Re: [tip:perf/core] perf/x86: Export some PMU attributes in caps/ directory

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Aug 25, 2017 at 04:55:03AM -0700, tip-bot for Andi Kleen wrote:

> @@ -1798,6 +1808,7 @@ static int __init init_hw_perf_events(void)
>  				   0, x86_pmu.num_counters, 0, 0);
>  
>  	x86_pmu_format_group.attrs = x86_pmu.format_attrs;
> +	x86_pmu_caps_group.attrs = x86_pmu.caps_attrs;
>  
>  	if (x86_pmu.event_attrs)
>  		x86_pmu_events_group.attrs = x86_pmu.event_attrs;
> @@ -2217,6 +2228,7 @@ static const struct attribute_group *x86_pmu_attr_groups[] = {
>  	&x86_pmu_attr_group,
>  	&x86_pmu_format_group,
>  	&x86_pmu_events_group,
> +	&x86_pmu_caps_group,
>  	NULL,
>  };

This generates:

[    1.421821] ------------[ cut here ]------------
[    1.423424] WARNING: CPU: 1 PID: 1 at fs/sysfs/group.c:120 internal_create_group+0x277/0x2c0
[    1.426453] Modules linked in:
[    1.427777] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.13.0-rc7+ #2
[    1.429538] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014
[    1.432218] task: ffff88007c138000 task.stack: ffffc90000008000
[    1.433760] RIP: 0010:internal_create_group+0x277/0x2c0
[    1.435187] RSP: 0018:ffffc9000000bd78 EFLAGS: 00010296
[    1.436757] RAX: 000000000000003b RBX: 0000000000000003 RCX: 0000000000000000
[    1.438461] RDX: 0000000000000001 RSI: ffffffff8109ff63 RDI: ffffffff8109ff63
[    1.447453] RBP: ffffc9000000bdb0 R08: 0000000000000000 R09: 0000000000000102
[    1.449227] R10: ffff88007c0e10d0 R11: 0000000081e22b01 R12: ffffffff81c10fc0
[    1.450924] R13: 0000000000000000 R14: ffff88007b018aa0 R15: ffff88007b018810
[    1.452718] FS:  0000000000000000(0000) GS:ffff88007ec40000(0000) knlGS:0000000000000000
[    1.455053] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.456630] CR2: ffffc900001fc000 CR3: 0000000001c09000 CR4: 00000000000406e0
[    1.458334] Call Trace:
[    1.459341]  sysfs_create_groups+0x41/0x80
[    1.460675]  device_add+0x5ae/0x600
[    1.461842]  ? set_debug_rodata+0x17/0x17
[    1.463042]  pmu_dev_alloc+0x9a/0xf0
[    1.464297]  perf_event_sysfs_init+0x54/0x8d
[    1.465570]  ? trace_event_define_fields_xdp_exception+0x87/0x87
[    1.486645]  do_one_initcall+0x52/0x190
[    1.487872]  ? set_debug_rodata+0x17/0x17
[    1.489188]  kernel_init_freeable+0x11e/0x1a1
[    1.490800]  ? rest_init+0xd0/0xd0
[    1.492628]  kernel_init+0xe/0x100
[    1.494344]  ret_from_fork+0x27/0x40
[    1.496130] Code: 48 83 7a 20 00 0f 85 f5 fd ff ff 48 8b 02 48 8b 37 48 c7 c2 16 d4 9e 81 48 c7 c7 c8 08 9f 81 48 85 c0 48 0f 45 d0 e8 3a 17 ea ff <0f> ff b8 ea ff ff ff e9 ab fe ff ff 48 83 7f 30 00 0f 85 98 fd 
[    1.501991] ---[ end trace aa30ea041c8942a2 ]---

When ran on !intel systems and:

> +static ssize_t max_precise_show(struct device *cdev,
> +				  struct device_attribute *attr,
> +				  char *buf)
> +{
> +	return snprintf(buf, PAGE_SIZE, "%d\n", x86_pmu_max_precise());
> +}
> +
> +static DEVICE_ATTR_RO(max_precise);

is not intel specific at all..

Not very nice.

Boris, could you give this a spin?

---
Subject: perf/x86: Fix caps/ for !Intel

Move the 'max_precise' capability into generic x86 code where it
belongs. This fixes a sysfs splat on !Intel systems where we fail to set
x86_pmu_caps_group.atts.

Fixes: 22688d1c20f5 ("x86/perf: Export some PMU attributes in caps/ directory")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/events/core.c       | 33 ++++++++++++++++++++++++++++-----
 arch/x86/events/intel/core.c | 14 ++------------
 2 files changed, 30 insertions(+), 17 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index d5f98095a155..73a6311c8baa 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1757,10 +1757,7 @@ ssize_t x86_event_sysfs_show(char *page, u64 config, u64 event)
 }
 
 static struct attribute_group x86_pmu_attr_group;
-
-static struct attribute_group x86_pmu_caps_group = {
-	.name = "caps",
-};
+static struct attribute_group x86_pmu_caps_group;
 
 static int __init init_hw_perf_events(void)
 {
@@ -1808,7 +1805,14 @@ static int __init init_hw_perf_events(void)
 				   0, x86_pmu.num_counters, 0, 0);
 
 	x86_pmu_format_group.attrs = x86_pmu.format_attrs;
-	x86_pmu_caps_group.attrs = x86_pmu.caps_attrs;
+
+	if (x86_pmu.caps_attrs) {
+		struct attribute **tmp;
+
+		tmp = merge_attr(x86_pmu_caps_group.attrs, x86_pmu.caps_attrs);
+		if (!WARN_ON(!tmp))
+			x86_pmu_caps_group.attrs = tmp;
+	}
 
 	if (x86_pmu.event_attrs)
 		x86_pmu_events_group.attrs = x86_pmu.event_attrs;
@@ -2224,6 +2228,25 @@ static struct attribute_group x86_pmu_attr_group = {
 	.attrs = x86_pmu_attrs,
 };
 
+static ssize_t max_precise_show(struct device *cdev,
+				  struct device_attribute *attr,
+				  char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%d\n", x86_pmu_max_precise());
+}
+
+static DEVICE_ATTR_RO(max_precise);
+
+static struct attribute *x86_pmu_caps_attrs[] = {
+	&dev_attr_max_precise.attr,
+	NULL
+};
+
+static struct attribute_group x86_pmu_caps_group = {
+	.name = "caps",
+	.attrs = x86_pmu_caps_attrs,
+};
+
 static const struct attribute_group *x86_pmu_attr_groups[] = {
 	&x86_pmu_attr_group,
 	&x86_pmu_format_group,
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 8fa2abd9c8b6..829e89cfcee2 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3820,19 +3820,9 @@ static ssize_t pmu_name_show(struct device *cdev,
 
 static DEVICE_ATTR_RO(pmu_name);
 
-static ssize_t max_precise_show(struct device *cdev,
-				  struct device_attribute *attr,
-				  char *buf)
-{
-	return snprintf(buf, PAGE_SIZE, "%d\n", x86_pmu_max_precise());
-}
-
-static DEVICE_ATTR_RO(max_precise);
-
 static struct attribute *intel_pmu_caps_attrs[] = {
-	&dev_attr_pmu_name.attr,
-	&dev_attr_max_precise.attr,
-	NULL
+       &dev_attr_pmu_name.attr,
+       NULL
 };
 
 static struct attribute *intel_pmu_attrs[] = {