From nobody Mon Dec 27 14:54:57 2021 X-Original-To: freebsd-hackers@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id C66711911D31 for ; Mon, 27 Dec 2021 14:55:06 +0000 (UTC) (envelope-from janm@transactionware.com) Received: from mail3.transactionware.com (mail.transactionware.com [203.14.245.7]) by mx1.freebsd.org (Postfix) with SMTP id 4JN1160vPxz4d0m for ; Mon, 27 Dec 2021 14:55:05 +0000 (UTC) (envelope-from janm@transactionware.com) Received: (qmail 38636 invoked by uid 907); 27 Dec 2021 14:55:03 -0000 Received: from i5E86400D.versanet.de (HELO smtpclient.apple) (94.134.64.13) (smtp-auth username janm, mechanism plain) by mail3.transactionware.com (qpsmtpd/0.84) with (ECDHE-RSA-AES256-GCM-SHA384 encrypted) ESMTPSA; Tue, 28 Dec 2021 01:55:03 +1100 Content-Type: text/plain; charset=utf-8 List-Id: Technical discussions relating to FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-hackers List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-hackers@freebsd.org Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.120.0.1.13\)) Subject: Re: closefrom blocking, wchan urdlck From: Jan Mikkelsen In-Reply-To: Date: Mon, 27 Dec 2021 15:54:57 +0100 Cc: freebsd-hackers@freebsd.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <2B3BA665-D42A-4B5F-AD2F-ED10E64A7276@transactionware.com> To: Konstantin Belousov X-Mailer: Apple Mail (2.3654.120.0.1.13) X-Rspamd-Queue-Id: 4JN1160vPxz4d0m X-Spamd-Bar: ---- Authentication-Results: mx1.freebsd.org; none X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[] X-ThisMailContainsUnwantedMimeParts: N > On 27 Dec 2021, at 14:52, Konstantin Belousov = wrote: >=20 > On Mon, Dec 27, 2021 at 01:39:11PM +0100, Jan Mikkelsen wrote: >> Hi, >>=20 >> (On 11.2) >>=20 >> I am occasionally seeing closefrom() block in a child process created = by a call to pdfork(). >>=20 >> When this does happen, it is very early after the process has = started, while other threads are being created elsewhere in the process. = I cannot reproduce it after the thread creation is complete. According = to the sigaction man page, this should be async signal safe. >>=20 >> Stack trace from the call to closefrom(): >>=20 >> * frame #0: 0x000000080090276c libthr.so.3`_umtx_op_err at = _umtx_op_err.S:37 >> frame #1: 0x00000008008f6121 = libthr.so.3`__thr_rwlock_rdlock(rwlock=3D, = flags=3D, tsp=3D) at thr_umtx.c:307:10 >> frame #2: 0x00000008008ff1ac libthr.so.3`_thr_rtld_rlock_acquire = [inlined] _thr_rwlock_rdlock(rwlock=3D0x0000000800911600, flags=3D0, = tsp=3D0x0000000000000000) at thr_umtx.h:232:10 >> frame #3: 0x00000008008ff19b = libthr.so.3`_thr_rtld_rlock_acquire(lock=3D0x0000000800911600) at = thr_rtld.c:125 >> frame #4: 0x000000080075332b = ld-elf.so.1`rlock_acquire(lock=3D0x0000000800765270, = lockstate=3D0x00007fffdfbfb8d0) at rtld_lock.c:208:2 >> frame #5: 0x000000080074ba20 = ld-elf.so.1`_rtld_bind(obj=3D0x0000000800769000, reloff=3D6072) at = rtld.c:861:5 >> frame #6: 0x0000000800747c7d ld-elf.so.1`_rtld_bind_start at = rtld_start.S:121 >> frame #7: 0x00000000006562d3 = prog`Twio::ProcHandle::spawn(this=3D, command=3D"/bin/echo", = args=3D0x0000000800d7e000, descriptor_mapping=3D, = descriptor_end=3D3) at prochandle_pdfork.cpp:308:2 > And where is the closefrom() call in the demonstrated trace? >=20 > What version of the system do you use? > You need at least cbdec8db18b533f6d7be (on HEAD) or a5659943e37a74c96e > (stable/13) for pdfork() to behave sanely. But you still not allowed = to > call non-async signal safe functions in the child before exec. This is 12.2-p11. I just noticed that I wrote 11.2 above, that is = incorrect. Frame 7 is a call to closefrom(). The child process calls dup2(), = closefrom(), signal() and then execv(). No other calls are made, and I = believe closefrom() is meant to be async signal safe. The commit you can apply cleanly to 12.2, I=E2=80=99m running a build = now. Are there other issues with pdfork in 12.2? Regards, Jan M.