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 0E106264FB0; Tue, 8 Apr 2025 11:49:21 +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=1744112962; cv=none; b=bzZUWMNIitbZa4/I/QWY80P95jogFbIu4oy00e2TxY/2GeW6dkiJQ179yZ2Q8I7YpmLO/c/vyM/UuQa+w2ElOsjDQ2b5lyE1ONgdoQJbI9wN+cGkPuZlEf8NVJ6Lhlt5bedLyLT4Enw3BlON+NA+NzNjkDh6tpBzJH85va8xgh4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744112962; c=relaxed/simple; bh=NIGOCjrPsA3i/XWHbBomQVZ1/3UarDoTxGc9J4BMioo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=CBzzyjgEqyGSDOt4I5Ax0mJUgZ49pC5JXY31+hoKOqMfqeJP81s+exZksJuLqkcLjFjwX6iJpsRDbT8Wc+Ng1poK4F9/cMFMilAS63C7p+vAiHXdvKHC4fzWnnV/wV3gA3zyXdcMhuF/hQILlJN7iXoIXkiB7YtDNkryiArDa5U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=g9vwaNX/; 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="g9vwaNX/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0BAFFC4CEE5; Tue, 8 Apr 2025 11:49:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1744112961; bh=NIGOCjrPsA3i/XWHbBomQVZ1/3UarDoTxGc9J4BMioo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=g9vwaNX/Jb6KZk4UZg75wRp972BvGh5uqNsIxjCncXf0ypsJKV/wjiMXdAAGqw166 q4Qgap9GxXX3oB3LD5SM+Vga8U4qGLqwv7MLOP4FEdPS+S++586syGIOMUwFrupKSE NlrPERe08VQ+TxzBKi1lyVfaavUkb09TX1XmGYIQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Guilherme G. Piccoli" , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Linus Torvalds , Thadeu Lima de Souza Cascardo Subject: [PATCH 5.15 263/279] x86/tsc: Always save/restore TSC sched_clock() on suspend/resume Date: Tue, 8 Apr 2025 12:50:46 +0200 Message-ID: <20250408104833.486185037@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250408104826.319283234@linuxfoundation.org> References: <20250408104826.319283234@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 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Guilherme G. Piccoli commit d90c9de9de2f1712df56de6e4f7d6982d358cabe upstream. TSC could be reset in deep ACPI sleep states, even with invariant TSC. That's the reason we have sched_clock() save/restore functions, to deal with this situation. But what happens is that such functions are guarded with a check for the stability of sched_clock - if not considered stable, the save/restore routines aren't executed. On top of that, we have a clear comment in native_sched_clock() saying that *even* with TSC unstable, we continue using TSC for sched_clock due to its speed. In other words, if we have a situation of TSC getting detected as unstable, it marks the sched_clock as unstable as well, so subsequent S3 sleep cycles could bring bogus sched_clock values due to the lack of the save/restore mechanism, causing warnings like this: [22.954918] ------------[ cut here ]------------ [22.954923] Delta way too big! 18446743750843854390 ts=18446744072977390405 before=322133536015 after=322133536015 write stamp=18446744072977390405 [22.954923] If you just came from a suspend/resume, [22.954923] please switch to the trace global clock: [22.954923] echo global > /sys/kernel/tracing/trace_clock [22.954923] or add trace_clock=global to the kernel command line [22.954937] WARNING: CPU: 2 PID: 5728 at kernel/trace/ring_buffer.c:2890 rb_add_timestamp+0x193/0x1c0 Notice that the above was reproduced even with "trace_clock=global". The fix for that is to _always_ save/restore the sched_clock on suspend cycle _if TSC is used_ as sched_clock - only if we fallback to jiffies the sched_clock_stable() check becomes relevant to save/restore the sched_clock. Debugged-by: Thadeu Lima de Souza Cascardo Signed-off-by: Guilherme G. Piccoli Signed-off-by: Ingo Molnar Cc: stable@vger.kernel.org Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250215210314.351480-1-gpiccoli@igalia.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/tsc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -920,7 +920,7 @@ static unsigned long long cyc2ns_suspend void tsc_save_sched_clock_state(void) { - if (!sched_clock_stable()) + if (!static_branch_likely(&__use_tsc) && !sched_clock_stable()) return; cyc2ns_suspend = sched_clock(); @@ -940,7 +940,7 @@ void tsc_restore_sched_clock_state(void) unsigned long flags; int cpu; - if (!sched_clock_stable()) + if (!static_branch_likely(&__use_tsc) && !sched_clock_stable()) return; local_irq_save(flags);