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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 C0657C32750 for ; Fri, 2 Aug 2019 13:25:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 97BEC20644 for ; Fri, 2 Aug 2019 13:25:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564752347; bh=tgE9qEUA0xbKx/2XjegxyGqUS9aJV2GgF602hqiccm0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=fFaZkPdiujvQTykfccvSwxylvwuxmEdKh7ov7GQPYG4b6KjzphsddsfMUJOkxI06b rgktNsEuuBRohX3mNFccAw4PyqNsevmPC5xJK6zJsKPV561b86XZjwEKjeNQ3iR66x 3PSzsMIT/gVxlzJQy8UYGyydOkVU15t4gBOE8lcA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394419AbfHBNZq (ORCPT ); Fri, 2 Aug 2019 09:25:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:36392 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2394406AbfHBNZn (ORCPT ); Fri, 2 Aug 2019 09:25:43 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2B75721851; Fri, 2 Aug 2019 13:25:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564752342; bh=tgE9qEUA0xbKx/2XjegxyGqUS9aJV2GgF602hqiccm0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RYBdn5V8JS/d3vtdbOTfWgd/j6gRYpkTI+ViMWnWdZqgzc+YpPj1HP2ReOEKFrU/L dlxuGxiX9fuvbMl5apGhENJ4baw1wp40QLgrph7nI8ZsaZu715mmaxU14wGrOIJjjU Sy9pbrjBPq9IergSKS2k+20uFCtndcClVVNP7Sn8= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Peter Zijlstra , Will Deacon , Linus Torvalds , Peter Hurley , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH AUTOSEL 4.14 29/30] tty/ldsem, locking/rwsem: Add missing ACQUIRE to read_failed sleep loop Date: Fri, 2 Aug 2019 09:24:21 -0400 Message-Id: <20190802132422.13963-29-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190802132422.13963-1-sashal@kernel.org> References: <20190802132422.13963-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra [ Upstream commit 952041a8639a7a3a73a2b6573cb8aa8518bc39f8 ] While reviewing rwsem down_slowpath, Will noticed ldsem had a copy of a bug we just found for rwsem. X = 0; CPU0 CPU1 rwsem_down_read() for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); X = 1; rwsem_up_write(); rwsem_mark_wake() atomic_long_add(adjustment, &sem->count); smp_store_release(&waiter->task, NULL); if (!waiter.task) break; ... } r = X; Allows 'r == 0'. Reported-by: Will Deacon Signed-off-by: Peter Zijlstra (Intel) Acked-by: Will Deacon Cc: Linus Torvalds Cc: Peter Hurley Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 4898e640caf0 ("tty: Add timed, writer-prioritized rw semaphore") Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin --- drivers/tty/tty_ldsem.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index 5c2cec298816b..c6ce34161281a 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -139,8 +139,7 @@ static void __ldsem_wake_readers(struct ld_semaphore *sem) list_for_each_entry_safe(waiter, next, &sem->read_wait, list) { tsk = waiter->task; - smp_mb(); - waiter->task = NULL; + smp_store_release(&waiter->task, NULL); wake_up_process(tsk); put_task_struct(tsk); } @@ -235,7 +234,7 @@ down_read_failed(struct ld_semaphore *sem, long count, long timeout) for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); - if (!waiter.task) + if (!smp_load_acquire(&waiter.task)) break; if (!timeout) break; -- 2.20.1