perf events: Clean up pid passing

The kernel perf event creation path shouldn't use find_task_by_vpid()
because a vpid exists in a specific namespace. find_task_by_vpid() uses
current's pid namespace which isn't always the correct namespace to use
for the vpid in all the places perf_event_create_kernel_counter() (and
thus find_get_context()) is called.

The goal is to clean up pid namespace handling and prevent bugs like:

	https://bugzilla.kernel.org/show_bug.cgi?id=17281

Instead of using pids switch find_get_context() to use task struct
pointers directly. The syscall is responsible for resolving the pid to
a task struct. This moves the pid namespace resolution into the syscall
much like every other syscall that takes pid parameters.

Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Robin Green <greenrd@greenrd.org>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
LKML-Reference: <a134e5e392ab0204961fd1a62c84a222bf5874a9.1284407763.git.matthltc@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 10 insertions, 11 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 3f5309db72f1..86f394e15d53 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2053,15 +2053,14 @@ errout:
 }
 
 static struct perf_event_context *
-find_get_context(struct pmu *pmu, pid_t pid, int cpu)
+find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
 {
         struct perf_event_context *ctx;
         struct perf_cpu_context *cpuctx;
-        struct task_struct *task;
         unsigned long flags;
         int ctxn, err;
 
-        if (pid == -1 && cpu != -1) {
+        if (!task && cpu != -1) {
                 /* Must be root to operate on a CPU event: */
                 if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
                         return ERR_PTR(-EACCES);
@@ -2084,10 +2083,6 @@ find_get_context(struct pmu *pmu, pid_t pid, int cpu)
                 return ctx;
         }
 
-        task = find_lively_task_by_vpid(pid);
-        if (IS_ERR(task))
-                return (void*)task;
-
         err = -EINVAL;
         ctxn = pmu->task_ctx_nr;
         if (ctxn < 0)
@@ -5527,6 +5522,7 @@ SYSCALL_DEFINE5(perf_event_open,
         struct perf_event_context *ctx;
         struct file *event_file = NULL;
         struct file *group_file = NULL;
+        struct task_struct *task = NULL;
         struct pmu *pmu;
         int event_fd;
         int fput_needed = 0;
@@ -5581,10 +5577,13 @@ SYSCALL_DEFINE5(perf_event_open,
         if ((pmu->task_ctx_nr == perf_sw_context) && group_leader)
                 pmu = group_leader->pmu;
 
+        if (pid != -1)
+                task = find_lively_task_by_vpid(pid);
+
         /*
          * Get the target context (task or percpu):
          */
-        ctx = find_get_context(pmu, pid, cpu);
+        ctx = find_get_context(pmu, task, cpu);
         if (IS_ERR(ctx)) {
                 err = PTR_ERR(ctx);
                 goto err_group_fd;
@@ -5666,11 +5665,11 @@ err_fd:
  *
  * @attr: attributes of the counter to create
  * @cpu: cpu in which the counter is bound
- * @pid: task to profile
+ * @task: task to profile (NULL for percpu)
  */
 struct perf_event *
 perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
-                                 pid_t pid,
+                                 struct task_struct *task,
                                  perf_overflow_handler_t overflow_handler)
 {
         struct perf_event_context *ctx;
@@ -5687,7 +5686,7 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
                 goto err;
         }
 
-        ctx = find_get_context(event->pmu, pid, cpu);
+        ctx = find_get_context(event->pmu, task, cpu);
         if (IS_ERR(ctx)) {
                 err = PTR_ERR(ctx);
                 goto err_free;