Commit 4ada856f authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds

signals: clear signal->tty when the last thread exits

When the last thread exits signal->tty is freed, but the pointer is not
cleared and points to nowhere.

This is OK.  Nobody should use signal->tty lockless, and it is no longer
possible to take ->siglock.  However this looks wrong even if correct, and
the nice OOPS is better than subtle and hard to find bugs.

Change __exit_signal() to clear signal->tty under ->siglock.

Note: __exit_signal() needs more cleanups.  It should not check "sig !=
NULL" to detect the all-dead case and we have the same issues with
signal->stats.
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Acked-by: default avatarRoland McGrath <roland@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ea6d290c
...@@ -80,6 +80,7 @@ static void __exit_signal(struct task_struct *tsk) ...@@ -80,6 +80,7 @@ static void __exit_signal(struct task_struct *tsk)
{ {
struct signal_struct *sig = tsk->signal; struct signal_struct *sig = tsk->signal;
struct sighand_struct *sighand; struct sighand_struct *sighand;
struct tty_struct *uninitialized_var(tty);
BUG_ON(!sig); BUG_ON(!sig);
BUG_ON(!atomic_read(&sig->count)); BUG_ON(!atomic_read(&sig->count));
...@@ -93,6 +94,8 @@ static void __exit_signal(struct task_struct *tsk) ...@@ -93,6 +94,8 @@ static void __exit_signal(struct task_struct *tsk)
posix_cpu_timers_exit(tsk); posix_cpu_timers_exit(tsk);
if (thread_group_leader(tsk)) { if (thread_group_leader(tsk)) {
posix_cpu_timers_exit_group(tsk); posix_cpu_timers_exit_group(tsk);
tty = sig->tty;
sig->tty = NULL;
} else { } else {
/* /*
* If there is any task waiting for the group exit * If there is any task waiting for the group exit
...@@ -147,7 +150,7 @@ static void __exit_signal(struct task_struct *tsk) ...@@ -147,7 +150,7 @@ static void __exit_signal(struct task_struct *tsk)
* see account_group_exec_runtime(). * see account_group_exec_runtime().
*/ */
task_rq_unlock_wait(tsk); task_rq_unlock_wait(tsk);
tty_kref_put(sig->tty); tty_kref_put(tty);
} }
} }
......
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