The patch titled
signals: make task_struct->signal immutable/refcountable
has been added to the -mm tree. Its filename is
signals-make-task_struct-signal-immutable-refcountable.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: signals: make task_struct->signal immutable/refcountable
From: Oleg Nesterov <oleg@xxxxxxxxxx>
We have a lot of problems with accessing task_struct->signal, it can
"disappear" at any moment. Even current can't use its ->signal safely
after exit_notify(). ->siglock helps, but it is not convenient, not
always possible, and sometimes it makes sense to use task->signal even
after this task has already dead.
This patch adds the reference counter, sigcnt, into signal_struct. This
reference is owned by task_struct and it is dropped in
__put_task_struct(). Perhaps it makes sense to export
get/put_signal_struct() later, but currently I don't see the immediate
reason.
Rename __cleanup_signal() to free_signal_struct() and unexport it. With
the previous changes it does nothing except kmem_cache_free().
Change __exit_signal() to not clear/free ->signal, it will be freed when
the last reference to any thread in the thread group goes away.
Note:
- when the last thead exits signal->tty can point to nowhere, see
the next patch.
- with or without this patch signal_struct->count should go away,
or at least it should be "int nr_threads" for fs/proc. This will
be addressed later.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Alan Cox <alan@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 2 +-
kernel/exit.c | 3 ---
kernel/fork.c | 23 ++++++++++++++++-------
3 files changed, 17 insertions(+), 11 deletions(-)
diff -puN include/linux/sched.h~signals-make-task_struct-signal-immutable-refcountable include/linux/sched.h
--- a/include/linux/sched.h~signals-make-task_struct-signal-immutable-refcountable
+++ a/include/linux/sched.h
@@ -522,6 +522,7 @@ struct thread_group_cputimer {
* the locking of signal_struct.
*/
struct signal_struct {
+ atomic_t sigcnt;
atomic_t count;
atomic_t live;
@@ -2103,7 +2104,6 @@ extern void flush_thread(void);
extern void exit_thread(void);
extern void exit_files(struct task_struct *);
-extern void __cleanup_signal(struct signal_struct *);
extern void __cleanup_sighand(struct sighand_struct *);
extern void exit_itimers(struct signal_struct *);
diff -puN kernel/exit.c~signals-make-task_struct-signal-immutable-refcountable kernel/exit.c
--- a/kernel/exit.c~signals-make-task_struct-signal-immutable-refcountable
+++ a/kernel/exit.c
@@ -135,8 +135,6 @@ static void __exit_signal(struct task_st
* doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals.
*/
flush_sigqueue(&tsk->pending);
-
- tsk->signal = NULL;
tsk->sighand = NULL;
spin_unlock(&sighand->siglock);
@@ -151,7 +149,6 @@ static void __exit_signal(struct task_st
*/
task_rq_unlock_wait(tsk);
tty_kref_put(sig->tty);
- __cleanup_signal(sig);
}
}
diff -puN kernel/fork.c~signals-make-task_struct-signal-immutable-refcountable kernel/fork.c
--- a/kernel/fork.c~signals-make-task_struct-signal-immutable-refcountable
+++ a/kernel/fork.c
@@ -165,6 +165,18 @@ void free_task(struct task_struct *tsk)
}
EXPORT_SYMBOL(free_task);
+static inline void free_signal_struct(struct signal_struct *sig)
+{
+ thread_group_cputime_free(sig);
+ kmem_cache_free(signal_cachep, sig);
+}
+
+static inline void put_signal_struct(struct signal_struct *sig)
+{
+ if (atomic_dec_and_test(&sig->sigcnt))
+ free_signal_struct(sig);
+}
+
void __put_task_struct(struct task_struct *tsk)
{
WARN_ON(!tsk->exit_state);
@@ -173,6 +185,7 @@ void __put_task_struct(struct task_struc
exit_creds(tsk);
delayacct_tsk_free(tsk);
+ put_signal_struct(tsk->signal);
if (!profile_handoff_task(tsk))
free_task(tsk);
@@ -864,6 +877,7 @@ static int copy_signal(unsigned long clo
if (!sig)
return -ENOMEM;
+ atomic_set(&sig->sigcnt, 1);
atomic_set(&sig->count, 1);
atomic_set(&sig->live, 1);
init_waitqueue_head(&sig->wait_chldexit);
@@ -889,12 +903,6 @@ static int copy_signal(unsigned long clo
return 0;
}
-void __cleanup_signal(struct signal_struct *sig)
-{
- thread_group_cputime_free(sig);
- kmem_cache_free(signal_cachep, sig);
-}
-
static void copy_flags(unsigned long clone_flags, struct task_struct *p)
{
unsigned long new_flags = p->flags;
@@ -1245,6 +1253,7 @@ static struct task_struct *copy_process(
}
if (clone_flags & CLONE_THREAD) {
+ atomic_inc(¤t->signal->sigcnt);
atomic_inc(¤t->signal->count);
atomic_inc(¤t->signal->live);
p->group_leader = current->group_leader;
@@ -1291,7 +1300,7 @@ bad_fork_cleanup_mm:
mmput(p->mm);
bad_fork_cleanup_signal:
if (!(clone_flags & CLONE_THREAD))
- __cleanup_signal(p->signal);
+ free_signal_struct(p->signal);
bad_fork_cleanup_sighand:
__cleanup_sighand(p->sighand);
bad_fork_cleanup_fs:
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
origin.patch
linux-next.patch
posix-cpu-timers-reset-expire-cache-when-no-timer-is-running.patch
cpu-timers-simplify-rlimit_cpu-handling.patch
cpu-timers-cleanup-arm_timer.patch
cpu-timers-return-correct-previous-timer-reload-value.patch
cpu-timers-change-sigev_none-timer-implementation.patch
cpu-timers-assure-to-not-iterate-over-all-threads-in-fastpath_timer_check.patch
cpu-timers-optimize-run_posix_cpu_timers.patch
proc-cleanup-remove-unused-assignments.patch
kmod-add-init-function-to-usermodehelper.patch
exec-replace-call_usermodehelper_pipe-with-use-of-umh-init-function-and-resolve-limit.patch
umh-creds-convert-call_usermodehelper_keys-to-use-subprocess_info-init.patch
umh-creds-kill-subprocess_info-cred-logic.patch
call_usermodehelper-no-need-to-unblock-signals.patch
wait_for_helper-sigchld-from-user-space-can-lead-to-use-after-free.patch
call_usermodehelper-simplify-fix-umh_no_wait-case.patch
call_usermodehelper-umh_wait_exec-ignores-kernel_thread-failure.patch
coredump-factor-out-the-not-ispipe-file-checks.patch
coredump-cleanup-ispipe-code.patch
coredump-factor-out-put_cred-calls.patch
coredump-shift-down_writemmap_sem-into-coredump_wait.patch
exit-exit_notify-can-trust-signal-notify_count-0.patch
exit-change-zap_other_threads-to-count-sub-threads.patch
exit-avoid-sig-count-in-de_thread-__exit_signal-synchronization.patch
exit-avoid-sig-count-in-__exit_signal-to-detect-the-group-dead-case.patch
posix-cpu-timers-avoid-task-signal-=-null-checks.patch
ia64-ptrace_attach_sync_user_rbs-avoid-task-signal-=-null-checks.patch
fork-exit-move-tty_kref_put-outside-of-__cleanup_signal.patch
signals-make-task_struct-signal-immutable-refcountable.patch
signals-clear-signal-tty-when-the-last-thread-exits.patch
signals-kill-the-awful-task_rq_unlock_wait-hack.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
