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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C25E9C369A6 for ; Mon, 7 Apr 2025 21:46:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=iI4bH/HSRPcYTotIIE5PQ35iIB8Ii1vOuyCkkepPDvU=; b=q10iy5qVpbG482h/HAu9xqw6Cq +Q8oXsC7UsA4CwYdMK/voj2SOWkDHhogO/1qAg9dNmlqP4C4ViswgF/vnGqwjvoiXSDdYubn0E1XX admQ9ZdPZU11WbBI6Nhn4LxbzWCOSMh73/ZABxhs8nO3g086GwzP2UzLKiup4rIzWl9vux87kcYIC Bl66Jaw/4p5sCelFoqmT6Cgi5DqHVFtgnZt5+5BNAm42HKOQXtbwPSXP239qVAd9Hlj/nCwSH7ty0 CReKOUxjENpSMUA5HsGWfmRLLGLbLtFD2C88mt0ZLQUq40TEEsKk38o0YVUTNyzAnD3gRoGvI+D+0 soKw07Cw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.1 #2 (Red Hat Linux)) id 1u1uIk-0000000240f-3yO1; Mon, 07 Apr 2025 21:46:42 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.98.1 #2 (Red Hat Linux)) id 1u1qwo-00000001U3T-2T6o for linux-um@lists.infradead.org; Mon, 07 Apr 2025 18:11:51 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id C81795C5557; Mon, 7 Apr 2025 18:09:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 831C4C4CEDD; Mon, 7 Apr 2025 18:11:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744049509; bh=uQ9BX1Anrr185nCbF9o0UfRIAVFd3yOMLRqLKUlV05E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=LpAnxmvV1vsUpz/fpBuGnvMm5CPHxwy0/lnaZaJzXQYi1lZJm9qo02mmQPNuDMMGR vsqN07xtFMPtfVD/FK/NKXwaUQrXVa9lhzUVJBcHmsQ4ky3UJUpgtnpvkcEmtwU2IL mc0aZDB9KLNW2u4J359MP/Zn5VFB3GuHzzL7NR+aQJp9w9UF8TJOoVwZQPlHWTsPke RcvZN9IbU2sVahkhZPeA/NJqIHkScD1GW+Hov6YahLpswjG9WSgdd2VwKtzGe2zODL lHQhJl5YVEbLvX4LG+oAlXHQzoxjmIU1FVDkMDEnb3PltWPc4iPPHMKPgq03UZVsni rM87VHO6H4ZAQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Benjamin Berg , Johannes Berg , Sasha Levin , richard@nod.at, anton.ivanov@cambridgegreys.com, johannes@sipsolutions.net, linux-um@lists.infradead.org Subject: [PATCH AUTOSEL 6.14 23/31] um: work around sched_yield not yielding in time-travel mode Date: Mon, 7 Apr 2025 14:10:39 -0400 Message-Id: <20250407181054.3177479-23-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250407181054.3177479-1-sashal@kernel.org> References: <20250407181054.3177479-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.14.1 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250407_111150_670063_676C75C8 X-CRM114-Status: GOOD ( 12.09 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org From: Benjamin Berg [ Upstream commit 887c5c12e80c8424bd471122d2e8b6b462e12874 ] sched_yield by a userspace may not actually cause scheduling in time-travel mode as no time has passed. In the case seen it appears to be a badly implemented userspace spinlock in ASAN. Unfortunately, with time-travel it causes an extreme slowdown or even deadlock depending on the kernel configuration (CONFIG_UML_MAX_USERSPACE_ITERATIONS). Work around it by accounting time to the process whenever it executes a sched_yield syscall. Signed-off-by: Benjamin Berg Link: https://patch.msgid.link/20250314130815.226872-1-benjamin@sipsolutions.net Signed-off-by: Johannes Berg Signed-off-by: Sasha Levin --- arch/um/include/linux/time-internal.h | 2 ++ arch/um/kernel/skas/syscall.c | 11 +++++++++++ 2 files changed, 13 insertions(+) diff --git a/arch/um/include/linux/time-internal.h b/arch/um/include/linux/time-internal.h index b22226634ff60..138908b999d76 100644 --- a/arch/um/include/linux/time-internal.h +++ b/arch/um/include/linux/time-internal.h @@ -83,6 +83,8 @@ extern void time_travel_not_configured(void); #define time_travel_del_event(...) time_travel_not_configured() #endif /* CONFIG_UML_TIME_TRAVEL_SUPPORT */ +extern unsigned long tt_extra_sched_jiffies; + /* * Without CONFIG_UML_TIME_TRAVEL_SUPPORT this is a linker error if used, * which is intentional since we really shouldn't link it in that case. diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c index b09e85279d2b8..a5beaea2967ec 100644 --- a/arch/um/kernel/skas/syscall.c +++ b/arch/um/kernel/skas/syscall.c @@ -31,6 +31,17 @@ void handle_syscall(struct uml_pt_regs *r) goto out; syscall = UPT_SYSCALL_NR(r); + + /* + * If no time passes, then sched_yield may not actually yield, causing + * broken spinlock implementations in userspace (ASAN) to hang for long + * periods of time. + */ + if ((time_travel_mode == TT_MODE_INFCPU || + time_travel_mode == TT_MODE_EXTERNAL) && + syscall == __NR_sched_yield) + tt_extra_sched_jiffies += 1; + if (syscall >= 0 && syscall < __NR_syscalls) { unsigned long ret = EXECUTE_SYSCALL(syscall, regs); -- 2.39.5