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authorOleg Nesterov <oleg@redhat.com>2012-05-11 10:59:07 +1000
committerAl Viro <viro@zeniv.linux.org.uk>2012-05-23 22:09:21 -0400
commite73f8959af0439d114847eab5a8a5ce48f1217c4 (patch)
tree47f056093590a5e5552e3a75f163e1f798063bda /kernel/task_work.c
parent62366c88b29c5a32e1531142092f98eaf49b1103 (diff)
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task_work_add: generic process-context callbacks
Provide a simple mechanism that allows running code in the (nonatomic) context of the arbitrary task. The caller does task_work_add(task, task_work) and this task executes task_work->func() either from do_notify_resume() or from do_exit(). The callback can rely on PF_EXITING to detect the latter case. "struct task_work" can be embedded in another struct, still it has "void *data" to handle the most common/simple case. This allows us to kill the ->replacement_session_keyring hack, and potentially this can have more users. Performance-wise, this adds 2 "unlikely(!hlist_empty())" checks into tracehook_notify_resume() and do_exit(). But at the same time we can remove the "replacement_session_keyring != NULL" checks from arch/*/signal.c and exit_creds(). Note: task_work_add/task_work_run abuses ->pi_lock. This is only because this lock is already used by lookup_pi_state() to synchronize with do_exit() setting PF_EXITING. Fortunately the scope of this lock in task_work.c is really tiny, and the code is unlikely anyway. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: David Howells <dhowells@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Richard Kuo <rkuo@codeaurora.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Alexander Gordeev <agordeev@redhat.com> Cc: Chris Zankel <chris@zankel.net> Cc: David Smith <dsmith@redhat.com> Cc: "Frank Ch. Eigler" <fche@redhat.com> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Larry Woodman <lwoodman@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Tejun Heo <tj@kernel.org> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'kernel/task_work.c')
-rw-r--r--kernel/task_work.c84
1 files changed, 84 insertions, 0 deletions
diff --git a/kernel/task_work.c b/kernel/task_work.c
new file mode 100644
index 000000000000..82d1c794066d
--- /dev/null
+++ b/kernel/task_work.c
@@ -0,0 +1,84 @@
+#include <linux/spinlock.h>
+#include <linux/task_work.h>
+#include <linux/tracehook.h>
+
+int
+task_work_add(struct task_struct *task, struct task_work *twork, bool notify)
+{
+ unsigned long flags;
+ int err = -ESRCH;
+
+#ifndef TIF_NOTIFY_RESUME
+ if (notify)
+ return -ENOTSUPP;
+#endif
+ /*
+ * We must not insert the new work if the task has already passed
+ * exit_task_work(). We rely on do_exit()->raw_spin_unlock_wait()
+ * and check PF_EXITING under pi_lock.
+ */
+ raw_spin_lock_irqsave(&task->pi_lock, flags);
+ if (likely(!(task->flags & PF_EXITING))) {
+ hlist_add_head(&twork->hlist, &task->task_works);
+ err = 0;
+ }
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+
+ /* test_and_set_bit() implies mb(), see tracehook_notify_resume(). */
+ if (likely(!err) && notify)
+ set_notify_resume(task);
+ return err;
+}
+
+struct task_work *
+task_work_cancel(struct task_struct *task, task_work_func_t func)
+{
+ unsigned long flags;
+ struct task_work *twork;
+ struct hlist_node *pos;
+
+ raw_spin_lock_irqsave(&task->pi_lock, flags);
+ hlist_for_each_entry(twork, pos, &task->task_works, hlist) {
+ if (twork->func == func) {
+ hlist_del(&twork->hlist);
+ goto found;
+ }
+ }
+ twork = NULL;
+ found:
+ raw_spin_unlock_irqrestore(&task->pi_lock, flags);
+
+ return twork;
+}
+
+void task_work_run(void)
+{
+ struct task_struct *task = current;
+ struct hlist_head task_works;
+ struct hlist_node *pos;
+
+ raw_spin_lock_irq(&task->pi_lock);
+ hlist_move_list(&task->task_works, &task_works);
+ raw_spin_unlock_irq(&task->pi_lock);
+
+ if (unlikely(hlist_empty(&task_works)))
+ return;
+ /*
+ * We use hlist to save the space in task_struct, but we want fifo.
+ * Find the last entry, the list should be short, then process them
+ * in reverse order.
+ */
+ for (pos = task_works.first; pos->next; pos = pos->next)
+ ;
+
+ for (;;) {
+ struct hlist_node **pprev = pos->pprev;
+ struct task_work *twork = container_of(pos, struct task_work,
+ hlist);
+ twork->func(twork);
+
+ if (pprev == &task_works.first)
+ break;
+ pos = container_of(pprev, struct hlist_node, next);
+ }
+}