From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: Re: perf: remount of tracefs required Date: Tue, 4 Aug 2015 12:27:46 -0300 Message-ID: <20150804152746.GA3126@kernel.org> References: <5297956.5blcApkzlY@milian-kdab2> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail.kernel.org ([198.145.29.136]:44882 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753315AbbHDP1s (ORCPT ); Tue, 4 Aug 2015 11:27:48 -0400 Content-Disposition: inline In-Reply-To: <5297956.5blcApkzlY@milian-kdab2> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Milian Wolff Cc: linux-perf-users@vger.kernel.org Em Tue, Aug 04, 2015 at 04:44:53PM +0200, Milian Wolff escreveu: > on ArchLinux with Linux 4.1.3, perf 4.1.0, I get: > > $ perf trace > Error: No permissions to read > /sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit) > Hint: Try 'sudo mount -o remount,mode=755 /sys/kernel/debug' > $ sudo mount -o remount,mode=755 /sys/kernel/debug > $ perf trace > Error: No permissions to read > /sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit) > Hint: Try 'sudo mount -o remount,mode=755 /sys/kernel/debug' > > This is b/c Arch uses tracefs, and running > > $ sudo mount -o remount,mode=755 /sys/kernel/debug/tracefs > > fixes the issue for me. Could someone please amend the error message? Do I > also need to remount debugfs, or is tracefs sufficient for using more advanced > perf tools? Well: [acme@zoo linux]$ perf trace ls Error: No permissions to read /sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit) Hint: Try 'sudo mount -o remount,mode=755 /sys/kernel/debug' [acme@zoo linux]$ ls -la /sys/kernel/debug ls: cannot open directory /sys/kernel/debug: Permission denied [acme@zoo linux]$ So, I can't access debugfs, that is where the canonical mount point for tracefs is, so the message can be read as well as: "hey, let me get to where tracefs is". Once that is done: [acme@zoo linux]$ sudo mount -o remount,mode=755 /sys/kernel/debug [sudo] password for acme: [acme@zoo linux]$ ls -la /sys/kernel/debug total 0 drwxr-xr-x. 32 root root 0 Aug 4 08:35 . drwxr-xr-x. 10 root root 0 Aug 4 08:35 .. drwxr-xr-x. 2 root root 0 Aug 4 08:35 acpi drwxr-xr-x. 2 root root 0 Aug 4 08:35 zswap [acme@zoo linux]$ ls -la /sys/kernel/debug/tracing/ ls: cannot open directory /sys/kernel/debug/tracing/: Permission denied [acme@zoo linux]$ So, if I try: [acme@zoo linux]$ trace usleep 1 Error: No permissions to read /sys/kernel/debug/tracing/events/raw_syscalls/sys_(enter|exit) Hint: Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing' [acme@zoo linux]$ It asks for that same remount to be done, this time for tracefs, once that is done: [acme@zoo linux]$ sudo mount -o remount,mode=755 /sys/kernel/debug/tracing [acme@zoo linux]$ trace usleep 1 0.086 (0.001 ms): usleep/10122 brk( ) = 0x556309717000 0.101 (0.003 ms): usleep/10122 mmap(len: 4096, prot: READ|WRITE, flags: PRIVATE|ANONYMOUS, fd: -1) = 0x7f6f856ab000 [acme@zoo linux]$ It works. I guess what fixes what you report is this cset: commit ab85785aa13c36440a91a8e9f7616357de411a1f Author: Arnaldo Carvalho de Melo Date: Mon Jul 6 08:51:41 2015 -0300 tools lib api debugfs: Check for tracefs when reporting errors Now that we have two mountpoints, one for debugfs and another, for tracefs, we end up needing to check permissions for both, so, on a system with default config we were always asking the user to check the permission of the debugfs mountpoint, even when it was already sufficient. Fix it. ----------- [acme@zoo linux]$ git describe ab85785aa13c36440a91a8e9f7616357de411a1f v4.2-rc1-17-gab85785aa13c So, can you try running the perf tools, built from the latest 4.2-rc codebase to see if it behaves as you expect? - Arnaldo