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 16D2526A0E0; Tue, 8 Apr 2025 12:08:55 +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=1744114135; cv=none; b=lsBrexgNvxDs0iOxtl52AQHhLSa111ntY0kzss83MJImoH1UdT4Q7kbd/aTO9WczBhTLCwaGtA6m9fg8JLZ74uWdfPgOi8hbZg24GJvWLOVcq+TBrmC4QLdrS5//nwZVI9G5qlGmgrEfRQWQpIvbTTn6o1HzSbgzBjcXzd2tLOk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744114135; c=relaxed/simple; bh=fD5BxW6jgNmV+5NsRPNH6JbZyN8Zf1gmrI7rJb8T5jE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KcNOC67kC9pEcfkrunqlWUm9AMoyc5fdbLlHhb+Y2VY+z1J3wFzBOTNu0vBzAK0OU6sUn713Iy5S/jdKGIrEpLbuRD5IHf42gFdqtoR32Etnr2WxBqII2wRJ6xbKZB2gq9rZI7JRRGz2QvTyQ+TIHkZCevEt3PtjG8G1NQgRa20= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=KRjnAmY4; 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="KRjnAmY4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9902FC4CEE5; Tue, 8 Apr 2025 12:08:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1744114135; bh=fD5BxW6jgNmV+5NsRPNH6JbZyN8Zf1gmrI7rJb8T5jE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KRjnAmY4lz0ohJ+6es9hkqn5wto+9IF4Zflj0Pz5ib1+ZJ0LckIg0W3KlDOUr3nUY 028biXOVrH4jEJnHO3XjCvcileRYdAIPFROm1cfEUNf/d2GfybktGw0jW2Y/bpgw5N 2WZtVtbkFNcPyLxhOD3pJVd5knNHxmAk0Lm+k72Q= 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 5.4 148/154] x86/tsc: Always save/restore TSC sched_clock() on suspend/resume Date: Tue, 8 Apr 2025 12:51:29 +0200 Message-ID: <20250408104820.043863039@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250408104815.295196624@linuxfoundation.org> References: <20250408104815.295196624@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 5.4-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 @@ -912,7 +912,7 @@ 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(); @@ -932,7 +932,7 @@ 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);