From owner-freebsd-hackers@freebsd.org Mon Nov 30 09:44:27 2020 Return-Path: Delivered-To: freebsd-hackers@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 939754751D6 for ; Mon, 30 Nov 2020 09:44:27 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4Cl0gZ4wlnz4qTj; Mon, 30 Nov 2020 09:44:26 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.16.1/8.16.1) with ESMTPS id 0AU9iHvj098483 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Mon, 30 Nov 2020 11:44:20 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua 0AU9iHvj098483 Received: (from kostik@localhost) by tom.home (8.16.1/8.16.1/Submit) id 0AU9iHWo098482; Mon, 30 Nov 2020 11:44:17 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Mon, 30 Nov 2020 11:44:17 +0200 From: Konstantin Belousov To: Alan Somers Cc: FreeBSD Hackers Subject: Re: Why don't lio_listio's signals get delivered? Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on tom.home X-Rspamd-Queue-Id: 4Cl0gZ4wlnz4qTj X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=gmail.com (policy=none); spf=softfail (mx1.freebsd.org: 2001:470:d5e7:1::1 is neither permitted nor denied by domain of kostikbel@gmail.com) smtp.mailfrom=kostikbel@gmail.com X-Spamd-Result: default: False [-2.00 / 15.00]; ARC_NA(0.00)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; DMARC_POLICY_SOFTFAIL(0.10)[gmail.com : No valid SPF, No valid DKIM,none]; RCVD_TLS_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; RBL_DBL_DONT_QUERY_IPS(0.00)[2001:470:d5e7:1::1:from]; FREEMAIL_FROM(0.00)[gmail.com]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; HAS_XAW(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_SPF_SOFTFAIL(0.00)[~all:c]; SPAMHAUS_ZRD(0.00)[2001:470:d5e7:1::1:from:127.0.2.255]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; TO_DN_ALL(0.00)[]; NEURAL_HAM_SHORT(-1.00)[-1.000]; RCPT_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:6939, ipnet:2001:470::/32, country:US]; SUBJECT_ENDS_QUESTION(1.00)[]; MAILMAN_DEST(0.00)[freebsd-hackers]; RCVD_COUNT_TWO(0.00)[2] X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 30 Nov 2020 09:44:27 -0000 On Sun, Nov 29, 2020 at 05:54:32PM -0700, Alan Somers wrote: > I'm investigating https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=220398 > . What happens is that lio_listio sends a signal to the current process > (synchronously, from within the lio_listio syscall itself, not after some > I/O completes). With dtrace, I've verified that the signal isn't masked, > that it is caught, and that signotify and tdsigwakeup do get called. But > after lio_listio returns, the process never receives the signal. If it > registers a handler, the handler never gets called. If I set the signal to > SIGTERM, the process doesn't get terminated. It's as if the signal is > ignored. Asynchronously generated signals still work, however. > > What's going on? My knowledge of signal-delivery internals is running out, > and I would appreciate some help. > > Steps to reproduce: > $ cd /usr/tests/sys/aio > $ kyua debug lio_test:lio_listio_empty_nowait_signal > > Stack trace at the time the signal looks like it's being delivered: > kernel`tdsendsignal+0x4e1 > kernel`kern_lio_listio+0x493 > kernel`sys_lio_listio+0xc2 > kernel`amd64_syscall+0x12e > kernel`0xffffffff81007e1e > > lio_listio is attempting to send this signal via aio_sendsig, 24 lines from > the bottom of kern_lio_listio. Yes, the signal is queued to the current process, but then, several lines below it, it is dequeued. Look at the block with if (lj->lioj_count == 0) right above the finalization of error code. Problem is that ksi is embedded into aioliojob, and the later needs to be freed there when nitems == 0, because there is no callback. Perhaps, if you need signal to be delivered, we need to allocate ksi just in this case. BTW, I think there is a similar problem with knote, it is not delivered to userspace because knote is signalled but then deleted from kq before syscall returns.