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authorOleg Nesterov <oleg@redhat.com>2010-05-26 14:43:16 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-05-27 09:12:46 -0700
commitea6d290ca34c4fd91b7348338c0cc7bdeff94a35 (patch)
tree6e9bd367650d9233c5b6cf1059845f17cb1bc460
parent4dec2a91fd7e8815d730afbfdcf085cbf53433ac (diff)
downloadop-kernel-dev-ea6d290ca34c4fd91b7348338c0cc7bdeff94a35.zip
op-kernel-dev-ea6d290ca34c4fd91b7348338c0cc7bdeff94a35.tar.gz
signals: make task_struct->signal immutable/refcountable
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@redhat.com> Cc: Alan Cox <alan@linux.intel.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <peterz@infradead.org> Acked-by: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/sched.h2
-rw-r--r--kernel/exit.c3
-rw-r--r--kernel/fork.c23
3 files changed, 17 insertions, 11 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a95a245..32e309d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -527,6 +527,7 @@ struct thread_group_cputimer {
* the locking of signal_struct.
*/
struct signal_struct {
+ atomic_t sigcnt;
atomic_t count;
atomic_t live;
@@ -2101,7 +2102,6 @@ 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 --git a/kernel/exit.c b/kernel/exit.c
index 4a72f17..92af5cd 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -134,8 +134,6 @@ static void __exit_signal(struct task_struct *tsk)
* doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals.
*/
flush_sigqueue(&tsk->pending);
-
- tsk->signal = NULL;
tsk->sighand = NULL;
spin_unlock(&sighand->siglock);
@@ -150,7 +148,6 @@ static void __exit_signal(struct task_struct *tsk)
*/
task_rq_unlock_wait(tsk);
tty_kref_put(sig->tty);
- __cleanup_signal(sig);
}
}
diff --git a/kernel/fork.c b/kernel/fork.c
index b7879ef..e08e301 100644
--- a/kernel/fork.c
+++ b/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_struct *tsk)
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 clone_flags, struct task_struct *tsk)
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 clone_flags, struct task_struct *tsk)
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;
@@ -1248,6 +1256,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
}
if (clone_flags & CLONE_THREAD) {
+ atomic_inc(&current->signal->sigcnt);
atomic_inc(&current->signal->count);
atomic_inc(&current->signal->live);
p->group_leader = current->group_leader;
@@ -1294,7 +1303,7 @@ 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:
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