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Sat, 13 May 2023 05:47:03 -0400 Received: from debbugs.gnu.org ([209.51.188.43]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1pxlqA-0008Jo-GI for bug-guix@gnu.org; Sat, 13 May 2023 05:47:03 -0400 Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1pxlqA-0000mK-Bc for bug-guix@gnu.org; Sat, 13 May 2023 05:47:02 -0400 X-Loop: help-debbugs@gnu.org Subject: bug#63190: [Shepherd] Nested calls lead to a hang Resent-From: Ludovic =?UTF-8?Q?Court=C3=A8s?= Original-Sender: "Debbugs-submit" Resent-CC: bug-guix@gnu.org Resent-Date: Sat, 13 May 2023 09:47:02 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 63190 X-GNU-PR-Package: guix X-GNU-PR-Keywords: To: Brian Cully Cc: 63190@debbugs.gnu.org, Bruno Victal Received: via spool by 63190-submit@debbugs.gnu.org id=B63190.16839711642911 (code B ref 63190); Sat, 13 May 2023 09:47:02 +0000 Received: (at 63190) by debbugs.gnu.org; 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Received: from 91-160-117-201.subs.proxad.net ([91.160.117.201] helo=ribbon) by fencepost.gnu.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pxlp5-0004ej-1f; Sat, 13 May 2023 05:45:55 -0400 From: Ludovic =?UTF-8?Q?Court=C3=A8s?= References: <87wn1lid69.fsf@gnu.org> <87h6shduaw.fsf@psyduck.jhoto.kublai.com> Date: Sat, 13 May 2023 11:45:51 +0200 In-Reply-To: <87h6shduaw.fsf@psyduck.jhoto.kublai.com> (Brian Cully's message of "Fri, 12 May 2023 19:01:08 -0400") Message-ID: <87h6sg1s4w.fsf@gnu.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-BeenThere: bug-guix@gnu.org List-Id: Bug reports for GNU Guix List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-guix-bounces+larch=yhetil.org@gnu.org Sender: bug-guix-bounces+larch=yhetil.org@gnu.org X-Migadu-Flow: FLOW_IN X-Migadu-Country: US ARC-Seal: i=1; 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bh=khl/Tfc7wTmjVIrqDgyl4B111sJXbNDww8Rd51v3r4s=; b=YvRRoQBNlPWGWlFJo6qYsVxC6PLr/fQuxCo9xX0kM3UTz2wIJ0C72/sPEb1cScmMvRFtRz cwjYuWzbuj84K1pE6FGCrPH3xsioT4GsULPRduq6LY2pTMSG5hHB3GnkN1P/d76+h3MZdF ZZgz3nOIXJXU+CKIoPi+jqIexb073v5yfqf0PRPi+bGf/Jc3zYS+5X9gMFx/VEA/2fNEM6 s4wvDD3iyq84MuabwCRK5/5BiF+8WI9/Iy/mEwjBxkxr+E+fvG9eLJ3sFZkFwlR7XI7/Ph +t2Oic7nEYFsPaKrkV2jUSDg1tXaH+URLguLEo0b/boPEsY8Z7a4WA09R/1SFQ== X-Migadu-Scanner: scn1.migadu.com Authentication-Results: aspmx1.migadu.com; dkim=fail ("headers rsa verify failed") header.d=gnu.org header.s=fencepost-gnu-org header.b=cxB7Lrh6; dmarc=pass (policy=none) header.from=gnu.org; spf=pass (aspmx1.migadu.com: domain of "bug-guix-bounces+larch=yhetil.org@gnu.org" designates 209.51.188.17 as permitted sender) smtp.mailfrom="bug-guix-bounces+larch=yhetil.org@gnu.org" X-Migadu-Spam-Score: -4.08 X-Spam-Score: -4.08 X-Migadu-Queue-Id: 503DBC893 X-TUID: kLkNyye0Q0f7 Brian Cully skribis: > Ludovic Court=C3=A8s writes: > >> (Whether that leads to a deadlock depends; at first sight, I=E2=80=99d s= ay >> there=E2=80=99s no reason for this to deadlock in general, but you can of >> course >> end up with a logic bug like A starts B, which spawns a client to >> start >> A, which doesn=E2=80=99t start because it=E2=80=99s waiting for B.) > > It's been a while since I looked at this, but my rough recollection is > the deadlock occurs because shepherd can only process one request over > its socket at a time. That=E2=80=99s not the case in 0.9: it can process several requests concurrently. However, as I wrote in a followup message, the client socket created by (gnu services herd) lacks SOCK_NONBLOCK, which can thus block the process on reads and writes. Ludo=E2=80=99.