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 A731019AD5C; Tue, 8 Apr 2025 11:37:09 +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=1744112229; cv=none; b=Y/3A03wdmoTdlzP2u6Vu/G2R+vpwWVnE1MrM0TqBZAxLkF/JJnbMOzGiojk5gtZ38DyPET2fOsSazMuvVC8JSZZhXolvlV0hbwtrm40JoRvVhVMBZ33kg3kzYu3Y5oZqM7XXV1AeDa/biF1KE0KAcmhdxI4+49pHBIwn++xatwA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744112229; c=relaxed/simple; bh=Cs1jexvI6lcOlCSQET2+O6xwZQuIUZ4vWAzcrP2E02A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=f4LZRT+TUsUkFrOVPKGTqilv59CPbZXJbXuihWKhOPfPHt3imOctiHscwJ8C+JhF15eAcDKmzt+LNRzvZ4fit5GuwYv9gWQcGgkGlkus2t7K8ntvl+vEhbAezR5iKK1k/2VtU6oqj2Uam9tMhuGpehBb8XtvBegIwTDOQ9LQMuU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ohZK/cXi; 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="ohZK/cXi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 35907C4CEE5; Tue, 8 Apr 2025 11:37:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1744112229; bh=Cs1jexvI6lcOlCSQET2+O6xwZQuIUZ4vWAzcrP2E02A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ohZK/cXiRbIiZLztVG92umSEhj2waLPKRZv/rdGUEiaQFdc7sbzYMS8je8X81hAhu aL1XDqB+KPhoHoCT/ue2cDY94jqIGHcA2mjDcWgAWKwsRQ3qZVPD6TulxPoxf9qzio 7rxgIko0EzfYfLp68ufVcIUSs980l2a2sA9sIb3U= 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 6.14 683/731] x86/tsc: Always save/restore TSC sched_clock() on suspend/resume Date: Tue, 8 Apr 2025 12:49:40 +0200 Message-ID: <20250408104930.154393673@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250408104914.247897328@linuxfoundation.org> References: <20250408104914.247897328@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 6.14-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 @@ -959,7 +959,7 @@ 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(); @@ -979,7 +979,7 @@ 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);