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Date: Fri, 11 Dec 2015 11:11:48 -0700
From: Mathieu Poirier <mathieu.poirier@...aro.org>
To: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Ingo Molnar <mingo@...hat.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
vince@...ter.net, Stephane Eranian <eranian@...gle.com>,
Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering
On 11 December 2015 at 06:36, Alexander Shishkin
<alexander.shishkin@...ux.intel.com> wrote:
> Many instruction trace pmus out there support address range-based
> filtering, which would, for example, generate trace data only for a
> given range of instruction addresses, which is useful for tracing
> individual functions, modules or libraries.
>
> This patch introduces the interface for userspace to specify these
> filters and for the pmu drivers to apply these filters to hardware
> configuration.
>
> The user interface is an ascii string that is passed via an ioctl
> and specifies (in a way similar to uprobe) address ranges within
> certain object files or within kernel. There is no special treatment
> for kernel modules yet, but it might be a worthy pursuit.
>
> The pmu driver interface basically adds an extra callback to the
> pmu driver structure, which validates the filter configuration proposed
> by the user against what the hardware is actually capable of doing
> and translates it into something that pmu::start can program into
> hardware.
>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> ---
> include/linux/perf_event.h | 40 ++++
> kernel/events/core.c | 576 ++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 613 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index f9828a48f1..4ddbedc100 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -127,6 +127,11 @@ struct hw_perf_event {
> };
> struct { /* itrace */
> int itrace_started;
> + /*
> + * PMU would store hardware filter configuration
> + * here.
> + */
> + void *itrace_filters;
> };
> #ifdef CONFIG_HAVE_HW_BREAKPOINT
> struct { /* breakpoint */
> @@ -388,12 +393,38 @@ struct pmu {
> void (*free_aux) (void *aux); /* optional */
>
> /*
> + * Validate instruction tracing filters: make sure hw supports the
> + * requested configuration and number of filters.
> + *
> + * Configure instruction tracing filters: translate hw-agnostic filter
> + * into hardware configuration in event::hw::itrace_filters
> + */
> + int (*itrace_filter_setup) (struct perf_event *event); /* optional */
> +
> + /*
> * Filter events for PMU-specific reasons.
> */
> int (*filter_match) (struct perf_event *event); /* optional */
> };
>
> /**
> + * Instruction trace (ITRACE) filter
> + */
> +struct perf_itrace_filter {
> + struct list_head entry;
> + struct rcu_head rcu_head;
> + struct inode *inode;
> + struct task_struct *task;
> + unsigned long offset;
> + unsigned long size;
> + unsigned long start;
> + unsigned long end;
> + unsigned int range : 1, /* 1: range, 0: addr */
> + filter : 1, /* 1: filter/start, 0: stop */
> + kernel : 1; /* 1: kernel, 0: object file*/
I've seen a rant on the list before about bit fields like these... Do
we gain anything with having them? I personally avoid them to favour
bool types but that will be for Peter to decide. Given its
importance, I also think this structure could you more documentation.
> +};
> +
> +/**
> * enum perf_event_active_state - the states of a event
> */
> enum perf_event_active_state {
> @@ -559,6 +590,10 @@ struct perf_event {
>
> atomic_t event_limit;
>
> + /* instruction trace filters */
> + struct list_head itrace_filters;
> + struct mutex itrace_filters_mutex;
> +
> void (*destroy)(struct perf_event *);
> struct rcu_head rcu_head;
>
> @@ -1032,6 +1067,11 @@ static inline bool has_aux(struct perf_event *event)
> return event->pmu->setup_aux;
> }
>
> +static inline bool has_itrace_filter(struct perf_event *event)
> +{
> + return event->pmu->itrace_filter_setup;
> +}
> +
> extern int perf_output_begin(struct perf_output_handle *handle,
> struct perf_event *event, unsigned int size);
> extern void perf_output_end(struct perf_output_handle *handle);
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 2bab4af901..28ce173a28 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -44,6 +44,8 @@
> #include <linux/compat.h>
> #include <linux/bpf.h>
> #include <linux/filter.h>
> +#include <linux/namei.h>
> +#include <linux/parser.h>
>
> #include "internal.h"
>
> @@ -2335,6 +2337,59 @@ static int __perf_event_stop(void *info)
> return 0;
> }
>
> +static int __perf_event_itrace_filters_setup(void *info)
> +{
> + struct perf_event *event = info;
> + int ret;
> +
> + if (READ_ONCE(event->state) != PERF_EVENT_STATE_ACTIVE)
> + return -EAGAIN;
> +
> + /* matches smp_wmb() in event_sched_in() */
> + smp_rmb();
> +
> + /*
> + * There is a window with interrupts enabled before we get here,
> + * so we need to check again lest we try to stop another cpu's event.
> + */
> + if (READ_ONCE(event->oncpu) != smp_processor_id())
> + return -EAGAIN;
> +
> + event->pmu->stop(event, PERF_EF_UPDATE);
> + rcu_read_lock();
> + ret = event->pmu->itrace_filter_setup(event);
> + rcu_read_unlock();
> + event->pmu->start(event, PERF_EF_RELOAD);
> +
> + return ret;
> +}
> +
> +static int perf_event_itrace_filters_setup(struct perf_event *event)
> +{
> + int ret;
> +
> + /*
> + * We can't use event_function_call() here, because that would
> + * require ctx::mutex, but one of our callers is called with
> + * mm::mmap_sem down, which would cause an inversion, see bullet
> + * (2) in put_event().
> + */
> + do {
> + if (READ_ONCE(event->state) != PERF_EVENT_STATE_ACTIVE) {
> + ret = event->pmu->itrace_filter_setup(event);
> + break;
> + }
> +
> + /* matches smp_wmb() in event_sched_in() */
> + smp_rmb();
> +
> + ret = cpu_function_call(READ_ONCE(event->oncpu),
> + __perf_event_itrace_filters_setup, event);
> + } while (ret == -EAGAIN);
> +
> + return ret;
> +}
> +
> static int _perf_event_refresh(struct perf_event *event, int refresh)
> {
> /*
> @@ -3663,6 +3718,8 @@ static bool exclusive_event_installable(struct perf_event *event,
> return true;
> }
>
> +static void perf_itrace_filters_clear(struct perf_event *event);
> +
> static void __free_event(struct perf_event *event)
> {
> if (!event->parent) {
> @@ -3671,6 +3728,7 @@ static void __free_event(struct perf_event *event)
> }
>
> perf_event_free_bpf_prog(event);
> + perf_itrace_filters_clear(event);
>
> if (event->destroy)
> event->destroy(event);
> @@ -5907,6 +5965,37 @@ out:
> comm_event->event_id.header.size = size;
> }
>
> +/*
> + * Clear all dynamic object-based filters at exec, they'll have to be
> + * re-instated when/if these objects are mmapped again.
> + */
> +static void perf_itrace_exec(struct perf_event *event, void *data)
> +{
> + struct perf_itrace_filter *filter;
> + unsigned int restart = 0;
> +
> + if (!has_itrace_filter(event))
> + return;
> +
> + rcu_read_lock();
> +
> + list_for_each_entry_rcu(filter, &event->itrace_filters, entry) {
> + if (filter->kernel)
> + continue;
> +
> + filter->start = filter->end = 0;
> + restart++;
> + }
> +
> + rcu_read_unlock();
> +
> + /*
> + * kernel filters, however, will still be valid
> + */
> + if (restart)
> + perf_event_itrace_filters_setup(event);
> +}
> +
> static void perf_event_comm_event(struct perf_comm_event *comm_event)
> {
> char comm[TASK_COMM_LEN];
> @@ -5921,6 +6010,8 @@ static void perf_event_comm_event(struct perf_comm_event *comm_event)
>
> comm_event->event_id.header.size = sizeof(comm_event->event_id) + size;
>
> + if (comm_event->event_id.header.misc == PERF_RECORD_MISC_COMM_EXEC)
> + perf_event_aux(perf_itrace_exec, comm_event, NULL, true);
> perf_event_aux(perf_event_comm_output,
> comm_event,
> NULL, false);
> @@ -6159,6 +6250,77 @@ got_name:
> kfree(buf);
> }
>
> +/*
> + * Whether this @filter depends on a dynamic object which is not loaded
> + * yet or its load addresses are not known.
> + */
> +static bool perf_itrace_filter_needs_mmap(struct perf_itrace_filter *filter)
> +{
> + return filter->filter && !filter->kernel && !filter->end;
> +}
> +
> +/*
> + * Check whether inode and address range match filter criteria.
> + */
> +static bool perf_itrace_filter_match(struct perf_itrace_filter *filter,
> + struct file *file, unsigned long offset,
> + unsigned long size)
> +{
> +
Unneeded white space - I'm suprised checkpatch didn't catch it.
> + if (filter->inode != file->f_inode)
> + return false;
> +
> + if (filter->offset > offset + size)
> + return false;
> +
> + if (filter->offset + filter->size < offset)
> + return false;
> +
> + return true;
> +}
> +
> +/*
> + * Update event's itrace filters
> + */
> +static void perf_itrace_filters_update(struct perf_event *event, void *data)
> +{
> + struct perf_mmap_event *mmap_event = data;
> + unsigned long off = mmap_event->vma->vm_pgoff << PAGE_SHIFT;
> + struct file *file = mmap_event->vma->vm_file;
> + struct perf_itrace_filter *filter;
> + unsigned int restart = 0;
> +
> + if (!has_itrace_filter(event))
> + return;
> +
> + if (!file)
> + return;
> +
> + /* we do not modify the list or sleep, no need for the mutex */
> + rcu_read_lock();
> + list_for_each_entry_rcu(filter, &event->itrace_filters, entry) {
> + if (filter->kernel)
> + continue;
> +
> + if (filter->task->mm != mmap_event->vma->vm_mm)
> + continue;
> +
> + if (!perf_itrace_filter_match(filter, file, off,
> + mmap_event->event_id.len))
> + continue;
> +
> + restart++;
> + filter->start = mmap_event->event_id.start + filter->offset;
> + filter->end = mmap_event->event_id.start + filter->offset +
> + filter->size;
> + }
> + rcu_read_unlock();
> +
> + /* reprogram updated filters into hardware */
> + if (restart)
> + perf_event_itrace_filters_setup(event);
> +}
> +
> void perf_event_mmap(struct vm_area_struct *vma)
> {
> struct perf_mmap_event mmap_event;
> @@ -6190,6 +6352,7 @@ void perf_event_mmap(struct vm_area_struct *vma)
> /* .flags (attr_mmap2 only) */
> };
>
> + perf_event_aux(perf_itrace_filters_update, &mmap_event, NULL, true);
> perf_event_mmap_event(&mmap_event);
> }
>
> @@ -7163,13 +7326,405 @@ void perf_bp_event(struct perf_event *bp, void *data)
> }
> #endif
>
> +/*
> + * Insert an itrace @filter into @event's list of filters.
> + * @filter is used as a template
> + */
> +static int perf_itrace_filter_insert(struct perf_event *event,
> + struct perf_itrace_filter *src,
> + struct task_struct *task)
> +{
> + int node = cpu_to_node(event->cpu == -1 ? 0 : event->cpu);
> + struct perf_itrace_filter *filter;
> +
> + filter = kzalloc_node(sizeof(*filter), GFP_KERNEL, node);
> + if (!filter)
> + return -ENOMEM;
> +
> + filter->inode = src->inode;
> + filter->offset = src->offset;
> + filter->size = src->size;
> + filter->range = src->range;
> + filter->filter = src->filter;
> + filter->kernel = src->kernel;
> + /*
> + * We copy the actual address range too: it will remain the same for
> + * kernel addresses and user addresses after fork(); in case of exec
> + * or mmap, it will get cleared or modified by
> + * perf_itrace_filters_clear()/perf_itrace_filters_update().
> + */
> + filter->start = src->start;
> + filter->end = src->end;
> +
> + /*
> + * We're already holding a reference to this task_struct since
> + * alloc_perf_context() till last put_ctx() in __free_event().
> + */
> + filter->task = task;
> +
> + /*
> + * If we're called through perf_itrace_filters_clone(), we're already
> + * holding parent's filter mutex.
> + */
> + mutex_lock_nested(&event->itrace_filters_mutex, SINGLE_DEPTH_NESTING);
> + list_add_tail_rcu(&filter->entry, &event->itrace_filters);
> + mutex_unlock(&event->itrace_filters_mutex);
> +
> + return 0;
> +}
> +
> +static void perf_itrace_filter_free_rcu(struct rcu_head *rcu_head)
> +{
> + struct perf_itrace_filter *filter =
> + container_of(rcu_head, struct perf_itrace_filter, rcu_head);
> +
> + if (filter->inode)
> + iput(filter->inode);
> + kfree(filter);
> +}
> +
> +/*
> + * we can do this via task_function_call(), as well as setting filters
> + * and maybe event updating them!
> + */
> +static void perf_itrace_filters_clear(struct perf_event *event)
> +{
> + struct perf_itrace_filter *filter, *iter;
> +
> + if (!has_itrace_filter(event))
> + return;
> +
> + mutex_lock(&event->itrace_filters_mutex);
> + list_for_each_entry_safe(filter, iter, &event->itrace_filters, entry) {
> + list_del_rcu(&filter->entry);
> + call_rcu(&filter->rcu_head, perf_itrace_filter_free_rcu);
> + }
> +
> + perf_event_itrace_filters_setup(event);
> + mutex_unlock(&event->itrace_filters_mutex);
> +}
> +
> +/*
> + * Scan through mm's vmas and see if one of them matches the
> + * @filter; if so, adjust filter's address range.
> + * Called with mm::mmap_sem down for reading.
> + */
> +static int perf_itrace_filter_apply(struct perf_event *event,
> + struct perf_itrace_filter *filter,
> + struct mm_struct *mm)
> +{
> + struct vm_area_struct *vma;
> +
> + for (vma = mm->mmap; vma->vm_next; vma = vma->vm_next) {
> + struct file *file = vma->vm_file;
> + unsigned long off = vma->vm_pgoff << PAGE_SHIFT;
> + unsigned long vma_size = vma->vm_end - vma->vm_start;
> +
> + if (!file)
> + continue;
> +
> + if (!perf_itrace_filter_match(filter, file, off,
> + vma_size))
> + continue;
> +
> + filter->start = vma->vm_start + filter->offset;
> + filter->end = vma->vm_start + filter->offset +
> + filter->size;
> +
> + return 1;
> + }
> +
> + return 0;
> +}
> +
> +/*
> + * Adjust event's itrace filters' address ranges based on the
> + * task's existing mappings
> + */
> +static void perf_itrace_filters_apply(struct perf_event *event)
> +{
> + struct perf_itrace_filter *filter;
> + struct mm_struct *mm = NULL;
> + unsigned int restart = 0;
> +
> + lockdep_assert_held(&event->ctx->mutex);
> +
> + mm = get_task_mm(event->ctx->task);
> + if (!mm)
> + return;
> +
> + down_read(&mm->mmap_sem);
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(filter, &event->itrace_filters, entry) {
> + if (!perf_itrace_filter_needs_mmap(filter))
> + continue;
> +
> + restart += perf_itrace_filter_apply(event, filter, mm);
> + }
> + rcu_read_unlock();
> +
> + up_read(&mm->mmap_sem);
> +
> + if (restart)
> + perf_event_itrace_filters_setup(event);
> +
> + mmput(mm);
> +}
> +
> +/*
> + * Instruction trace filtering: limiting the trace to certain
> + * instruction address ranges. Filters are ioctl()ed to us from
> + * userspace as ascii strings.
> + *
> + * Filter string format:
> + *
> + * ACTION SOURCE:RANGE_SPEC
> + * where ACTION is one of the
> + * * "filter": limit the trace to this region
> + * * "start": start tracing from this address
> + * * "stop": stop tracing at this address/region;
> + * SOURCE is either "file" or "kernel"
> + * RANGE_SPEC is
> + * * for "kernel": <start address>[/<size>]
> + * * for "file": <start address>[/<size>]@</path/to/object/file>
> + *
> + * if <size> is not specified, the range is treated as a single address.
> + */
> +enum {
> + IF_ACT_FILTER,
> + IF_ACT_START,
> + IF_ACT_STOP,
> + IF_SRC_FILE,
> + IF_SRC_KERNEL,
> + IF_SRC_FILEADDR,
> + IF_SRC_KERNELADDR,
> +};
> +
> +enum {
> + IF_STATE_ACTION = 0,
> + IF_STATE_SOURCE,
> + IF_STATE_END,
> +};
> +
> +static const match_table_t if_tokens = {
> + { IF_ACT_FILTER, "filter" },
> + { IF_ACT_START, "start" },
> + { IF_ACT_STOP, "stop" },
> + { IF_SRC_FILE, "file:%u/%u@%s" },
> + { IF_SRC_KERNEL, "kernel:%u/%u" },
> + { IF_SRC_FILEADDR, "file:%u@%s" },
> + { IF_SRC_KERNELADDR, "kernel:%u" },
> +};
> +
> +/*
> + * Itrace filter string parser
> + */
> +static int
> +perf_event_parse_itrace_filter(struct perf_event *event, char *fstr)
> +{
> + struct perf_itrace_filter filter;
> + char *start, *orig, *filename = NULL;
> + struct path path;
> + substring_t args[MAX_OPT_ARGS];
> + int state = IF_STATE_ACTION, token;
> + int ret = -EINVAL;
> +
> + orig = fstr = kstrdup(fstr, GFP_KERNEL);
> + if (!fstr)
> + return -ENOMEM;
> +
> + while ((start = strsep(&fstr, " ,\n")) != NULL) {
> + ret = -EINVAL;
> +
> + if (!*start)
> + continue;
> +
> + /* filter definition begins */
> + if (state == IF_STATE_ACTION)
> + memset(&filter, 0, sizeof(filter));
> +
> + token = match_token(start, if_tokens, args);
> + switch (token) {
> + case IF_ACT_FILTER:
> + case IF_ACT_START:
> + filter.filter = 1;
> +
> + case IF_ACT_STOP:
> + if (state != IF_STATE_ACTION)
> + goto fail;
> +
> + state = IF_STATE_SOURCE;
> + break;
> +
> + case IF_SRC_KERNELADDR:
> + case IF_SRC_KERNEL:
> + filter.kernel = 1;
> +
> + case IF_SRC_FILEADDR:
> + case IF_SRC_FILE:
> + if (state != IF_STATE_SOURCE)
> + goto fail;
> +
> + if (token == IF_SRC_FILE || token == IF_SRC_KERNEL)
> + filter.range = 1;
> +
> + *args[0].to = 0;
> + ret = kstrtoul(args[0].from, 0, &filter.offset);
> + if (ret)
> + goto fail;
> +
> + if (filter.range) {
> + *args[1].to = 0;
> + ret = kstrtoul(args[1].from, 0, &filter.size);
> + if (ret)
> + goto fail;
> + }
> +
> + if (token == IF_SRC_FILE) {
> + filename = match_strdup(&args[2]);
> + if (!filename) {
> + ret = -ENOMEM;
> + goto fail;
> + }
> + }
> +
> + state = IF_STATE_END;
> + break;
> +
> + default:
> + goto fail;
> + }
> +
> + /*
> + * Filter definition is fully parsed, validate and install it.
> + * Make sure that it doesn't contradict itself or the event's
> + * attribute.
> + */
> + if (state == IF_STATE_END) {
> + if (filter.kernel && event->attr.exclude_kernel)
> + goto fail;
> +
> + if (!filter.kernel) {
> + if (!filename)
> + goto fail;
> +
> + /* look up the path and grab its inode */
> + ret = kern_path(filename, LOOKUP_FOLLOW, &path);
> + if (ret)
> + goto fail_free_name;
> +
> + filter.inode = igrab(d_inode(path.dentry));
> + path_put(&path);
> + kfree(filename);
> + filename = NULL;
> + }
> +
> + ret = perf_itrace_filter_insert(event, &filter,
> + event->ctx->task);
> + if (ret)
> + goto fail;
> +
> + /* ready to consume more filters */
> + state = IF_STATE_ACTION;
> + }
> + }
> +
> + if (state != IF_STATE_ACTION)
> + goto fail;
> +
> + kfree(orig);
> +
> + return 0;
> +
> +fail_free_name:
> + kfree(filename);
> +fail:
> + perf_itrace_filters_clear(event);
> + kfree(orig);
> +
> + return ret;
> +}
> +
> +/*
> + * Filters are cloned in inherit_event() path to make sure child tracing is
> + * consistent with parent.
> + */
> +static int
> +perf_itrace_filters_clone(struct perf_event *to, struct perf_event *from,
> + struct task_struct *task)
> +{
> + struct perf_itrace_filter *filter;
> + int ret = -ENOMEM;
> +
> + mutex_lock(&from->itrace_filters_mutex);
> + list_for_each_entry_rcu(filter, &from->itrace_filters, entry) {
> + /* parent's filter must hold a reference to this inode */
> + if (WARN_ON_ONCE(!igrab(filter->inode)))
> + goto fail;
> +
> + ret = perf_itrace_filter_insert(to, filter, task);
> + if (ret) {
> + iput(filter->inode);
> + goto fail;
> + }
> + }
> +
> + ret = 0;
> +fail:
> + mutex_unlock(&from->itrace_filters_mutex);
> +
> + if (!ret)
> + ret = perf_event_itrace_filters_setup(to);
> + else
> + perf_itrace_filters_clear(to);
> +
> + return ret;
> +}
> +
> +static int
> +perf_event_set_itrace_filter(struct perf_event *event, char *filter_str)
> +{
> + int ret = 0;
> +
> + /*
> + * Since this is called in perf_ioctl() path, we're already holding
> + * ctx::mutex.
> + */
> + lockdep_assert_held(&event->ctx->mutex);
> +
> + /*
> + * For now, we only support filtering in per-task events; doing so
> + * for cpu-wide events requires additional context switching trickery,
> + * since same object code will be mapped at different virtual
> + * addresses in different processes.
> + */
> + if (!event->ctx->task)
> + return -EOPNOTSUPP;
> +
> + /* remove existing filters, if any */
> + perf_itrace_filters_clear(event);
> +
> + ret = perf_event_parse_itrace_filter(event, filter_str);
> + if (!ret) {
> + perf_itrace_filters_apply(event);
> +
> + ret = perf_event_itrace_filters_setup(event);
> + if (ret)
> + perf_itrace_filters_clear(event);
> + }
> +
> + return ret;
> +}
> +
> static int perf_event_set_filter(struct perf_event *event, void __user *arg)
> {
> char *filter_str;
> int ret = -EINVAL;
>
> - if (event->attr.type != PERF_TYPE_TRACEPOINT ||
> - !IS_ENABLED(CONFIG_EVENT_TRACING))
> + if ((event->attr.type != PERF_TYPE_TRACEPOINT ||
> + !IS_ENABLED(CONFIG_EVENT_TRACING)) &&
> + !has_itrace_filter(event))
> return -EINVAL;
>
> filter_str = strndup_user(arg, PAGE_SIZE);
> @@ -7180,6 +7735,8 @@ static int perf_event_set_filter(struct perf_event *event, void __user *arg)
> event->attr.type == PERF_TYPE_TRACEPOINT)
> ret = ftrace_profile_set_filter(event, event->attr.config,
> filter_str);
> + else if (has_itrace_filter(event))
> + ret = perf_event_set_itrace_filter(event, filter_str);
>
> kfree(filter_str);
> return ret;
> @@ -7921,13 +8478,14 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
> INIT_LIST_HEAD(&event->sibling_list);
> INIT_LIST_HEAD(&event->rb_entry);
> INIT_LIST_HEAD(&event->active_entry);
> + INIT_LIST_HEAD(&event->itrace_filters);
> INIT_HLIST_NODE(&event->hlist_entry);
>
> -
> init_waitqueue_head(&event->waitq);
> init_irq_work(&event->pending, perf_pending_event);
>
> mutex_init(&event->mmap_mutex);
> + mutex_init(&event->itrace_filters_mutex);
>
> atomic_long_set(&event->refcount, 1);
> event->cpu = cpu;
> @@ -9063,6 +9621,18 @@ inherit_event(struct perf_event *parent_event,
> get_ctx(child_ctx);
>
> /*
> + * Clone itrace filters from the parent, if any
> + */
> + if (has_itrace_filter(child_event)) {
> + if (perf_itrace_filters_clone(child_event, parent_event,
> + child)) {
> + put_ctx(child_ctx);
> + free_event(child_event);
> + return NULL;
> + }
> + }
> +
> + /*
> * Make the child state follow the state of the parent event,
> * not its attr.disabled bit. We hold the parent's mutex,
> * so we won't race with perf_event_{en, dis}able_family.
> --
> 2.6.2
>
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