Messages in this thread Patch in this message |  | | Date | Mon, 16 Jun 2008 18:20:18 +0400 | From | Oleg Nesterov <> | Subject | [PATCH 2/3] ptrace: never sleep in TASK_TRACED if SIGKILL'ed |
| |
Change ptrace_stop() to check if the task was killed unconditionally and simplify the "if (killed)" case - we can just return. Note that SIGKILL can be already dequeued if ptrace_stop() is called from do_exit(), that is why we use signal_group_exit().
The current behaviour is somewhat unpredictable. If we enter ptrace_stop() with the pending SIGKILL the result depends on arch_ptrace_stop_needed() and if it is true it also depends on was this signal private or group-wide if the caller is do_exit().
With this patch we never sleep in TASK_TRACED with the pending SIGKILL. This looks very logical, because only SIGKILL can wake up TASK_TRACED task, and the second SIGKILL (in general) has no effect.
Note: If the tracee was killed because another thread execs, we are not going to sleep anyway. If this is not desirable, we can check SIGNAL_GROUP_EXIT instead. But again, the current behaviour is not very predictable.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
--- 26-rc2/kernel/signal.c~2_PT_STOP_KILL 2008-06-08 16:15:25.000000000 +0400 +++ 26-rc2/kernel/signal.c 2008-06-10 20:06:24.000000000 +0400 @@ -1493,17 +1493,6 @@ static inline int may_ptrace_stop(void) } /* - * Return nonzero if there is a SIGKILL that should be waking us up. - * Called with the siglock held. - */ -static int sigkill_pending(struct task_struct *tsk) -{ - return ((sigismember(&tsk->pending.signal, SIGKILL) || - sigismember(&tsk->signal->shared_pending.signal, SIGKILL)) && - !unlikely(sigismember(&tsk->blocked, SIGKILL))); -} - -/* * This must be called with current->sighand->siglock held. * * This should be the path for all ptrace stops. @@ -1516,8 +1505,6 @@ static int sigkill_pending(struct task_s */ static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info) { - int killed = 0; - if (arch_ptrace_stop_needed(exit_code, info)) { /* * The arch code has something special to do before a @@ -1526,16 +1513,15 @@ static void ptrace_stop(int exit_code, i * calling arch_ptrace_stop, so we must release it now. * To preserve proper semantics, we must do this before * any signal bookkeeping like checking group_stop_count. - * Meanwhile, a SIGKILL could come in before we retake the - * siglock. That must prevent us from sleeping in TASK_TRACED. - * So after regaining the lock, we must check for SIGKILL. */ spin_unlock_irq(¤t->sighand->siglock); arch_ptrace_stop(exit_code, info); spin_lock_irq(¤t->sighand->siglock); - killed = sigkill_pending(current); } + if (unlikely(signal_group_exit(current->signal))) + return; + /* * If there is a group stop in progress, * we must participate in the bookkeeping. @@ -1550,7 +1536,7 @@ static void ptrace_stop(int exit_code, i __set_current_state(TASK_TRACED); spin_unlock_irq(¤t->sighand->siglock); read_lock(&tasklist_lock); - if (!unlikely(killed) && may_ptrace_stop()) { + if (may_ptrace_stop()) { do_notify_parent_cldstop(current, CLD_TRAPPED); read_unlock(&tasklist_lock); schedule();
|  |