Re: [PATCH] nptl: Start new threads with all signals blocked [BZ #25098]

[Florian Weimer <fweimer@redhat.com>]

* Christian Brauner:

> On Mon, Oct 14, 2019 at 02:33:43PM +0200, Florian Weimer wrote:
>> New threads inherit the signal mask from the current thread.  This
>> means that signal handlers can run on the newly created thread
>> immediately after the kernel has created the userspace thread, even
>> before glibc has initialized the TCB.  Consequently, new threads can
>> observe uninitialized ctype data, among other things.
>> 
>> To address this, block all signals before starting the thread, and
>> pass the original signal mask to the start routine wrapper.  On the
>> new thread, first perform all thread initialization, and then unblock
>> signals.
>> 
>> The cost of doing this is two rt_sigprocmask system calls on the old
>> thread, and one rt_sigprocmask system call on the new thread.  (If
>> there was a way to clone a new thread with a signals disabled, this
>
> He, do I see a growing wishlist? :)

Maybe.  I think the handler reset is more important because as
Adhemerval explained, it saves many more system calls.

Thanks,
Florian