Date:   Sat, 29 Oct 2016 17:38:25 -0700
From:   David Carrillo-Cisneros <davidcc@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     "x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vegard Nossum <vegard.nossum@...il.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Nilay Vaish <nilayvaish@...il.com>,
        Borislav Petkov <bp@...e.de>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Paul Turner <pjt@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>
Subject: [PATCH v3 28/46] perf,perf/x86,perf/powerpc,perf/arm,perf/*: add int error return to pmu::read

New PMUs, such as CMT's, do not guarantee that a read will succeed even
if pmu::add was successful.

In the generic code, this patch adds an int error return and completes the
error checking path up to perf_read().

In CMT's PMU, it adds proper error handling of hw read failure errors.
In other PMUs, pmu::read() simply returns 0.

Reviewed-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: David Carrillo-Cisneros <davidcc@...gle.com>
---
 arch/alpha/kernel/perf_event.c           |  3 +-
 arch/arc/kernel/perf_event.c             |  3 +-
 arch/arm64/include/asm/hw_breakpoint.h   |  2 +-
 arch/arm64/kernel/hw_breakpoint.c        |  3 +-
 arch/metag/kernel/perf/perf_event.c      |  5 +--
 arch/mips/kernel/perf_event_mipsxx.c     |  3 +-
 arch/powerpc/include/asm/hw_breakpoint.h |  2 +-
 arch/powerpc/kernel/hw_breakpoint.c      |  3 +-
 arch/powerpc/perf/core-book3s.c          | 11 +++---
 arch/powerpc/perf/core-fsl-emb.c         |  5 +--
 arch/powerpc/perf/hv-24x7.c              |  5 +--
 arch/powerpc/perf/hv-gpci.c              |  3 +-
 arch/s390/kernel/perf_cpum_cf.c          |  5 +--
 arch/s390/kernel/perf_cpum_sf.c          |  3 +-
 arch/sh/include/asm/hw_breakpoint.h      |  2 +-
 arch/sh/kernel/hw_breakpoint.c           |  3 +-
 arch/sparc/kernel/perf_event.c           |  2 +-
 arch/tile/kernel/perf_event.c            |  3 +-
 arch/x86/events/amd/ibs.c                |  2 +-
 arch/x86/events/amd/iommu.c              |  5 +--
 arch/x86/events/amd/uncore.c             |  3 +-
 arch/x86/events/core.c                   |  3 +-
 arch/x86/events/intel/bts.c              |  3 +-
 arch/x86/events/intel/cmt.c              |  4 ++-
 arch/x86/events/intel/cstate.c           |  3 +-
 arch/x86/events/intel/pt.c               |  3 +-
 arch/x86/events/intel/rapl.c             |  3 +-
 arch/x86/events/intel/uncore.c           |  3 +-
 arch/x86/events/intel/uncore.h           |  2 +-
 arch/x86/events/msr.c                    |  3 +-
 arch/x86/include/asm/hw_breakpoint.h     |  2 +-
 arch/x86/kernel/hw_breakpoint.c          |  3 +-
 arch/x86/kvm/pmu.h                       | 10 +++---
 drivers/bus/arm-cci.c                    |  3 +-
 drivers/bus/arm-ccn.c                    |  3 +-
 drivers/perf/arm_pmu.c                   |  3 +-
 include/linux/perf_event.h               |  6 ++--
 kernel/events/core.c                     | 60 ++++++++++++++++++++------------
 38 files changed, 120 insertions(+), 73 deletions(-)

diff --git a/arch/alpha/kernel/perf_event.c b/arch/alpha/kernel/perf_event.c
index 5c218aa..3bf8a60 100644
--- a/arch/alpha/kernel/perf_event.c
+++ b/arch/alpha/kernel/perf_event.c
@@ -520,11 +520,12 @@ static void alpha_pmu_del(struct perf_event *event, int flags)
 }
 
 
-static void alpha_pmu_read(struct perf_event *event)
+static int alpha_pmu_read(struct perf_event *event)
 {
 	struct hw_perf_event *hwc = &event->hw;
 
 	alpha_perf_event_update(event, hwc, hwc->idx, 0);
+	return 0;
 }
 
 
diff --git a/arch/arc/kernel/perf_event.c b/arch/arc/kernel/perf_event.c
index 2ce24e7..efbcc2d 100644
--- a/arch/arc/kernel/perf_event.c
+++ b/arch/arc/kernel/perf_event.c
@@ -116,9 +116,10 @@ static void arc_perf_event_update(struct perf_event *event,
 	local64_sub(delta, &hwc->period_left);
 }
 
-static void arc_pmu_read(struct perf_event *event)
+static int arc_pmu_read(struct perf_event *event)
 {
 	arc_perf_event_update(event, &event->hw, event->hw.idx);
+	return 0;
 }
 
 static int arc_pmu_cache_event(u64 config)
diff --git a/arch/arm64/include/asm/hw_breakpoint.h b/arch/arm64/include/asm/hw_breakpoint.h
index 9510ace..f82f21f 100644
--- a/arch/arm64/include/asm/hw_breakpoint.h
+++ b/arch/arm64/include/asm/hw_breakpoint.h
@@ -127,7 +127,7 @@ extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
 
 extern int arch_install_hw_breakpoint(struct perf_event *bp);
 extern void arch_uninstall_hw_breakpoint(struct perf_event *bp);
-extern void hw_breakpoint_pmu_read(struct perf_event *bp);
+extern int hw_breakpoint_pmu_read(struct perf_event *bp);
 extern int hw_breakpoint_slots(int type);
 
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
index 948b731..a4fe1c5 100644
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -936,8 +936,9 @@ static int __init arch_hw_breakpoint_init(void)
 }
 arch_initcall(arch_hw_breakpoint_init);
 
-void hw_breakpoint_pmu_read(struct perf_event *bp)
+int hw_breakpoint_pmu_read(struct perf_event *bp)
 {
+	return 0;
 }
 
 /*
diff --git a/arch/metag/kernel/perf/perf_event.c b/arch/metag/kernel/perf/perf_event.c
index 052cba2..128aa0a 100644
--- a/arch/metag/kernel/perf/perf_event.c
+++ b/arch/metag/kernel/perf/perf_event.c
@@ -360,15 +360,16 @@ static void metag_pmu_del(struct perf_event *event, int flags)
 	perf_event_update_userpage(event);
 }
 
-static void metag_pmu_read(struct perf_event *event)
+static int metag_pmu_read(struct perf_event *event)
 {
 	struct hw_perf_event *hwc = &event->hw;
 
 	/* Don't read disabled counters! */
 	if (hwc->idx < 0)
-		return;
+		return 0;
 
 	metag_pmu_event_update(event, hwc, hwc->idx);
+	return 0;
 }
 
 static struct pmu pmu = {
diff --git a/arch/mips/kernel/perf_event_mipsxx.c b/arch/mips/kernel/perf_event_mipsxx.c
index d3ba9f4..d64ed3e 100644
--- a/arch/mips/kernel/perf_event_mipsxx.c
+++ b/arch/mips/kernel/perf_event_mipsxx.c
@@ -507,7 +507,7 @@ static void mipspmu_del(struct perf_event *event, int flags)
 	perf_event_update_userpage(event);
 }
 
-static void mipspmu_read(struct perf_event *event)
+static int mipspmu_read(struct perf_event *event)
 {
 	struct hw_perf_event *hwc = &event->hw;
 
@@ -516,6 +516,7 @@ static void mipspmu_read(struct perf_event *event)
 		return;
 
 	mipspmu_event_update(event, hwc, hwc->idx);
+	return 0;
 }
 
 static void mipspmu_enable(struct pmu *pmu)
diff --git a/arch/powerpc/include/asm/hw_breakpoint.h b/arch/powerpc/include/asm/hw_breakpoint.h
index ac6432d..5218696 100644
--- a/arch/powerpc/include/asm/hw_breakpoint.h
+++ b/arch/powerpc/include/asm/hw_breakpoint.h
@@ -66,7 +66,7 @@ extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
 						unsigned long val, void *data);
 int arch_install_hw_breakpoint(struct perf_event *bp);
 void arch_uninstall_hw_breakpoint(struct perf_event *bp);
-void hw_breakpoint_pmu_read(struct perf_event *bp);
+int hw_breakpoint_pmu_read(struct perf_event *bp);
 extern void flush_ptrace_hw_breakpoint(struct task_struct *tsk);
 
 extern struct pmu perf_ops_bp;
diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index 9781c69..8a016ad 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -364,7 +364,8 @@ void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 	t->ptrace_bps[0] = NULL;
 }
 
-void hw_breakpoint_pmu_read(struct perf_event *bp)
+int hw_breakpoint_pmu_read(struct perf_event *bp)
 {
 	/* TODO */
+	return 0;
 }
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 72c27b8..1019d1e 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1002,20 +1002,20 @@ static u64 check_and_compute_delta(u64 prev, u64 val)
 	return delta;
 }
 
-static void power_pmu_read(struct perf_event *event)
+static int power_pmu_read(struct perf_event *event)
 {
 	s64 val, delta, prev;
 
 	if (event->hw.state & PERF_HES_STOPPED)
-		return;
+		return 0;
 
 	if (!event->hw.idx)
-		return;
+		return 0;
 
 	if (is_ebb_event(event)) {
 		val = read_pmc(event->hw.idx);
 		local64_set(&event->hw.prev_count, val);
-		return;
+		return 0;
 	}
 
 	/*
@@ -1029,7 +1029,7 @@ static void power_pmu_read(struct perf_event *event)
 		val = read_pmc(event->hw.idx);
 		delta = check_and_compute_delta(prev, val);
 		if (!delta)
-			return;
+			return 0;
 	} while (local64_cmpxchg(&event->hw.prev_count, prev, val) != prev);
 
 	local64_add(delta, &event->count);
@@ -1049,6 +1049,7 @@ static void power_pmu_read(struct perf_event *event)
 		if (val < 1)
 			val = 1;
 	} while (local64_cmpxchg(&event->hw.period_left, prev, val) != prev);
+	return 0;
 }
 
 /*
diff --git a/arch/powerpc/perf/core-fsl-emb.c b/arch/powerpc/perf/core-fsl-emb.c
index 5d747b4..46d982e 100644
--- a/arch/powerpc/perf/core-fsl-emb.c
+++ b/arch/powerpc/perf/core-fsl-emb.c
@@ -176,12 +176,12 @@ static void write_pmlcb(int idx, unsigned long val)
 	isync();
 }
 
-static void fsl_emb_pmu_read(struct perf_event *event)
+static int fsl_emb_pmu_read(struct perf_event *event)
 {
 	s64 val, delta, prev;
 
 	if (event->hw.state & PERF_HES_STOPPED)
-		return;
+		return 0;
 
 	/*
 	 * Performance monitor interrupts come even when interrupts
@@ -198,6 +198,7 @@ static void fsl_emb_pmu_read(struct perf_event *event)
 	delta = (val - prev) & 0xfffffffful;
 	local64_add(delta, &event->count);
 	local64_sub(delta, &event->hw.period_left);
+	return 0;
 }
 
 /*
diff --git a/arch/powerpc/perf/hv-24x7.c b/arch/powerpc/perf/hv-24x7.c
index 7b2ca16..41cd973 100644
--- a/arch/powerpc/perf/hv-24x7.c
+++ b/arch/powerpc/perf/hv-24x7.c
@@ -1268,7 +1268,7 @@ static void update_event_count(struct perf_event *event, u64 now)
 	local64_add(now - prev, &event->count);
 }
 
-static void h_24x7_event_read(struct perf_event *event)
+static int h_24x7_event_read(struct perf_event *event)
 {
 	u64 now;
 	struct hv_24x7_request_buffer *request_buffer;
@@ -1289,7 +1289,7 @@ static void h_24x7_event_read(struct perf_event *event)
 		int ret;
 
 		if (__this_cpu_read(hv_24x7_txn_err))
-			return;
+			return 0;
 
 		request_buffer = (void *)get_cpu_var(hv_24x7_reqb);
 
@@ -1323,6 +1323,7 @@ static void h_24x7_event_read(struct perf_event *event)
 		now = h_24x7_get_value(event);
 		update_event_count(event, now);
 	}
+	return 0;
 }
 
 static void h_24x7_event_start(struct perf_event *event, int flags)
diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
index 43fabb3..66c1ce7 100644
--- a/arch/powerpc/perf/hv-gpci.c
+++ b/arch/powerpc/perf/hv-gpci.c
@@ -191,12 +191,13 @@ static u64 h_gpci_get_value(struct perf_event *event)
 	return count;
 }
 
-static void h_gpci_event_update(struct perf_event *event)
+static int h_gpci_event_update(struct perf_event *event)
 {
 	s64 prev;
 	u64 now = h_gpci_get_value(event);
 	prev = local64_xchg(&event->hw.prev_count, now);
 	local64_add(now - prev, &event->count);
+	return 0;
 }
 
 static void h_gpci_event_start(struct perf_event *event, int flags)
diff --git a/arch/s390/kernel/perf_cpum_cf.c b/arch/s390/kernel/perf_cpum_cf.c
index 037c2a2..37fa78c 100644
--- a/arch/s390/kernel/perf_cpum_cf.c
+++ b/arch/s390/kernel/perf_cpum_cf.c
@@ -471,12 +471,13 @@ static int hw_perf_event_update(struct perf_event *event)
 	return err;
 }
 
-static void cpumf_pmu_read(struct perf_event *event)
+static int cpumf_pmu_read(struct perf_event *event)
 {
 	if (event->hw.state & PERF_HES_STOPPED)
-		return;
+		return 0;
 
 	hw_perf_event_update(event);
+	return 0;
 }
 
 static void cpumf_pmu_start(struct perf_event *event, int flags)
diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c
index fcc634c..87fd04a 100644
--- a/arch/s390/kernel/perf_cpum_sf.c
+++ b/arch/s390/kernel/perf_cpum_sf.c
@@ -1296,9 +1296,10 @@ static void hw_perf_event_update(struct perf_event *event, int flush_all)
 				    sampl_overflow, event_overflow);
 }
 
-static void cpumsf_pmu_read(struct perf_event *event)
+static int cpumsf_pmu_read(struct perf_event *event)
 {
 	/* Nothing to do ... updates are interrupt-driven */
+	return 0;
 }
 
 /* Activate sampling control.
diff --git a/arch/sh/include/asm/hw_breakpoint.h b/arch/sh/include/asm/hw_breakpoint.h
index ec9ad59..d3ad1bf 100644
--- a/arch/sh/include/asm/hw_breakpoint.h
+++ b/arch/sh/include/asm/hw_breakpoint.h
@@ -60,7 +60,7 @@ extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
 
 int arch_install_hw_breakpoint(struct perf_event *bp);
 void arch_uninstall_hw_breakpoint(struct perf_event *bp);
-void hw_breakpoint_pmu_read(struct perf_event *bp);
+int hw_breakpoint_pmu_read(struct perf_event *bp);
 
 extern void arch_fill_perf_breakpoint(struct perf_event *bp);
 extern int register_sh_ubc(struct sh_ubc *);
diff --git a/arch/sh/kernel/hw_breakpoint.c b/arch/sh/kernel/hw_breakpoint.c
index 2197fc5..3a2e719 100644
--- a/arch/sh/kernel/hw_breakpoint.c
+++ b/arch/sh/kernel/hw_breakpoint.c
@@ -401,9 +401,10 @@ int __kprobes hw_breakpoint_exceptions_notify(struct notifier_block *unused,
 	return hw_breakpoint_handler(data);
 }
 
-void hw_breakpoint_pmu_read(struct perf_event *bp)
+int hw_breakpoint_pmu_read(struct perf_event *bp)
 {
 	/* TODO */
+	return 0;
 }
 
 int register_sh_ubc(struct sh_ubc *ubc)
diff --git a/arch/sparc/kernel/perf_event.c b/arch/sparc/kernel/perf_event.c
index 710f327..ab118e9 100644
--- a/arch/sparc/kernel/perf_event.c
+++ b/arch/sparc/kernel/perf_event.c
@@ -1131,7 +1131,7 @@ static void sparc_pmu_del(struct perf_event *event, int _flags)
 	local_irq_restore(flags);
 }
 
-static void sparc_pmu_read(struct perf_event *event)
+static int sparc_pmu_read(struct perf_event *event)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 	int idx = active_event_index(cpuc, event);
diff --git a/arch/tile/kernel/perf_event.c b/arch/tile/kernel/perf_event.c
index 6394c1c..e18cdf2 100644
--- a/arch/tile/kernel/perf_event.c
+++ b/arch/tile/kernel/perf_event.c
@@ -734,9 +734,10 @@ static void tile_pmu_del(struct perf_event *event, int flags)
 /*
  * Propagate event elapsed time into the event.
  */
-static inline void tile_pmu_read(struct perf_event *event)
+static inline int tile_pmu_read(struct perf_event *event)
 {
 	tile_perf_event_update(event);
+	return 0;
 }
 
 /*
diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index b26ee32..3de2ada 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -511,7 +511,7 @@ static void perf_ibs_del(struct perf_event *event, int flags)
 	perf_event_update_userpage(event);
 }
 
-static void perf_ibs_read(struct perf_event *event) { }
+static int perf_ibs_read(struct perf_event *event) { return 0; }
 
 PMU_FORMAT_ATTR(rand_en,	"config:57");
 PMU_FORMAT_ATTR(cnt_ctl,	"config:19");
diff --git a/arch/x86/events/amd/iommu.c b/arch/x86/events/amd/iommu.c
index b28200d..2bfcaaa 100644
--- a/arch/x86/events/amd/iommu.c
+++ b/arch/x86/events/amd/iommu.c
@@ -317,7 +317,7 @@ static void perf_iommu_start(struct perf_event *event, int flags)
 
 }
 
-static void perf_iommu_read(struct perf_event *event)
+static int perf_iommu_read(struct perf_event *event)
 {
 	u64 count = 0ULL;
 	u64 prev_raw_count = 0ULL;
@@ -335,13 +335,14 @@ static void perf_iommu_read(struct perf_event *event)
 	prev_raw_count =  local64_read(&hwc->prev_count);
 	if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
 					count) != prev_raw_count)
-		return;
+		return 0;
 
 	/* Handling 48-bit counter overflowing */
 	delta = (count << COUNTER_SHIFT) - (prev_raw_count << COUNTER_SHIFT);
 	delta >>= COUNTER_SHIFT;
 	local64_add(delta, &event->count);
 
+	return 0;
 }
 
 static void perf_iommu_stop(struct perf_event *event, int flags)
diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
index 65577f0..c84415d 100644
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -73,7 +73,7 @@ static struct amd_uncore *event_to_amd_uncore(struct perf_event *event)
 	return NULL;
 }
 
-static void amd_uncore_read(struct perf_event *event)
+static int amd_uncore_read(struct perf_event *event)
 {
 	struct hw_perf_event *hwc = &event->hw;
 	u64 prev, new;
@@ -90,6 +90,7 @@ static void amd_uncore_read(struct perf_event *event)
 	delta = (new << COUNTER_SHIFT) - (prev << COUNTER_SHIFT);
 	delta >>= COUNTER_SHIFT;
 	local64_add(delta, &event->count);
+	return 0;
 }
 
 static void amd_uncore_start(struct perf_event *event, int flags)
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index d31735f..9e52a7b 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1848,9 +1848,10 @@ static int __init init_hw_perf_events(void)
 }
 early_initcall(init_hw_perf_events);
 
-static inline void x86_pmu_read(struct perf_event *event)
+static inline int x86_pmu_read(struct perf_event *event)
 {
 	x86_perf_event_update(event);
+	return 0;
 }
 
 /*
diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index 982c9e3..6832d59 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -575,8 +575,9 @@ static int bts_event_init(struct perf_event *event)
 	return 0;
 }
 
-static void bts_event_read(struct perf_event *event)
+static int bts_event_read(struct perf_event *event)
 {
+	return 0;
 }
 
 static __init int bts_init(void)
diff --git a/arch/x86/events/intel/cmt.c b/arch/x86/events/intel/cmt.c
index bd903ae..ef1000f 100644
--- a/arch/x86/events/intel/cmt.c
+++ b/arch/x86/events/intel/cmt.c
@@ -1318,8 +1318,10 @@ static struct monr *monr_next_descendant_post(struct monr *pos,
 	return pos->parent;
 }
 
-static void intel_cmt_event_read(struct perf_event *event)
+static int intel_cmt_event_read(struct perf_event *event)
 {
+	/* To add support in next patches in series */
+	return -ENOTSUPP;
 }
 
 static inline void __intel_cmt_event_start(struct perf_event *event,
diff --git a/arch/x86/events/intel/cstate.c b/arch/x86/events/intel/cstate.c
index 3ca87b5..b96fed8 100644
--- a/arch/x86/events/intel/cstate.c
+++ b/arch/x86/events/intel/cstate.c
@@ -323,7 +323,7 @@ static inline u64 cstate_pmu_read_counter(struct perf_event *event)
 	return val;
 }
 
-static void cstate_pmu_event_update(struct perf_event *event)
+static int cstate_pmu_event_update(struct perf_event *event)
 {
 	struct hw_perf_event *hwc = &event->hw;
 	u64 prev_raw_count, new_raw_count;
@@ -337,6 +337,7 @@ static void cstate_pmu_event_update(struct perf_event *event)
 		goto again;
 
 	local64_add(new_raw_count - prev_raw_count, &event->count);
+	return 0;
 }
 
 static void cstate_pmu_event_start(struct perf_event *event, int mode)
diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index c5047b8..c46f946 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -1356,8 +1356,9 @@ static int pt_event_add(struct perf_event *event, int mode)
 	return ret;
 }
 
-static void pt_event_read(struct perf_event *event)
+static int pt_event_read(struct perf_event *event)
 {
+	return 0;
 }
 
 static void pt_event_destroy(struct perf_event *event)
diff --git a/arch/x86/events/intel/rapl.c b/arch/x86/events/intel/rapl.c
index 0a535ce..37c3dff 100644
--- a/arch/x86/events/intel/rapl.c
+++ b/arch/x86/events/intel/rapl.c
@@ -411,9 +411,10 @@ static int rapl_pmu_event_init(struct perf_event *event)
 	return ret;
 }
 
-static void rapl_pmu_event_read(struct perf_event *event)
+static int rapl_pmu_event_read(struct perf_event *event)
 {
 	rapl_event_update(event);
+	return 0;
 }
 
 static ssize_t rapl_get_attr_cpumask(struct device *dev,
diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c
index efca268..ad7d035 100644
--- a/arch/x86/events/intel/uncore.c
+++ b/arch/x86/events/intel/uncore.c
@@ -580,10 +580,11 @@ static void uncore_pmu_event_del(struct perf_event *event, int flags)
 	event->hw.last_tag = ~0ULL;
 }
 
-void uncore_pmu_event_read(struct perf_event *event)
+int uncore_pmu_event_read(struct perf_event *event)
 {
 	struct intel_uncore_box *box = uncore_event_to_box(event);
 	uncore_perf_event_update(box, event);
+	return 0;
 }
 
 /*
diff --git a/arch/x86/events/intel/uncore.h b/arch/x86/events/intel/uncore.h
index ad986c1..818b0ef 100644
--- a/arch/x86/events/intel/uncore.h
+++ b/arch/x86/events/intel/uncore.h
@@ -345,7 +345,7 @@ struct intel_uncore_box *uncore_pmu_to_box(struct intel_uncore_pmu *pmu, int cpu
 u64 uncore_msr_read_counter(struct intel_uncore_box *box, struct perf_event *event);
 void uncore_pmu_start_hrtimer(struct intel_uncore_box *box);
 void uncore_pmu_cancel_hrtimer(struct intel_uncore_box *box);
-void uncore_pmu_event_read(struct perf_event *event);
+int uncore_pmu_event_read(struct perf_event *event);
 void uncore_perf_event_update(struct intel_uncore_box *box, struct perf_event *event);
 struct event_constraint *
 uncore_get_constraint(struct intel_uncore_box *box, struct perf_event *event);
diff --git a/arch/x86/events/msr.c b/arch/x86/events/msr.c
index 4bb3ec6..add5caf 100644
--- a/arch/x86/events/msr.c
+++ b/arch/x86/events/msr.c
@@ -170,7 +170,7 @@ static inline u64 msr_read_counter(struct perf_event *event)
 
 	return now;
 }
-static void msr_event_update(struct perf_event *event)
+static int msr_event_update(struct perf_event *event)
 {
 	u64 prev, now;
 	s64 delta;
@@ -188,6 +188,7 @@ static void msr_event_update(struct perf_event *event)
 		delta = sign_extend64(delta, 31);
 
 	local64_add(delta, &event->count);
+	return 0;
 }
 
 static void msr_event_start(struct perf_event *event, int flags)
diff --git a/arch/x86/include/asm/hw_breakpoint.h b/arch/x86/include/asm/hw_breakpoint.h
index 6c98be8..a1c4ce00 100644
--- a/arch/x86/include/asm/hw_breakpoint.h
+++ b/arch/x86/include/asm/hw_breakpoint.h
@@ -59,7 +59,7 @@ extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
 
 int arch_install_hw_breakpoint(struct perf_event *bp);
 void arch_uninstall_hw_breakpoint(struct perf_event *bp);
-void hw_breakpoint_pmu_read(struct perf_event *bp);
+int hw_breakpoint_pmu_read(struct perf_event *bp);
 void hw_breakpoint_pmu_unthrottle(struct perf_event *bp);
 
 extern void
diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 8771766..e72ce6e 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -540,7 +540,8 @@ int hw_breakpoint_exceptions_notify(
 	return hw_breakpoint_handler(data);
 }
 
-void hw_breakpoint_pmu_read(struct perf_event *bp)
+int hw_breakpoint_pmu_read(struct perf_event *bp)
 {
 	/* TODO */
+	return 0;
 }
diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index f96e1f9..46fd299 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -39,12 +39,14 @@ static inline u64 pmc_bitmask(struct kvm_pmc *pmc)
 
 static inline u64 pmc_read_counter(struct kvm_pmc *pmc)
 {
-	u64 counter, enabled, running;
+	u64 counter, counter_tmp, enabled, running;
 
 	counter = pmc->counter;
-	if (pmc->perf_event)
-		counter += perf_event_read_value(pmc->perf_event,
-						 &enabled, &running);
+	if (pmc->perf_event) {
+		if (!perf_event_read_value(pmc->perf_event, &counter_tmp,
+					   &enabled, &running))
+			counter += counter_tmp;
+	}
 	/* FIXME: Scaling needed? */
 	return counter & pmc_bitmask(pmc);
 }
diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c
index 8900823..2d27c70 100644
--- a/drivers/bus/arm-cci.c
+++ b/drivers/bus/arm-cci.c
@@ -1033,9 +1033,10 @@ static u64 pmu_event_update(struct perf_event *event)
 	return new_raw_count;
 }
 
-static void pmu_read(struct perf_event *event)
+static int pmu_read(struct perf_event *event)
 {
 	pmu_event_update(event);
+	return 0;
 }
 
 static void pmu_event_set_period(struct perf_event *event)
diff --git a/drivers/bus/arm-ccn.c b/drivers/bus/arm-ccn.c
index d1074d9..846ed8b 100644
--- a/drivers/bus/arm-ccn.c
+++ b/drivers/bus/arm-ccn.c
@@ -1145,9 +1145,10 @@ static void arm_ccn_pmu_event_del(struct perf_event *event, int flags)
 		hrtimer_cancel(&ccn->dt.hrtimer);
 }
 
-static void arm_ccn_pmu_event_read(struct perf_event *event)
+static int arm_ccn_pmu_event_read(struct perf_event *event)
 {
 	arm_ccn_pmu_event_update(event);
+	return 0;
 }
 
 static void arm_ccn_pmu_enable(struct pmu *pmu)
diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index b37b572..aee7dff 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -163,10 +163,11 @@ u64 armpmu_event_update(struct perf_event *event)
 	return new_raw_count;
 }
 
-static void
+static int
 armpmu_read(struct perf_event *event)
 {
 	armpmu_event_update(event);
+	return 0;
 }
 
 static void
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 9f388d4..9120640 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -366,7 +366,7 @@ struct pmu {
 	 * For sampling capable PMUs this will also update the software period
 	 * hw_perf_event::period_left field.
 	 */
-	void (*read)			(struct perf_event *event);
+	int (*read)			(struct perf_event *event);
 
 	/*
 	 * Group events scheduling is treated as a transaction, add
@@ -886,8 +886,8 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr,
 extern void perf_pmu_migrate_context(struct pmu *pmu,
 				int src_cpu, int dst_cpu);
 extern u64 perf_event_read_local(struct perf_event *event);
-extern u64 perf_event_read_value(struct perf_event *event,
-				 u64 *enabled, u64 *running);
+extern int perf_event_read_value(struct perf_event *event,
+				 u64 *total, u64 *enabled, u64 *running);
 
 
 struct perf_sample_data {
diff --git a/kernel/events/core.c b/kernel/events/core.c
index e11a16a..059e5bb 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2721,7 +2721,7 @@ static void __perf_event_sync_stat(struct perf_event *event,
 	 */
 	switch (event->state) {
 	case PERF_EVENT_STATE_ACTIVE:
-		event->pmu->read(event);
+		(void)event->pmu->read(event);
 		/* fall-through */
 
 	case PERF_EVENT_STATE_INACTIVE:
@@ -3473,6 +3473,7 @@ static void __perf_event_read(void *info)
 		return;
 
 	raw_spin_lock(&ctx->lock);
+
 	if (ctx->is_active) {
 		update_context_time(ctx);
 		update_cgrp_time_from_event(event);
@@ -3483,14 +3484,15 @@ static void __perf_event_read(void *info)
 		goto unlock;
 
 	if (!data->group) {
-		pmu->read(event);
-		data->ret = 0;
+		data->ret = pmu->read(event);
 		goto unlock;
 	}
 
 	pmu->start_txn(pmu, PERF_PMU_TXN_READ);
 
-	pmu->read(event);
+	data->ret = pmu->read(event);
+	if (data->ret)
+		goto unlock;
 
 	list_for_each_entry(sub, &event->sibling_list, group_entry) {
 		update_event_times(sub);
@@ -3499,7 +3501,9 @@ static void __perf_event_read(void *info)
 			 * Use sibling's PMU rather than @event's since
 			 * sibling could be on different (eg: software) PMU.
 			 */
-			sub->pmu->read(sub);
+			data->ret = sub->pmu->read(sub);
+			if (data->ret)
+				goto unlock;
 		}
 	}
 
@@ -3520,6 +3524,7 @@ static inline u64 perf_event_count(struct perf_event *event)
  *   - either for the current task, or for this CPU
  *   - does not have inherit set, for inherited task events
  *     will not be local and we cannot read them atomically
+ *   - pmu::read cannot fail
  */
 u64 perf_event_read_local(struct perf_event *event)
 {
@@ -3552,7 +3557,7 @@ u64 perf_event_read_local(struct perf_event *event)
 	 * oncpu == -1).
 	 */
 	if (event->oncpu == smp_processor_id())
-		event->pmu->read(event);
+		(void) event->pmu->read(event);
 
 	val = local64_read(&event->count);
 	local_irq_restore(flags);
@@ -3611,7 +3616,6 @@ static int perf_event_read(struct perf_event *event, bool group)
 			update_event_times(event);
 		raw_spin_unlock_irqrestore(&ctx->lock, flags);
 	}
-
 	return ret;
 }
 
@@ -4219,18 +4223,22 @@ static int perf_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
-u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
+int perf_event_read_value(struct perf_event *event,
+			  u64 *total, u64 *enabled, u64 *running)
 {
 	struct perf_event *child;
-	u64 total = 0;
 
+	int ret;
+	*total = 0;
 	*enabled = 0;
 	*running = 0;
 
 	mutex_lock(&event->child_mutex);
 
-	(void)perf_event_read(event, false);
-	total += perf_event_count(event);
+	ret = perf_event_read(event, false);
+	if (ret)
+		goto exit;
+	*total += perf_event_count(event);
 
 	*enabled += event->total_time_enabled +
 			atomic64_read(&event->child_total_time_enabled);
@@ -4238,14 +4246,17 @@ u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
 			atomic64_read(&event->child_total_time_running);
 
 	list_for_each_entry(child, &event->child_list, child_list) {
-		(void)perf_event_read(child, false);
-		total += perf_event_count(child);
+		ret = perf_event_read(child, false);
+		if (ret)
+			goto exit;
+		*total += perf_event_count(child);
 		*enabled += child->total_time_enabled;
 		*running += child->total_time_running;
 	}
+exit:
 	mutex_unlock(&event->child_mutex);
 
-	return total;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(perf_event_read_value);
 
@@ -4342,9 +4353,11 @@ static int perf_read_one(struct perf_event *event,
 {
 	u64 enabled, running;
 	u64 values[4];
-	int n = 0;
+	int n = 0, ret;
 
-	values[n++] = perf_event_read_value(event, &enabled, &running);
+	ret = perf_event_read_value(event, &values[n++], &enabled, &running);
+	if (ret)
+		return ret;
 	if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
 		values[n++] = enabled;
 	if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
@@ -5625,7 +5638,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
 		values[n++] = running;
 
 	if (leader != event)
-		leader->pmu->read(leader);
+		(void)leader->pmu->read(leader);
 
 	values[n++] = perf_event_count(leader);
 	if (read_format & PERF_FORMAT_ID)
@@ -5638,7 +5651,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
 
 		if ((sub != event) &&
 		    (sub->state == PERF_EVENT_STATE_ACTIVE))
-			sub->pmu->read(sub);
+			(void)sub->pmu->read(sub);
 
 		values[n++] = perf_event_count(sub);
 		if (read_format & PERF_FORMAT_ID)
@@ -7349,8 +7362,9 @@ void __perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)
 	preempt_enable_notrace();
 }
 
-static void perf_swevent_read(struct perf_event *event)
+static int perf_swevent_read(struct perf_event *event)
 {
+	return 0;
 }
 
 static int perf_swevent_add(struct perf_event *event, int flags)
@@ -8263,7 +8277,7 @@ static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer)
 	if (event->state != PERF_EVENT_STATE_ACTIVE)
 		return HRTIMER_NORESTART;
 
-	event->pmu->read(event);
+	(void)event->pmu->read(event);
 
 	perf_sample_data_init(&data, 0, event->hw.last_period);
 	regs = get_irq_regs();
@@ -8378,9 +8392,10 @@ static void cpu_clock_event_del(struct perf_event *event, int flags)
 	cpu_clock_event_stop(event, flags);
 }
 
-static void cpu_clock_event_read(struct perf_event *event)
+static int cpu_clock_event_read(struct perf_event *event)
 {
 	cpu_clock_event_update(event);
+	return 0;
 }
 
 static int cpu_clock_event_init(struct perf_event *event)
@@ -8455,13 +8470,14 @@ static void task_clock_event_del(struct perf_event *event, int flags)
 	task_clock_event_stop(event, PERF_EF_UPDATE);
 }
 
-static void task_clock_event_read(struct perf_event *event)
+static int task_clock_event_read(struct perf_event *event)
 {
 	u64 now = perf_clock();
 	u64 delta = now - event->ctx->timestamp;
 	u64 time = event->ctx->time + delta;
 
 	task_clock_event_update(event, time);
+	return 0;
 }
 
 static int task_clock_event_init(struct perf_event *event)
-- 
2.8.0.rc3.226.g39d4020

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