From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0A91524729E; Tue, 29 Apr 2025 17:34:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745948082; cv=none; b=AcPVJzL7zWA4BhRB+eNgA+m7Y9VrQLoOjKRnd36L2J8QOjencXcQnaiSCW9UkyH9JhpDKFIiAWKJ4obd9+Wmt+ZAR++XwPSG5JjLkvRcSRh+CWxRdiMpX0U7GZFFMiyrCbT5YPQl72fdCMddxapl3ZbkLkZOlgFpwZ2cQfaEw7I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745948082; c=relaxed/simple; bh=TEfCvMM0grEnEoOtMP6EEUOfbHhBYNENUDZKs9AfQs8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ZWl9A0hvvCa0NdmTKz66iBFfHaIMz5AIJNWWV8d9zxlFwwptcgdZNzi6qwkb5U82HD2cRLUzG0y26AG1k2TBODOE7GptryCfpHZ0OzNlagZzdfUBM5jBe68T8tJ0hE7JzvtC2BheOiYR4ajdw2qg/i+pxX2ovpRCiyDVTz/BWC0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=nVbpbjRE; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="nVbpbjRE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 52DF8C4CEE3; Tue, 29 Apr 2025 17:34:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1745948081; bh=TEfCvMM0grEnEoOtMP6EEUOfbHhBYNENUDZKs9AfQs8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nVbpbjREWhEEhYnK/HCAJO+p+PASXe6NtyofK78Aw790/G1nYNLrdMEkI6b51jqAs vm28nbrFK7cCWKET4bcfkcZaCBYQPazMYWZ5BmE+ZuQFWqmzzhAG2iiyy9dDrdK3qq zH8ZwKSQS9nIRGr41PzZX6sSGYh+sSSa/S3qK1iM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Benjamin Berg , Johannes Berg , Sasha Levin Subject: [PATCH 6.12 186/280] um: work around sched_yield not yielding in time-travel mode Date: Tue, 29 Apr 2025 18:42:07 +0200 Message-ID: <20250429161122.718302896@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250429161115.008747050@linuxfoundation.org> References: <20250429161115.008747050@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ 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