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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 09522C54EAA for ; Mon, 30 Jan 2023 14:26:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237450AbjA3O0j (ORCPT ); Mon, 30 Jan 2023 09:26:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42042 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236658AbjA3O0R (ORCPT ); Mon, 30 Jan 2023 09:26:17 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8AD3A1BF7 for ; Mon, 30 Jan 2023 06:25:00 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 2EEB9B8117E for ; Mon, 30 Jan 2023 14:25:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 62C08C4339B; Mon, 30 Jan 2023 14:24:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1675088698; bh=tMi/I2IQP7Y1fVtCtwAubQHLyulTqFBBke+i7It+p7E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=BBL4rnals3FCtGIkTcQ/eh9kFtWNDrFmWjR+iGsTJPwMx4kJm3q/Qr5ZGqL0M6Krj nae+KKDVJY0b+E8BeDn6RqMAHnDXCoWaNZcCcvz73Y1zAY3sOiJ+8jUxBoOTrvZOsl LaejH++bOwU3WSuq8NkJW7XCwJy5xGj81WLHSHNI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Masami Hiramatsu , Mark Rutland , "Steven Rostedt (Google)" Subject: [PATCH 5.10 105/143] ftrace/scripts: Update the instructions for ftrace-bisect.sh Date: Mon, 30 Jan 2023 14:52:42 +0100 Message-Id: <20230130134311.189244854@linuxfoundation.org> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230130134306.862721518@linuxfoundation.org> References: <20230130134306.862721518@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Steven Rostedt (Google) commit 7ae4ba7195b1bac04a4210a499da9d8c63b0ba9c upstream. The instructions for the ftrace-bisect.sh script, which is used to find what function is being traced that is causing a kernel crash, and possibly a triple fault reboot, uses the old method. In 5.1, a new feature was added that let the user write in the index into available_filter_functions that maps to the function a user wants to set in set_ftrace_filter (or set_ftrace_notrace). This takes O(1) to set, as suppose to writing a function name, which takes O(n) (where n is the number of functions in available_filter_functions). The ftrace-bisect.sh requires setting half of the functions in available_filter_functions, which is O(n^2) using the name method to enable and can take several minutes to complete. The number method is O(n) which takes less than a second to complete. Using the number method for any kernel 5.1 and after is the proper way to do the bisect. Update the usage to reflect the new change, as well as using the /sys/kernel/tracing path instead of the obsolete debugfs path. Link: https://lkml.kernel.org/r/20230123112252.022003dd@gandalf.local.home Cc: stable@vger.kernel.org Cc: Masami Hiramatsu Acked-by: Mark Rutland Fixes: f79b3f338564e ("ftrace: Allow enabling of filters via index of available_filter_functions") Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman --- scripts/tracing/ftrace-bisect.sh | 34 ++++++++++++++++++++++++++-------- 1 file changed, 26 insertions(+), 8 deletions(-) --- a/scripts/tracing/ftrace-bisect.sh +++ b/scripts/tracing/ftrace-bisect.sh @@ -12,7 +12,7 @@ # (note, if this is a problem with function_graph tracing, then simply # replace "function" with "function_graph" in the following steps). # -# # cd /sys/kernel/debug/tracing +# # cd /sys/kernel/tracing # # echo schedule > set_ftrace_filter # # echo function > current_tracer # @@ -20,22 +20,40 @@ # # # echo nop > current_tracer # -# # cat available_filter_functions > ~/full-file +# Starting with v5.1 this can be done with numbers, making it much faster: +# +# The old (slow) way, for kernels before v5.1. +# +# [old-way] # cat available_filter_functions > ~/full-file +# +# [old-way] *** Note *** this process will take several minutes to update the +# [old-way] filters. Setting multiple functions is an O(n^2) operation, and we +# [old-way] are dealing with thousands of functions. So go have coffee, talk +# [old-way] with your coworkers, read facebook. And eventually, this operation +# [old-way] will end. +# +# The new way (using numbers) is an O(n) operation, and usually takes less than a second. +# +# seq `wc -l available_filter_functions | cut -d' ' -f1` > ~/full-file +# +# This will create a sequence of numbers that match the functions in +# available_filter_functions, and when echoing in a number into the +# set_ftrace_filter file, it will enable the corresponding function in +# O(1) time. Making enabling all functions O(n) where n is the number of +# functions to enable. +# +# For either the new or old way, the rest of the operations remain the same. +# # # ftrace-bisect ~/full-file ~/test-file ~/non-test-file # # cat ~/test-file > set_ftrace_filter # -# *** Note *** this will take several minutes. Setting multiple functions is -# an O(n^2) operation, and we are dealing with thousands of functions. So go -# have coffee, talk with your coworkers, read facebook. And eventually, this -# operation will end. -# # # echo function > current_tracer # # If it crashes, we know that ~/test-file has a bad function. # # Reboot back to test kernel. # -# # cd /sys/kernel/debug/tracing +# # cd /sys/kernel/tracing # # mv ~/test-file ~/full-file # # If it didn't crash.