[PATCH] copy_process: cleanup bad_fork_cleanup_signal

__exit_signal() does important cleanups atomically under ->siglock.  It is
also called from copy_process's error path.  This is not good, for example we
can't move __unhash_process() under ->siglock for that reason.

We should not mix these 2 paths, just look at ugly 'if (p->sighand)' under
'bad_fork_cleanup_sighand:' label.  For copy_process() case it is sufficient
to just backout copy_signal(), nothing more.

Again, nobody can see this task yet.  For CLONE_THREAD case we just decrement
signal->count, otherwise nobody can see this ->signal and we can free it
lockless.

This patch assumes it is safe to do exit_thread_group_keys() without
tasklist_lock.

Signed-off-by: Oleg Nesterov <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Acked-by: David Howells <[email protected]>
Signed-off-by: Adrian Bunk <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 69c2a1e1529e9dfdb95394bc105ec1f8d400da2d..7dd430b697aa179db7bfc32e2fd4106b231563cb 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1149,7 +1149,7 @@ extern void flush_thread(void);
 extern void exit_thread(void);
 
 extern void exit_files(struct task_struct *);
-extern void exit_signal(struct task_struct *);
+extern void __cleanup_signal(struct signal_struct *);
 extern void __exit_signal(struct task_struct *);
 extern void __exit_sighand(struct task_struct *);
 extern void exit_itimers(struct signal_struct *);

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 15e1d9736b1bb9fc130b27a81fdb8109b7fe02b5..3af03b19c9830275c77ef99f98c6a22e76a79a7f 100644 (file)
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -210,7 +210,6 @@ extern kmem_cache_t *names_cachep;
 extern kmem_cache_t    *files_cachep;
 extern kmem_cache_t    *filp_cachep;
 extern kmem_cache_t    *fs_cachep;
-extern kmem_cache_t    *signal_cachep;
 extern kmem_cache_t    *sighand_cachep;
 extern kmem_cache_t    *bio_cachep;
 

diff --git a/kernel/fork.c b/kernel/fork.c
index 8a46ad52be8f3dabd44f6ccf3a2ccf4a37f58794..0aff28cdbadd0c7d45332ba4e8db1995b61371b3 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -84,7 +84,7 @@ static kmem_cache_t *task_struct_cachep;
 #endif
 
 /* SLAB cache for signal_struct structures (tsk->signal) */
-kmem_cache_t *signal_cachep;
+static kmem_cache_t *signal_cachep;
 
 /* SLAB cache for sighand_struct structures (tsk->sighand) */
 kmem_cache_t *sighand_cachep;
@@ -872,6 +872,22 @@ static inline int copy_signal(unsigned long clone_flags, struct task_struct * ts
        return 0;
 }
 
+void __cleanup_signal(struct signal_struct *sig)
+{
+       exit_thread_group_keys(sig);
+       kmem_cache_free(signal_cachep, sig);
+}
+
+static inline void cleanup_signal(struct task_struct *tsk)
+{
+       struct signal_struct *sig = tsk->signal;
+
+       atomic_dec(&sig->live);
+
+       if (atomic_dec_and_test(&sig->count))
+               __cleanup_signal(sig);
+}
+
 static inline void copy_flags(unsigned long clone_flags, struct task_struct *p)
 {
        unsigned long new_flags = p->flags;
@@ -1206,10 +1222,9 @@ bad_fork_cleanup_mm:
        if (p->mm)
                mmput(p->mm);
 bad_fork_cleanup_signal:
-       exit_signal(p);
+       cleanup_signal(p);
 bad_fork_cleanup_sighand:
-       if (p->sighand)
-               __exit_sighand(p);
+       __exit_sighand(p);
 bad_fork_cleanup_fs:
        exit_fs(p); /* blocking */
 bad_fork_cleanup_files:

diff --git a/kernel/signal.c b/kernel/signal.c
index 1d7f4463c32d15c14a2b1f9e366da57a35ab20ac..54e9ef673e68623079658cd38c5837c4f7a619db 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -395,23 +395,10 @@ void __exit_signal(struct task_struct *tsk)
        clear_tsk_thread_flag(tsk,TIF_SIGPENDING);
        flush_sigqueue(&tsk->pending);
        if (sig) {
-               /*
-                * We are cleaning up the signal_struct here.
-                */
-               exit_thread_group_keys(sig);
-               kmem_cache_free(signal_cachep, sig);
+               __cleanup_signal(sig);
        }
 }
 
-void exit_signal(struct task_struct *tsk)
-{
-       atomic_dec(&tsk->signal->live);
-
-       write_lock_irq(&tasklist_lock);
-       __exit_signal(tsk);
-       write_unlock_irq(&tasklist_lock);
-}
-
 /*
  * Flush all handlers for a task.
  */