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ptrace: ptrace_detach() can no longer race with SIGKILL

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ptrace_detach() re-checks ->ptrace under tasklist lock and calls
release_task() if __ptrace_detach() returns true.  This was needed because
the __TASK_TRACED tracee could be killed/untraced, and it could even pass
exit_notify() before we take tasklist_lock.

But this is no longer possible after 9899d11f65 "ptrace: ensure
arch_ptrace/ptrace_request can never race with SIGKILL".  We can turn
these checks into WARN_ON() and remove release_task().

While at it, document the setting of child->exit_code.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Pavel Labath <labath@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2015-04-16 12:47:32 -07:00 committed by Linus Torvalds
parent b72c186999
commit 64a4096c5c
1 changed files with 9 additions and 10 deletions
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19
kernel/ptrace.c
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@ -456,8 +456,6 @@ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
static int ptrace_detach(struct task_struct *child, unsigned int data)
{
bool dead = false;
if (!valid_signal(data))
return -EIO;
@ -467,18 +465,19 @@ static int ptrace_detach(struct task_struct *child, unsigned int data)
write_lock_irq(&tasklist_lock);
/*
* This child can be already killed. Make sure de_thread() or
* our sub-thread doing do_wait() didn't do release_task() yet.
* We rely on ptrace_freeze_traced(). It can't be killed and
* untraced by another thread, it can't be a zombie.
*/
if (child->ptrace) {
child->exit_code = data;
dead = __ptrace_detach(current, child);
}
WARN_ON(!child->ptrace || child->exit_state);
/*
* tasklist_lock avoids the race with wait_task_stopped(), see
* the comment in ptrace_resume().
*/
child->exit_code = data;
__ptrace_detach(current, child);
write_unlock_irq(&tasklist_lock);
proc_ptrace_connector(child, PTRACE_DETACH);
if (unlikely(dead))
release_task(child);
return 0;
}