4 files changed, 57 insertions, 19 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e8327686d3c5..e330da21b84f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -21,7 +21,7 @@ config X86
         select HAVE_UNSTABLE_SCHED_CLOCK
         select HAVE_IDE
         select HAVE_OPROFILE
-        select HAVE_PERF_EVENTS if (!M386 && !M486)
+        select HAVE_PERF_EVENTS
         select HAVE_IRQ_WORK
         select HAVE_IOREMAP_PROT
         select HAVE_KPROBES
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index ed6310183efb..6d75b9145b13 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -381,6 +381,20 @@ static void release_pmc_hardware(void) {}
 
 #endif
 
+static bool check_hw_exists(void)
+{
+        u64 val, val_new = 0;
+        int ret = 0;
+
+        val = 0xabcdUL;
+        ret |= checking_wrmsrl(x86_pmu.perfctr, val);
+        ret |= rdmsrl_safe(x86_pmu.perfctr, &val_new);
+        if (ret || val != val_new)
+                return false;
+
+        return true;
+}
+
 static void reserve_ds_buffers(void);
 static void release_ds_buffers(void);
 
@@ -1372,6 +1386,12 @@ void __init init_hw_perf_events(void)
 
         pmu_check_apic();
 
+        /* sanity check that the hardware exists or is emulated */
+        if (!check_hw_exists()) {
+                pr_cont("Broken PMU hardware detected, software events only.\n");
+                return;
+        }
+
         pr_cont("%s PMU driver.\n", x86_pmu.name);
 
         if (x86_pmu.quirks)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 40150f345982..de2c41758e29 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -850,6 +850,7 @@ struct perf_event_context {
         int                             nr_active;
         int                             is_active;
         int                             nr_stat;
+        int                             rotate_disable;
         atomic_t                        refcount;
         struct task_struct              *task;
 
@@ -908,20 +909,6 @@ extern int perf_num_counters(void);
 extern const char *perf_pmu_name(void);
 extern void __perf_event_task_sched_in(struct task_struct *task);
 extern void __perf_event_task_sched_out(struct task_struct *task, struct task_struct *next);
-
-extern atomic_t perf_task_events;
-
-static inline void perf_event_task_sched_in(struct task_struct *task)
-{
-        COND_STMT(&perf_task_events, __perf_event_task_sched_in(task));
-}
-
-static inline
-void perf_event_task_sched_out(struct task_struct *task, struct task_struct *next)
-{
-        COND_STMT(&perf_task_events, __perf_event_task_sched_out(task, next));
-}
-
 extern int perf_event_init_task(struct task_struct *child);
 extern void perf_event_exit_task(struct task_struct *child);
 extern void perf_event_free_task(struct task_struct *task);
@@ -1030,6 +1017,21 @@ have_event:
         __perf_sw_event(event_id, nr, nmi, regs, addr);
 }
 
+extern atomic_t perf_task_events;
+
+static inline void perf_event_task_sched_in(struct task_struct *task)
+{
+        COND_STMT(&perf_task_events, __perf_event_task_sched_in(task));
+}
+
+static inline
+void perf_event_task_sched_out(struct task_struct *task, struct task_struct *next)
+{
+        perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, NULL, 0);
+
+        COND_STMT(&perf_task_events, __perf_event_task_sched_out(task, next));
+}
+
 extern void perf_event_mmap(struct vm_area_struct *vma);
 extern struct perf_guest_info_callbacks *perf_guest_cbs;
 extern int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 671f6c8c8a32..eac7e3364335 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1287,8 +1287,6 @@ void __perf_event_task_sched_out(struct task_struct *task,
 {
         int ctxn;
 
-        perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, NULL, 0);
-
         for_each_task_context_nr(ctxn)
                 perf_event_context_sched_out(task, ctxn, next);
 }
@@ -1622,8 +1620,12 @@ static void rotate_ctx(struct perf_event_context *ctx)
 {
         raw_spin_lock(&ctx->lock);
 
-        /* Rotate the first entry last of non-pinned groups */
-        list_rotate_left(&ctx->flexible_groups);
+        /*
+         * Rotate the first entry last of non-pinned groups. Rotation might be
+         * disabled by the inheritance code.
+         */
+        if (!ctx->rotate_disable)
+                list_rotate_left(&ctx->flexible_groups);
 
         raw_spin_unlock(&ctx->lock);
 }
@@ -6162,6 +6164,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
         struct perf_event *event;
         struct task_struct *parent = current;
         int inherited_all = 1;
+        unsigned long flags;
         int ret = 0;
 
         child->perf_event_ctxp[ctxn] = NULL;
@@ -6202,6 +6205,15 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
                         break;
         }
 
+        /*
+         * We can't hold ctx->lock when iterating the ->flexible_group list due
+         * to allocations, but we need to prevent rotation because
+         * rotate_ctx() will change the list from interrupt context.
+         */
+        raw_spin_lock_irqsave(&parent_ctx->lock, flags);
+        parent_ctx->rotate_disable = 1;
+        raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+
         list_for_each_entry(event, &parent_ctx->flexible_groups, group_entry) {
                 ret = inherit_task_group(event, parent, parent_ctx,
                                          child, ctxn, &inherited_all);
@@ -6209,6 +6221,10 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
                         break;
         }
 
+        raw_spin_lock_irqsave(&parent_ctx->lock, flags);
+        parent_ctx->rotate_disable = 0;
+        raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+
         child_ctx = child->perf_event_ctxp[ctxn];
 
         if (child_ctx && inherited_all) {