From: Christian Brauner <christian.brauner@ubuntu.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: libc-alpha <libc-alpha@sourceware.org>,
Joseph Myers <joseph@codesourcery.com>
Subject: Re: [RFC PATCH glibc 3/8] nptl: Start new threads with all signals blocked [BZ #25098]
Date: Mon, 23 Mar 2020 18:05:03 +0100 [thread overview]
Message-ID: <20200323170503.dkaad3zmwe5owc4p@wittgenstein> (raw)
In-Reply-To: <1742466479.7642.1584982932053.JavaMail.zimbra@efficios.com>
On Mon, Mar 23, 2020 at 01:02:12PM -0400, Mathieu Desnoyers via Libc-alpha wrote:
> ----- On Mar 23, 2020, at 11:31 AM, Christian Brauner christian.brauner@ubuntu.com wrote:
>
> > On Mon, Mar 23, 2020 at 09:16:02AM -0400, Mathieu Desnoyers via Libc-alpha
> > wrote:
> >> From: Florian Weimer <fweimer@redhat.com>
> >>
> >> 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
> >
> > This could be a new clone3() flag. If someone wants to send a patch I'd
> > take it.
>
> I agree that it would be a nice improvement to alleviate the overhead of
> tweaking the signal masks on thread creation. I suspect the code proposed in
> this patch is still needed, because glibc would have to support the currently
> existing kernels. The improvement you envision involves adding this new flag
> into the Linux kernel clone3 system call and then wiring up glibc support.
>
> I don't expect this should delay rseq integration into glibc ?
Oh no, I wasn't trying to say that rseq() in glibc should be blocked on
this, not at all. I was just saying we should probably do this since
it's a valuable improvement.
Christian
next prev parent reply other threads:[~2020-03-23 17:05 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-23 13:15 [RFC PATCH glibc 0/8] Restartable Sequences enablement Mathieu Desnoyers via Libc-alpha
2020-03-23 13:16 ` [RFC PATCH glibc 1/8] Introduce <elf_machine_sym_no_match.h> Mathieu Desnoyers via Libc-alpha
2020-03-23 14:51 ` H.J. Lu via Libc-alpha
2020-03-23 17:04 ` Mathieu Desnoyers via Libc-alpha
2020-03-23 13:16 ` [RFC PATCH glibc 2/8] Implement __libc_early_init Mathieu Desnoyers via Libc-alpha
2020-03-23 13:16 ` [RFC PATCH glibc 3/8] nptl: Start new threads with all signals blocked [BZ #25098] Mathieu Desnoyers via Libc-alpha
2020-03-23 15:31 ` Christian Brauner
2020-03-23 17:02 ` Mathieu Desnoyers via Libc-alpha
2020-03-23 17:05 ` Christian Brauner [this message]
2020-04-22 16:38 ` Carlos O'Donell via Libc-alpha
2020-03-23 13:16 ` [RFC PATCH glibc 4/8] glibc: Perform rseq(2) registration at C startup and thread creation (v16) Mathieu Desnoyers via Libc-alpha
2020-03-23 22:01 ` Joseph Myers
2020-03-24 13:08 ` Mathieu Desnoyers via Libc-alpha
2020-03-24 18:58 ` Joseph Myers
2020-03-24 19:44 ` Mathieu Desnoyers via Libc-alpha
2020-03-23 13:16 ` [RFC PATCH glibc 5/8] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux (v7) Mathieu Desnoyers via Libc-alpha
2020-03-23 13:16 ` [RFC PATCH glibc 6/8] support record failure: allow use from constructor Mathieu Desnoyers via Libc-alpha
2020-03-23 13:16 ` [RFC PATCH glibc 7/8] support: implement xpthread key create/delete (v4) Mathieu Desnoyers via Libc-alpha
2020-03-23 13:16 ` [RFC PATCH glibc 8/8] rseq registration tests (v9) Mathieu Desnoyers via Libc-alpha
-- strict thread matches above, loose matches on Subject: below --
2020-03-19 14:41 [RFC PATCH glibc 0/8] Restartable Sequences enablement Mathieu Desnoyers via Libc-alpha
2020-03-19 14:41 ` [RFC PATCH glibc 3/8] nptl: Start new threads with all signals blocked [BZ #25098] Mathieu Desnoyers via Libc-alpha
2020-01-08 14:58 [RFC PATCH glibc 0/8] Restartable Sequences enablement Mathieu Desnoyers
2020-01-08 14:58 ` [RFC PATCH glibc 3/8] nptl: Start new threads with all signals blocked [BZ #25098] Mathieu Desnoyers
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