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Mon, 11 Nov 2019 18:17:50 -0800 (PST) Date: Tue, 12 Nov 2019 11:17:47 +0900 From: Sergey Senozhatsky To: Dmitry Safonov Subject: Re: [PATCH 00/50] Add log level to show_stack() Message-ID: <20191112021747.GA68506@google.com> References: <20191106030542.868541-1-dima@arista.com> <20191106083538.z5nlpuf64cigxigh@pathway.suse.cz> <20191108103719.GB175344@google.com> <20191108130447.h3wfgo4efjkto56f@pathway.suse.cz> <20191111012336.GA85185@google.com> <13e72b62-c842-8ed5-5b41-bc1692b28f53@arista.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <13e72b62-c842-8ed5-5b41-bc1692b28f53@arista.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191111_181754_920050_FC5DE91F X-CRM114-Status: GOOD ( 16.49 ) X-BeenThere: linux-snps-arc@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on Synopsys ARC Processors List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juri Lelli , Sergey Senozhatsky , linux-sh@vger.kernel.org, Catalin Marinas , Ben Segall , Guo Ren , Pavel Machek , Vincent Guittot , Paul Burton , Michael Ellerman , Geert Uytterhoeven , Mel Gorman , Jiri Slaby , Matt Turner , uclinux-h8-devel@lists.sourceforge.jp, Petr Mladek , linux-pm@vger.kernel.org, Heiko Carstens , linux-um@lists.infradead.org, Thomas Gleixner , Dietmar Eggemann , Richard Henderson , Greg Kroah-Hartman , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, Ralf Baechle , Paul Mackerras , Andrew Morton , linux-ia64@vger.kernel.org, Tetsuo Handa , James Hogan , "James E.J. Bottomley" , Max Filippov , Vincent Chen , Ingo Molnar , linux-s390@vger.kernel.org, linux-c6x-dev@linux-c6x.org, Yoshinori Sato , linux-hexagon@vger.kernel.org, Helge Deller , linux-xtensa@linux-xtensa.org, Vasily Gorbik , Aurelien Jacquiot , linux-m68k@lists.linux-m68k.org, Stafford Horne , linux-arm-kernel@lists.infradead.org, Chris Zankel , Tony Luck , Douglas Anderson , Benjamin Herrenschmidt , Dmitry Safonov <0x7f454c46@gmail.com>, Will Deacon , Daniel Thompson , Brian Cain , Christian Borntraeger , kgdb-bugreport@lists.sourceforge.net, linux-snps-arc@lists.infradead.org, Fenghua Yu , Borislav Petkov , Jeff Dike , Steven Rostedt , Ivan Kokshaysky , Greentime Hu , Guan Xuetao , linux-parisc@vger.kernel.org, linux-alpha@vger.kernel.org, Ley Foon Tan , "David S. Miller" , Rich Felker , Len Brown , Peter Zijlstra , "H. Peter Anvin" , sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org, Anton Ivanov , Jonas Bonn , Richard Weinberger , x86@kernel.org, Russell King , clang-built-linux@googlegroups.com, Ingo Molnar , Mark Salter , Albert Ou , Stefan Kristiansson , openrisc@lists.librecores.org, Paul Walmsley , Michal Simek , Vineet Gupta , linux-mips@vger.kernel.org, Sergey Senozhatsky , Palmer Dabbelt , Jason Wessel , nios2-dev@lists.rocketboards.org, linuxppc-dev@lists.ozlabs.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-snps-arc" Errors-To: linux-snps-arc-bounces+linux-snps-arc=archiver.kernel.org@lists.infradead.org On (19/11/11 19:47), Dmitry Safonov wrote: [..] > I don't see how bits on task_struct or in per-cpu are easier than > supplying a log level parameter down the stack. > How would it work if sysrq_handle_crash() called by key-press? > How would that interact with deferred printing? > How would it make visible prints from current context, but not from > something that preempted it? [..] per-context log_level works pretty much the same way as per-message log_level. // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - // static DEFINE_PER_CPU(int, cpu_loglevels[4]); // @INITME.. LOGLEVEL_DEBUG + 1? static int __printing_context(void) { unsigned int preempt = preempt_count(); if (!(preempt & (NMI_MASK | HARDIRQ_MASK | SOFITRQ_OFFSET))) return 0; if (preempt & SOFITRQ_OFFSET) return 1; if (preempt & HARDIRQ_MASK) return 2; return 3; } static int adj_context_loglevel(int level) { int ctx = __printing_context(); int cpu_level = this_cpu_read(cpu_loglevels[ctx]); // this one is important if (level == LOGLEVEL_SCHED) return level; // we are not in emergency context if (cpu_level == LOGLEVEL_DEBUG + 1) return level; // we better not override these if (LOGLEVEL_EMERG <= level && level <= LOGLEVEL_ERR) return level; return cpu_level; } void printk_emergency_enter(int log_level) { int ctx; preempt_disable(); ctx = __printing_context(); this_cpu_write(cpu_loglevels[ctx], log_level); } void printk_emergency_exit(void) { int ctx = __printing_context(); this_cpu_write(cpu_loglevels[ctx], LOGLEVEL_DEBUG + 1); preempt_enable(); } void vprintk_emit(...) { level = adj_context_loglevel(level); } // // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - // // static void __show_stack(struct task_struct *task, unsigned long *sp) { printk(); ... printk(); } void show_stack(struct task_struct *task, unsigned long *sp, int log_level) { printk_emergency_enter(log_level); __show_stack(task, sp); printk_emergency_exit(); } // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - // show_stack() never schedules, disabling preemption around it should not change anything. Should it be interrupted, we will handle it via preempt count. printk_emergency_enter(log_level) handles every printk() that __show_stack() and friends do. Not worse than printk("%s Stack", lvl); all over the place. > What I'm going to do - is to fix all build and reported issues, I'll > send v2 this week and feel free to NAK it, I will forget about those > patches and won't be offended. Lovely. And - no, I'm not going to NAK platform specific changes. Just so you know. *All* I'm talking about is an alternative, less "go and touch a ton of platform code" approach. The argument "I patched so many files that I'm not even going to discuss anything now" is not productive, to say the least. Hope this clarifies. -ss _______________________________________________ linux-snps-arc mailing list linux-snps-arc@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-snps-arc