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>
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index b9ca903..b2dd091 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -49,6 +49,7 @@
#include <linux/sched.h>
#include <linux/ptrace.h>
#include <linux/security.h>
+#include <linux/task_work.h>
struct linux_binprm;
/*
@@ -164,8 +165,10 @@
*/
static inline void set_notify_resume(struct task_struct *task)
{
+#ifdef TIF_NOTIFY_RESUME
if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
kick_process(task);
+#endif
}
/**
@@ -185,6 +188,14 @@
{
if (current->replacement_session_keyring)
key_replace_session_keyring();
+ /*
+ * The caller just cleared TIF_NOTIFY_RESUME. This barrier
+ * pairs with task_work_add()->set_notify_resume() after
+ * hlist_add_head(task->task_works);
+ */
+ smp_mb__after_clear_bit();
+ if (unlikely(!hlist_empty(¤t->task_works)))
+ task_work_run();
}
#endif /* <linux/tracehook.h> */