From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C2946FC6196 for ; Wed, 6 Nov 2019 23:08:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9875120869 for ; Wed, 6 Nov 2019 23:08:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732898AbfKFXIc (ORCPT ); Wed, 6 Nov 2019 18:08:32 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:45579 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732877AbfKFXIa (ORCPT ); Wed, 6 Nov 2019 18:08:30 -0500 Received: from localhost ([127.0.0.1] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1iSUPa-0004lM-UP; Thu, 07 Nov 2019 00:08:27 +0100 Message-Id: <20191106224556.935606117@linutronix.de> User-Agent: quilt/0.65 Date: Wed, 06 Nov 2019 22:55:45 +0100 From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Ingo Molnar , Darren Hart , Yi Wang , Yang Tao , Oleg Nesterov , Florian Weimer , Carlos O'Donell , Alexander Viro Subject: [patch 11/12] futex: Provide distinct return value when owner is exiting References: <20191106215534.241796846@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org attach_to_pi_owner() returns -EAGAIN for various cases: - Owner task is exiting - Futex value has changed The caller drops the held locks (hash bucket, mmap_sem) and retries the operation. In case of the owner task exiting this can result in a live lock. As a preparatory step for seperating those cases, provide a distinct return value (EBUSY) for the owner exiting case. No funcitonal change. Signed-off-by: Thomas Gleixner --- kernel/futex.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1182,11 +1182,11 @@ static int handle_exit_race(u32 __user * u32 uval2; /* - * If the futex exit state is not yet FUTEX_STATE_DEAD, wait - * for it to finish. + * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the + * caller that the alleged owner is busy. */ if (tsk && tsk->futex_state != FUTEX_STATE_DEAD) - return -EAGAIN; + return -EBUSY; /* * Reread the user space value to handle the following situation: @@ -2092,12 +2092,13 @@ static int futex_requeue(u32 __user *uad if (!ret) goto retry; goto out; + case -EBUSY: case -EAGAIN: /* * Two reasons for this: - * - Owner is exiting and we just wait for the + * - EBUSY: Owner is exiting and we just wait for the * exit to complete. - * - The user space value changed. + * - EAGAIN: The user space value changed. */ double_unlock_hb(hb1, hb2); hb_waiters_dec(hb2); @@ -2843,12 +2844,13 @@ static int futex_lock_pi(u32 __user *uad goto out_unlock_put_key; case -EFAULT: goto uaddr_faulted; + case -EBUSY: case -EAGAIN: /* * Two reasons for this: - * - Task is exiting and we just wait for the + * - EBUSY: Task is exiting and we just wait for the * exit to complete. - * - The user space value changed. + * - EAGAIN: The user space value changed. */ queue_unlock(hb); put_futex_key(&q.key);