user/sven/linux.git/include/linux/printk.h, branch v5.3.2

panic: avoid the extra noise dmesg

2019-05-15T02:52:51Z

When kernel panic happens, it will first print the panic call stack, then the ending msg like: [ 35.743249] ---[ end Kernel panic - not syncing: Fatal exception [ 35.749975] ------------[ cut here ]------------ The above message are very useful for debugging. But if system is configured to not reboot on panic, say the "panic_timeout" parameter equals 0, it will likely print out many noisy message like WARN() call stack for each and every CPU except the panic one, messages like below: WARNING: CPU: 1 PID: 280 at kernel/sched/core.c:1198 set_task_cpu+0x183/0x190 Call Trace: try_to_wake_up default_wake_function autoremove_wake_function __wake_up_common __wake_up_common_lock __wake_up wake_up_klogd_work_func irq_work_run_list irq_work_tick update_process_times tick_sched_timer __hrtimer_run_queues hrtimer_interrupt smp_apic_timer_interrupt apic_timer_interrupt For people working in console mode, the screen will first show the panic call stack, but immediately overridden by these noisy extra messages, which makes debugging much more difficult, as the original context gets lost on screen. Also these noisy messages will confuse some users, as I have seen many bug reporters posted the noisy message into bugzilla, instead of the real panic call stack and context. Adding a flag "suppress_printk" which gets set in panic() to avoid those noisy messages, without changing current kernel behavior that both panic blinking and sysrq magic key can work as is, suggested by Petr Mladek. To verify this, make sure kernel is not configured to reboot on panic and in console # echo c > /proc/sysrq-trigger to see if console only prints out the panic call stack. Link: http://lkml.kernel.org/r/1551430186-24169-1-git-send-email-feng.tang@intel.com Signed-off-by: Feng Tang Suggested-by: Petr Mladek Reviewed-by: Petr Mladek Acked-by: Steven Rostedt (VMware) Acked-by: Sergey Senozhatsky Cc: Thomas Gleixner Cc: Kees Cook Cc: Borislav Petkov Cc: Andi Kleen Cc: Peter Zijlstra Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: Sasha Levin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

printk: Tie printk_once / printk_deferred_once into .data.once for reset

2019-04-15T08:23:53Z

In commit b1fca27d384e ("kernel debug: support resetting WARN*_ONCE") we got the opportunity to reset state on the one shot messages, without having to reboot. However printk_once (printk_deferred_once) live in a different file and didn't get the same kind of update/conversion, so they remain unconditionally one shot, until the system is rebooted. For example, we currently have: sched/rt.c: printk_deferred_once("sched: RT throttling activated\n"); ..which could reasonably be tripped as someone is testing and tuning a new system/workload and their task placements. For consistency, and to avoid reboots in the same vein as the original commit, we make these two instances of _once the same as the WARN*_ONCE instances are. Link: http://lkml.kernel.org/r/1555121491-31213-1-git-send-email-paul.gortmaker@windriver.com Cc: Andi Kleen Cc: Petr Mladek Cc: Sergey Senozhatsky Cc: Steven Rostedt Cc: Andrew Morton Signed-off-by: Paul Gortmaker Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek

Merge tag 'printk-for-5.1' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk

2019-03-09T17:22:42Z

Pull printk updates from Petr Mladek: - Allow to sort mixed lines by an extra information about the caller - Remove no longer used LOG_PREFIX. - Some clean up and documentation update. * tag 'printk-for-5.1' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk: printk/docs: Add extra integer types to printk-formats printk: Remove no longer used LOG_PREFIX. lib/vsprintf: Remove %pCr remnant in comment printk: Pass caller information to log_store(). printk: Add caller information to printk() output.

linux/printk.h: use DYNAMIC_DEBUG_BRANCH in pr_debug_ratelimited

2019-03-08T02:32:00Z

pr_debug_ratelimited tests the dynamic debug descriptor the old-fashioned way, and doesn't utilize the static key/jump label implementation when CONFIG_JUMP_LABEL is set. Use the DYNAMIC_DEBUG_BRANCH which is defined appropriately. Link: http://lkml.kernel.org/r/20190212214150.4807-4-linux@rasmusvillemoes.dk Signed-off-by: Rasmus Villemoes Acked-by: Petr Mladek Acked-by: Jason Baron Cc: Steven Rostedt Cc: David Sterba Cc: Greg Kroah-Hartman Cc: Ingo Molnar Cc: "Rafael J . Wysocki" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

printk: Remove no longer used LOG_PREFIX.

2019-03-04T12:42:05Z

When commit 5becfb1df5ac8e49 ("kmsg: merge continuation records while printing") introduced LOG_PREFIX, we used KERN_DEFAULT etc. as a flag for setting LOG_PREFIX in order to tell whether to call cont_add() (i.e. whether to append the message to "struct cont"). But since commit 4bcc595ccd80decb ("printk: reinstate KERN_CONT for printing continuation lines") inverted the behavior (i.e. don't append the message to "struct cont" unless KERN_CONT is specified) and commit 5aa068ea4082b39e ("printk: remove games with previous record flags") removed the last LOG_PREFIX check, setting LOG_PREFIX via KERN_DEFAULT etc. is no longer meaningful. Therefore, we can remove LOG_PREFIX and make KERN_DEFAULT empty string. Link: http://lkml.kernel.org/r/1550829580-9189-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp To: Steven Rostedt To: Linus Torvalds Cc: linux-kernel@vger.kernel.org Cc: Tetsuo Handa Signed-off-by: Tetsuo Handa Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek

include/linux/printk.h: drop silly "static inline asmlinkage" from dump_stack()

2019-01-04T21:13:46Z

Empty function will be inlined so asmlinkage doesn't do anything. Link: http://lkml.kernel.org/r/20181124093530.GE10969@avx2 Signed-off-by: Alexey Dobriyan Reviewed-by: Andrew Morton Acked-by: Joey Pabalinas Cc: Petr Mladek Cc: Sergey Senozhatsky Cc: Steven Rostedt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

printk: Make printk_emit() local function.

2018-11-29T09:59:40Z

printk_emit() is called from only devkmsg_write() in the same file. Save object size by making it a local function. Link: http://lkml.kernel.org/r/5cc99d2c-c408-34f7-d1fc-e1cd2a9e31da@i-love.sakura.ne.jp Cc: Steven Rostedt Signed-off-by: Tetsuo Handa Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek

Merge branch 'for-4.19-nmi' into for-linus

2018-08-14T11:36:15Z

printk/nmi: Prevent deadlock when accessing the main log buffer in NMI

2018-07-09T12:10:40Z

The commit 719f6a7040f1bdaf96 ("printk: Use the main logbuf in NMI when logbuf_lock is available") brought back the possible deadlocks in printk() and NMI. The check of logbuf_lock is done only in printk_nmi_enter() to prevent mixed output. But another CPU might take the lock later, enter NMI, and: + Both NMIs might be serialized by yet another lock, for example, the one in nmi_cpu_backtrace(). + The other CPU might get stopped in NMI, see smp_send_stop() in panic(). The only safe solution is to use trylock when storing the message into the main log-buffer. It might cause reordering when some lines go to the main lock buffer directly and others are delayed via the per-CPU buffer. It means that it is not useful in general. This patch replaces the problematic NMI deferred context with NMI direct context. It can be used to mark a code that might produce many messages in NMI and the risk of losing them is more critical than problems with eventual reordering. The context is then used when dumping trace buffers on oops. It was the primary motivation for the original fix. Also the reordering is even smaller issue there because some traces have their own time stamps. Finally, nmi_cpu_backtrace() need not longer be serialized because it will always us the per-CPU buffers again. Fixes: 719f6a7040f1bdaf96 ("printk: Use the main logbuf in NMI when logbuf_lock is available") Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/20180627142028.11259-1-pmladek@suse.com To: Steven Rostedt Cc: Peter Zijlstra Cc: Tetsuo Handa Cc: Sergey Senozhatsky Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Acked-by: Sergey Senozhatsky Signed-off-by: Petr Mladek

printk: Make CONSOLE_LOGLEVEL_QUIET configurable

2018-06-27T14:14:29Z

The goal of passing the "quiet" option to the kernel is for the kernel to be quiet unless something really is wrong. Sofar passing quiet has been (mostly) equivalent to passing loglevel=4 on the kernel commandline. Which means to show any messages with a level of KERN_ERR or higher severity on the console. In practice this often does not result in a quiet boot though, since there are many false-positive or otherwise harmless error messages printed, defeating the purpose of the quiet option. Esp. the ACPICA code is really bad wrt this, but there are plenty of others too. This commit makes CONSOLE_LOGLEVEL_QUIET configurable. This for example will allow distros which want quiet to really mean quiet to set CONSOLE_LOGLEVEL_QUIET so that only messages with a higher severity then KERN_ERR (CRIT, ALERT, EMERG) get printed, avoiding an endless game of whack-a-mole silencing harmless error messages. Link: http://lkml.kernel.org/r/20180619115726.3098-1-hdegoede@redhat.com To: Petr Mladek To: Sergey Senozhatsky Cc: Hans de Goede Cc: Steven Rostedt Cc: linux-kernel@vger.kernel.org Signed-off-by: Hans de Goede Acked-by: Steven Rostedt (VMware) Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek