From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.4 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 3755420960 for ; Mon, 10 Apr 2017 23:49:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753302AbdDJXtg (ORCPT ); Mon, 10 Apr 2017 19:49:36 -0400 Received: from mail-pf0-f180.google.com ([209.85.192.180]:34943 "EHLO mail-pf0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752497AbdDJXte (ORCPT ); Mon, 10 Apr 2017 19:49:34 -0400 Received: by mail-pf0-f180.google.com with SMTP id i5so40206864pfc.2 for ; Mon, 10 Apr 2017 16:49:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=/HZISRTpvYHYIp98Z09QG9oWLbCtF0AHFib4N/wAOUY=; b=g79QojF1MxFZPd4sqDvVzfiK057AwBKPPwouIMC6YkjY8/uAahudPYAlcxv5zyx0gs 3uAS10hLRGz4zvrpFpKDsFkMRa1aTBw16qigxu/NKb8bCZVpukjXa6mzBOjhNVjuBlJ0 0WvWjm6yBKd17eZ4KJhAVq5f9Z1BA5hh4a/MTu8UBlNkd8wQrcD7rMcJquoNMgHlnAhb kOZc78Ynj26kMJAEIA0T1HAvhaq7OejzniMAxfDZasqeRN0iB0YOitw3MlaUcdkNirku 9LDS6BQvdSOcgxT5rwG42RwE26/4TBJxAVO67pbOrYkZmULDziV/7VX+zpJw3q/hnnvU G1nA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=/HZISRTpvYHYIp98Z09QG9oWLbCtF0AHFib4N/wAOUY=; b=ntBPhWuCcxETulK+3L4yDTIEEK5BWt/32kfIXiNJYwXLf6Q51X6K4gXf35ypSkJXag SSe+v6/alZUeaNMfECgtErvJ8CO6AUpiWtjxWL2COQErfC8TQEsNqyo2LqaugW2Wd9rt ux+yam+kxDRD9hLy2RiQZWF/nvIcpy4XGpHMsDsRS1SrW+t1RbU3LM265FADLpIr/1U+ loW8/GhfdMPXbpI/N5ippd5AAqQpiVEqhP3WJMdEvZPE1jkHIMTZ6DOkCz0wvexZLhfD g9mte9Bp9tYfL/7Cn18NCMJGlDAUoPPw/RnBEYfm2CRJ+iVqJt2/7Nk/CcrMLFg6n6CR C1ew== X-Gm-Message-State: AFeK/H1XRjlNkiGhj8SGv9+Jmf7CSvDW9rtzpV1gScbNjjDqh24kEpEPHAoped1zu1WP4Uyh X-Received: by 10.84.174.131 with SMTP id r3mr71966452plb.136.1491868173743; Mon, 10 Apr 2017 16:49:33 -0700 (PDT) Received: from roshar.mtv.corp.google.com ([100.96.238.26]) by smtp.gmail.com with ESMTPSA id x204sm26225132pgx.63.2017.04.10.16.49.32 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 10 Apr 2017 16:49:32 -0700 (PDT) From: Brandon Williams To: git@vger.kernel.org Cc: Brandon Williams Subject: [PATCH 5/5] run-command: add note about forking and threading Date: Mon, 10 Apr 2017 16:49:19 -0700 Message-Id: <20170410234919.34586-6-bmwill@google.com> X-Mailer: git-send-email 2.12.2.715.g7642488e1d-goog In-Reply-To: <20170410234919.34586-1-bmwill@google.com> References: <20170410234919.34586-1-bmwill@google.com> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Allocation was pushed before forking in order to avoid potential deadlocking when forking while multiple threads are running. This deadlocking is possible when a thread (other than the one forking) has acquired a lock and didn't get around to releasing it before the fork. This leaves the lock in a locked state in the resulting process with no hope of it ever being released. Signed-off-by: Brandon Williams --- run-command.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/run-command.c b/run-command.c index 84c63b209..2b3249de4 100644 --- a/run-command.c +++ b/run-command.c @@ -458,6 +458,14 @@ int start_command(struct child_process *cmd) argv_array_pushv(&argv, cmd->argv); } + /* + * NOTE: In order to prevent deadlocking when using threads special + * care should be taken with the function calls made in between the + * fork() and exec() calls. No calls should be made to functions which + * require acquiring a lock (e.g. malloc) as the lock could have been + * held by another thread at the time of forking, causing the lock to + * never be released in the child process. + */ cmd->pid = fork(); failed_errno = errno; if (!cmd->pid) { -- 2.12.2.715.g7642488e1d-goog