() serializes CPU online/offline operations
when ARCH_CPU_PROBE_RELEASE is set.  This lock interface is no longer
necessary with the following reason:

 - lock_device_hotplug() now protects CPU online/offline operations,
   including the probe & release interfaces enabled by
   ARCH_CPU_PROBE_RELEASE.  The use of cpu_hotplug_driver_lock() is
   redundant.
 - cpu_hotplug_driver_lock() is only valid when ARCH_CPU_PROBE_RELEASE
   is defined, which is misleading and is only enabled on powerpc.

This patch removes the cpu_hotplug_driver_lock() interface.  As
a result, ARCH_CPU_PROBE_RELEASE only enables / disables the cpu
probe & release interface as intended.  There is no functional change
in this patch.

Signed-off-by: Toshi Kani <redacted>
Acked-by: Rafael J. Wysocki <redacted>
Reviewed-by: Nathan Fontenot <redacted>
---
Performed build test only on powerpc.
---
 arch/powerpc/kernel/smp.c              |   12 ----------
 arch/powerpc/platforms/pseries/dlpar.c |   40 ++++++++++++--------------------
 arch/x86/kernel/topology.c             |    2 --
 drivers/base/cpu.c                     |   10 +-------
 include/linux/cpu.h                    |   13 ----------
 5 files changed, 16 insertions(+), 61 deletions(-)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 38b0ba6..1667269 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c

@@ -763,18 +763,6 @@ void __cpu_die(unsigned int cpu)
 		smp_ops->cpu_die(cpu);
 }
 
-static DEFINE_MUTEX(powerpc_cpu_hotplug_driver_mutex);
-
-void cpu_hotplug_driver_lock()
-{
-	mutex_lock(&powerpc_cpu_hotplug_driver_mutex);
-}
-
-void cpu_hotplug_driver_unlock()
-{
-	mutex_unlock(&powerpc_cpu_hotplug_driver_mutex);
-}
-
 void cpu_die(void)
 {
 	if (ppc_md.cpu_die)

diff --git a/arch/powerpc/platforms/pseries/dlpar.c b/arch/powerpc/platforms/pseries/dlpar.c
index a1a7b9a..e39325d 100644
--- a/arch/powerpc/platforms/pseries/dlpar.c
+++ b/arch/powerpc/platforms/pseries/dlpar.c

@@ -387,18 +387,13 @@ static ssize_t dlpar_cpu_probe(const char *buf, size_t count)
 	char *cpu_name;
 	int rc;
 
-	cpu_hotplug_driver_lock();
 	rc = strict_strtoul(buf, 0, &drc_index);
-	if (rc) {
-		rc = -EINVAL;
-		goto out;
-	}
+	if (rc)
+		return -EINVAL;
 
 	dn = dlpar_configure_connector(drc_index);
-	if (!dn) {
-		rc = -EINVAL;
-		goto out;
-	}
+	if (!dn)
+		return -EINVAL;
 
 	/* configure-connector reports cpus as living in the base
 	 * directory of the device tree.  CPUs actually live in the

@@ -407,8 +402,7 @@ static ssize_t dlpar_cpu_probe(const char *buf, size_t count)
 	cpu_name = kasprintf(GFP_KERNEL, "/cpus%s", dn->full_name);
 	if (!cpu_name) {
 		dlpar_free_cc_nodes(dn);
-		rc = -ENOMEM;
-		goto out;
+		return -ENOMEM;
 	}
 
 	kfree(dn->full_name);

@@ -417,22 +411,21 @@ static ssize_t dlpar_cpu_probe(const char *buf, size_t count)
 	rc = dlpar_acquire_drc(drc_index);
 	if (rc) {
 		dlpar_free_cc_nodes(dn);
-		rc = -EINVAL;
-		goto out;
+		return -EINVAL;
 	}
 
 	rc = dlpar_attach_node(dn);
 	if (rc) {
 		dlpar_release_drc(drc_index);
 		dlpar_free_cc_nodes(dn);
-		goto out;
+		return rc;
 	}
 
 	rc = dlpar_online_cpu(dn);
-out:
-	cpu_hotplug_driver_unlock();
+	if (rc)
+		return rc;
 
-	return rc ? rc : count;
+	return count;
 }
 
 static int dlpar_offline_cpu(struct device_node *dn)

@@ -505,30 +498,27 @@ static ssize_t dlpar_cpu_release(const char *buf, size_t count)
 		return -EINVAL;
 	}
 
-	cpu_hotplug_driver_lock();
 	rc = dlpar_offline_cpu(dn);
 	if (rc) {
 		of_node_put(dn);
-		rc = -EINVAL;
-		goto out;
+		return -EINVAL;
 	}
 
 	rc = dlpar_release_drc(*drc_index);
 	if (rc) {
 		of_node_put(dn);
-		goto out;
+		return rc;
 	}
 
 	rc = dlpar_detach_node(dn);
 	if (rc) {
 		dlpar_acquire_drc(*drc_index);
-		goto out;
+		return rc;
 	}
 
 	of_node_put(dn);
-out:
-	cpu_hotplug_driver_unlock();
-	return rc ? rc : count;
+
+	return count;
 }
 
 static int __init pseries_dlpar_init(void)

diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index a3f35eb..649b010 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c

@@ -66,7 +66,6 @@ int __ref _debug_hotplug_cpu(int cpu, int action)
 		return -EINVAL;
 
 	lock_device_hotplug();
-	cpu_hotplug_driver_lock();
 
 	switch (action) {
 	case 0:

@@ -91,7 +90,6 @@ int __ref _debug_hotplug_cpu(int cpu, int action)
 		ret = -EINVAL;
 	}
 
-	cpu_hotplug_driver_unlock();
 	unlock_device_hotplug();
 
 	return ret;

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index dc78e45..9745f03 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c

@@ -46,8 +46,6 @@ static int __ref cpu_subsys_online(struct device *dev)
 	int from_nid, to_nid;
 	int ret;
 
-	cpu_hotplug_driver_lock();
-
 	from_nid = cpu_to_node(cpuid);
 	ret = cpu_up(cpuid);
 	/*

@@ -58,18 +56,12 @@ static int __ref cpu_subsys_online(struct device *dev)
 	if (from_nid != to_nid)
 		change_cpu_under_node(cpu, from_nid, to_nid);
 
-	cpu_hotplug_driver_unlock();
 	return ret;
 }
 
 static int cpu_subsys_offline(struct device *dev)
 {
-	int ret;
-
-	cpu_hotplug_driver_lock();
-	ret = cpu_down(dev->id);
-	cpu_hotplug_driver_unlock();
-	return ret;
+	return cpu_down(dev->id);
 }
 
 void unregister_cpu(struct cpu *cpu)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 801ff9e..3434ef7 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h

@@ -185,19 +185,6 @@ extern void cpu_hotplug_enable(void);
 void clear_tasks_mm_cpumask(int cpu);
 int cpu_down(unsigned int cpu);
 
-#ifdef CONFIG_ARCH_CPU_PROBE_RELEASE
-extern void cpu_hotplug_driver_lock(void);
-extern void cpu_hotplug_driver_unlock(void);
-#else
-static inline void cpu_hotplug_driver_lock(void)
-{
-}
-
-static inline void cpu_hotplug_driver_unlock(void)
-{
-}
-#endif
-
 #else		/* CONFIG_HOTPLUG_CPU */
 
 static inline void cpu_hotplug_begin(void) {}

lock_device_hotplug[_sysfs]() serializes CPU & Memory online/offline
and hotplug operations.  However, this lock is not held in the debug
interfaces below that initiate CPU online/offline operations.

 - _debug_hotplug_cpu(), cpu0 hotplug test interface enabled by
   CONFIG_DEBUG_HOTPLUG_CPU0.
 - cpu_probe_store() and cpu_release_store(), cpu hotplug test interface
   enabled by CONFIG_ARCH_CPU_PROBE_RELEASE.

This patch changes the above interfaces to hold lock_device_hotplug().

Signed-off-by: Toshi Kani <redacted>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Rafael J. Wysocki <redacted>
---
 arch/x86/kernel/topology.c |    2 ++
 drivers/base/cpu.c         |   24 ++++++++++++++++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index 5823bbd..a3f35eb 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c

@@ -65,6 +65,7 @@ int __ref _debug_hotplug_cpu(int cpu, int action)
 	if (!cpu_is_hotpluggable(cpu))
 		return -EINVAL;
 
+	lock_device_hotplug();
 	cpu_hotplug_driver_lock();
 
 	switch (action) {

@@ -91,6 +92,7 @@ int __ref _debug_hotplug_cpu(int cpu, int action)
 	}
 
 	cpu_hotplug_driver_unlock();
+	unlock_device_hotplug();
 
 	return ret;
 }

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 4cf0717..dc78e45 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c

@@ -89,7 +89,17 @@ static ssize_t cpu_probe_store(struct device *dev,
 			       const char *buf,
 			       size_t count)
 {
-	return arch_cpu_probe(buf, count);
+	ssize_t cnt;
+	int ret;
+
+	ret = lock_device_hotplug_sysfs();
+	if (ret)
+		return ret;
+
+	cnt = arch_cpu_probe(buf, count);
+
+	unlock_device_hotplug();
+	return cnt;
 }
 
 static ssize_t cpu_release_store(struct device *dev,

@@ -97,7 +107,17 @@ static ssize_t cpu_release_store(struct device *dev,
 				 const char *buf,
 				 size_t count)
 {
-	return arch_cpu_release(buf, count);
+	ssize_t cnt;
+	int ret;
+
+	ret = lock_device_hotplug_sysfs();
+	if (ret)
+		return ret;
+
+	cnt = arch_cpu_release(buf, count);
+
+	unlock_device_hotplug();
+	return cnt;
 }
 
 static DEVICE_ATTR(probe, S_IWUSR, NULL, cpu_probe_store);

(2013/08/30 9:22), Toshi Kani wrote:

lock_device_hotplug() was recently introduced to serialize CPU & Memory
online/offline and hotplug operations, along with sysfs online interface
restructure (commit 4f3549d7).  With this new locking scheme,
cpu_hotplug_driver_lock() is redundant and is no longer necessary.

This patchset makes sure that lock_device_hotplug() covers all CPU online/
offline interfaces, and then removes cpu_hotplug_driver_lock().

v2:
  - Rebased to the pm tree, bleeding-edge.
  - Changed patch 2/4 to use lock_device_hotplug_sysfs().

---
Toshi Kani (4):
   hotplug, x86: Fix online state in cpu0 debug interface
   hotplug, x86: Add hotplug lock to missing places
   hotplug, x86: Disable ARCH_CPU_PROBE_RELEASE on x86
   hotplug, powerpc, x86: Remove cpu_hotplug_driver_lock()

---

The patch-set looks good to me.

Acked-by: Yasuaki Ishimatsu <redacted>

Thanks,
Yasuaki Ishimatsu

  arch/powerpc/kernel/smp.c              | 12 ----------
  arch/powerpc/platforms/pseries/dlpar.c | 40 +++++++++++++---------------------
  arch/x86/Kconfig                       |  4 ----
  arch/x86/kernel/smpboot.c              | 21 ------------------
  arch/x86/kernel/topology.c             | 11 ++++++----
  drivers/base/cpu.c                     | 34 +++++++++++++++++++----------
  include/linux/cpu.h                    | 13 -----------
  7 files changed, 45 insertions(+), 90 deletions(-)

On Friday, August 30, 2013 11:44:06 AM Yasuaki Ishimatsu wrote:

(2013/08/30 9:22), Toshi Kani wrote:

quoted

lock_device_hotplug() was recently introduced to serialize CPU & Memory
online/offline and hotplug operations, along with sysfs online interface
restructure (commit 4f3549d7).  With this new locking scheme,
cpu_hotplug_driver_lock() is redundant and is no longer necessary.

This patchset makes sure that lock_device_hotplug() covers all CPU online/
offline interfaces, and then removes cpu_hotplug_driver_lock().

v2:
  - Rebased to the pm tree, bleeding-edge.
  - Changed patch 2/4 to use lock_device_hotplug_sysfs().

---
Toshi Kani (4):
   hotplug, x86: Fix online state in cpu0 debug interface
   hotplug, x86: Add hotplug lock to missing places
   hotplug, x86: Disable ARCH_CPU_PROBE_RELEASE on x86
   hotplug, powerpc, x86: Remove cpu_hotplug_driver_lock()

---

The patch-set looks good to me.

Acked-by: Yasuaki Ishimatsu <redacted>

Thanks!  I'll tentatively queue up this series for 3.12 (for the second
half of the merge window).

Thanks,
Rafael

On Fri, 2013-08-30 at 11:44 +0900, Yasuaki Ishimatsu wrote:

(2013/08/30 9:22), Toshi Kani wrote:

quoted

lock_device_hotplug() was recently introduced to serialize CPU & Memory
online/offline and hotplug operations, along with sysfs online interface
restructure (commit 4f3549d7).  With this new locking scheme,
cpu_hotplug_driver_lock() is redundant and is no longer necessary.

This patchset makes sure that lock_device_hotplug() covers all CPU online/
offline interfaces, and then removes cpu_hotplug_driver_lock().

v2:
  - Rebased to the pm tree, bleeding-edge.
  - Changed patch 2/4 to use lock_device_hotplug_sysfs().

---
Toshi Kani (4):
   hotplug, x86: Fix online state in cpu0 debug interface
   hotplug, x86: Add hotplug lock to missing places
   hotplug, x86: Disable ARCH_CPU_PROBE_RELEASE on x86
   hotplug, powerpc, x86: Remove cpu_hotplug_driver_lock()

---

The patch-set looks good to me.

Acked-by: Yasuaki Ishimatsu <redacted>

Thanks Yasuaki!
-Toshi

On Fri, 2013-08-30 at 14:14 +0200, Rafael J. Wysocki wrote:

On Friday, August 30, 2013 11:44:06 AM Yasuaki Ishimatsu wrote:

quoted

(2013/08/30 9:22), Toshi Kani wrote:

quoted

lock_device_hotplug() was recently introduced to serialize CPU & Memory
online/offline and hotplug operations, along with sysfs online interface
restructure (commit 4f3549d7).  With this new locking scheme,
cpu_hotplug_driver_lock() is redundant and is no longer necessary.

This patchset makes sure that lock_device_hotplug() covers all CPU online/
offline interfaces, and then removes cpu_hotplug_driver_lock().

v2:
  - Rebased to the pm tree, bleeding-edge.
  - Changed patch 2/4 to use lock_device_hotplug_sysfs().

---
Toshi Kani (4):
   hotplug, x86: Fix online state in cpu0 debug interface
   hotplug, x86: Add hotplug lock to missing places
   hotplug, x86: Disable ARCH_CPU_PROBE_RELEASE on x86
   hotplug, powerpc, x86: Remove cpu_hotplug_driver_lock()

---

The patch-set looks good to me.

Acked-by: Yasuaki Ishimatsu <redacted>

Thanks!  I'll tentatively queue up this series for 3.12 (for the second
half of the merge window).

Thanks Rafael!
-Toshi

Hi Peter,

Any objections here?

On Thursday, August 29, 2013 06:22:06 PM Toshi Kani wrote:

4 more quoted lines

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

Hi,

On Thursday, August 29, 2013 06:22:09 PM Toshi Kani wrote:

cpu_hotplug_driver_lock() serializes CPU online/offline operations
when ARCH_CPU_PROBE_RELEASE is set.  This lock interface is no longer
necessary with the following reason:

 - lock_device_hotplug() now protects CPU online/offline operations,
   including the probe & release interfaces enabled by
   ARCH_CPU_PROBE_RELEASE.  The use of cpu_hotplug_driver_lock() is
   redundant.
 - cpu_hotplug_driver_lock() is only valid when ARCH_CPU_PROBE_RELEASE
   is defined, which is misleading and is only enabled on powerpc.

This patch removes the cpu_hotplug_driver_lock() interface.  As
a result, ARCH_CPU_PROBE_RELEASE only enables / disables the cpu
probe & release interface as intended.  There is no functional change
in this patch.

Signed-off-by: Toshi Kani <redacted>
Acked-by: Rafael J. Wysocki <redacted>
Reviewed-by: Nathan Fontenot <redacted>

Can you please rebase this patch on top of 3.12-rc2?  It doesn't apply for
me any more.

Thanks,
Rafael

175 more quoted lines

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

On Wed, 2013-09-25 at 08:27 +0000, Rafael J. Wysocki wrote:

Hi,

On Thursday, August 29, 2013 06:22:09 PM Toshi Kani wrote:

quoted

cpu_hotplug_driver_lock() serializes CPU online/offline operations
when ARCH_CPU_PROBE_RELEASE is set.  This lock interface is no longer
necessary with the following reason:

 - lock_device_hotplug() now protects CPU online/offline operations,
   including the probe & release interfaces enabled by
   ARCH_CPU_PROBE_RELEASE.  The use of cpu_hotplug_driver_lock() is
   redundant.
 - cpu_hotplug_driver_lock() is only valid when ARCH_CPU_PROBE_RELEASE
   is defined, which is misleading and is only enabled on powerpc.

This patch removes the cpu_hotplug_driver_lock() interface.  As
a result, ARCH_CPU_PROBE_RELEASE only enables / disables the cpu
probe & release interface as intended.  There is no functional change
in this patch.

Signed-off-by: Toshi Kani <redacted>
Acked-by: Rafael J. Wysocki <redacted>
Reviewed-by: Nathan Fontenot <redacted>

Can you please rebase this patch on top of 3.12-rc2?  It doesn't apply for
me any more.

Yes, I will send this patch on top of 3.12-rc2.

Thanks,
-Toshi