The patch titled
Subject: kthread: introduce to_live_kthread()
has been added to the -mm tree. Its filename is
kthread-introduce-to_live_kthread.patch
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From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: kthread: introduce to_live_kthread()
"k->vfork_done != NULL" with a barrier() after to_kthread(k) in
task_get_live_kthread(k) looks unclear, and sub-optimal because we load
->vfork_done twice.
All we need is to ensure that we do not return to_kthread(NULL). Add a
new trivial helper which loads/checks ->vfork_done once, this also looks
more understandable.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/kthread.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)
diff -puN kernel/kthread.c~kthread-introduce-to_live_kthread kernel/kthread.c
--- a/kernel/kthread.c~kthread-introduce-to_live_kthread
+++ a/kernel/kthread.c
@@ -52,8 +52,21 @@ enum KTHREAD_BITS {
KTHREAD_IS_PARKED,
};
-#define to_kthread(tsk) \
- container_of((tsk)->vfork_done, struct kthread, exited)
+#define __to_kthread(vfork) \
+ container_of(vfork, struct kthread, exited)
+
+static inline struct kthread *to_kthread(struct task_struct *k)
+{
+ return __to_kthread(k->vfork_done);
+}
+
+static struct kthread *to_live_kthread(struct task_struct *k)
+{
+ struct completion *vfork = ACCESS_ONCE(k->vfork_done);
+ if (likely(vfork))
+ return __to_kthread(vfork);
+ return NULL;
+}
/**
* kthread_should_stop - should this kthread return now?
@@ -313,15 +326,8 @@ struct task_struct *kthread_create_on_cp
static struct kthread *task_get_live_kthread(struct task_struct *k)
{
- struct kthread *kthread;
-
get_task_struct(k);
- kthread = to_kthread(k);
- /* It might have exited */
- barrier();
- if (k->vfork_done != NULL)
- return kthread;
- return NULL;
+ return to_live_kthread(k);
}
/**
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
thinkpad-acpi-kill-hotkey_thread_mutex.patch
kthread-introduce-to_live_kthread.patch
kthread-kill-task_get_live_kthread.patch
lockdep-introduce-lock_acquire_exclusive-shared-helper-macros.patch
lglock-update-lockdep-annotations-to-report-recursive-local-locks.patch
ptrace-add-ability-to-retrieve-signals-without-removing-from-a-queue-v4.patch
selftest-add-a-test-case-for-ptrace_peeksiginfo.patch
signal-always-clear-sa_restorer-on-execve.patch
coredump-only-sigkill-should-interrupt-the-coredumping-task.patch
coredump-ensure-that-sigkill-always-kills-the-dumping-thread.patch
coredump-sanitize-the-setting-of-signal-group_exit_code.patch
coredump-introduce-dump_interrupted.patch
coredump-factor-out-the-setting-of-pf_dumpcore.patch
coredump-change-wait_for_dump_helpers-to-use-wait_event_interruptible.patch
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