linux/kernel/printk, branch v4.11

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:36Z

We are going to split out of , which will have to be picked up from other headers and a couple of .c files. Create a trivial placeholder file that just maps to to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:34Z

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:27Z

We are going to split out of , which will have to be picked up from other headers and .c files. Create a trivial placeholder file that just maps to to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

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

2017-02-23T01:33:34Z

Pull printk updates from Petr Mladek: - Add Petr Mladek, Sergey Senozhatsky as printk maintainers, and Steven Rostedt as the printk reviewer. This idea came up after the discussion about printk issues at Kernel Summit. It was formulated and discussed at lkml[1]. - Extend a lock-less NMI per-cpu buffers idea to handle recursive printk() calls by Sergey Senozhatsky[2]. It is the first step in sanitizing printk as discussed at Kernel Summit. The change allows to see messages that would normally get ignored or would cause a deadlock. Also it allows to enable lockdep in printk(). This already paid off. The testing in linux-next helped to discover two old problems that were hidden before[3][4]. - Remove unused parameter by Sergey Senozhatsky. Clean up after a past change. [1] http://lkml.kernel.org/r/1481798878-31898-1-git-send-email-pmladek@suse.com [2] http://lkml.kernel.org/r/20161227141611.940-1-sergey.senozhatsky@gmail.com [3] http://lkml.kernel.org/r/20170215044332.30449-1-sergey.senozhatsky@gmail.com [4] http://lkml.kernel.org/r/20170217015932.11898-1-sergey.senozhatsky@gmail.com * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk: printk: drop call_console_drivers() unused param printk: convert the rest to printk-safe printk: remove zap_locks() function printk: use printk_safe buffers in printk printk: report lost messages in printk safe/nmi contexts printk: always use deferred printk when flush printk_safe lines printk: introduce per-cpu safe_print seq buffer printk: rename nmi.c and exported api printk: use vprintk_func in vprintk() MAINTAINERS: Add printk maintainers

printk: use rcuidle console tracepoint

2017-02-19T01:27:00Z

Use rcuidle console tracepoint because, apparently, it may be issued from an idle CPU: hw-breakpoint: Failed to enable monitor mode on CPU 0. hw-breakpoint: CPU 0 failed to disable vector catch =============================== [ ERR: suspicious RCU usage. ] 4.10.0-rc8-next-20170215+ #119 Not tainted ------------------------------- ./include/trace/events/printk.h:32 suspicious rcu_dereference_check() usage! other info that might help us debug this: RCU used illegally from idle CPU! rcu_scheduler_active = 2, debug_locks = 0 RCU used illegally from extended quiescent state! 2 locks held by swapper/0/0: #0: (cpu_pm_notifier_lock){......}, at: [] cpu_pm_exit+0x10/0x54 #1: (console_lock){+.+.+.}, at: [] vprintk_emit+0x264/0x474 stack backtrace: CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.10.0-rc8-next-20170215+ #119 Hardware name: Generic OMAP4 (Flattened Device Tree) console_unlock vprintk_emit vprintk_default printk reset_ctrl_regs dbg_cpu_pm_notify notifier_call_chain cpu_pm_exit omap_enter_idle_coupled cpuidle_enter_state cpuidle_enter_state_coupled do_idle cpu_startup_entry start_kernel This RCU warning, however, is suppressed by lockdep_off() in printk(). lockdep_off() increments the ->lockdep_recursion counter and thus disables RCU_LOCKDEP_WARN() and debug_lockdep_rcu_enabled(), which want lockdep to be enabled "current->lockdep_recursion == 0". Link: http://lkml.kernel.org/r/20170217015932.11898-1-sergey.senozhatsky@gmail.com Signed-off-by: Sergey Senozhatsky Reported-by: Tony Lindgren Tested-by: Tony Lindgren Acked-by: Paul E. McKenney Acked-by: Steven Rostedt (VMware) Cc: Petr Mladek Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Tony Lindgren Cc: Russell King Cc: [3.4+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

printk: drop call_console_drivers() unused param

2017-02-08T13:01:36Z

We do suppress_message_printing() check before we call call_console_drivers() now, so `level' param is not needed anymore. Link: http://lkml.kernel.org/r/20161224140902.1962-2-sergey.senozhatsky@gmail.com Cc: Andrew Morton Cc: Steven Rostedt Cc: Peter Hurley Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek

printk: convert the rest to printk-safe

2017-02-08T12:58:44Z

This patch converts the rest of logbuf users (which are out of printk recursion case, but can deadlock in printk). To make printk-safe usage easier the patch introduces 4 helper macros: - logbuf_lock_irq()/logbuf_unlock_irq() lock/unlock the logbuf lock and disable/enable local IRQ - logbuf_lock_irqsave(flags)/logbuf_unlock_irqrestore(flags) lock/unlock the logbuf lock and saves/restores local IRQ state Link: http://lkml.kernel.org/r/20161227141611.940-9-sergey.senozhatsky@gmail.com Cc: Andrew Morton Cc: Linus Torvalds Cc: Steven Rostedt Cc: Jan Kara Cc: Tejun Heo Cc: Calvin Owens Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Andy Lutomirski Cc: Peter Hurley Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek

printk: remove zap_locks() function

2017-02-08T12:54:27Z

We use printk-safe now which makes printk-recursion detection code in vprintk_emit() unreachable. The tricky thing here is that, apart from detecting and reporting printk recursions, that code also used to zap_locks() in case of panic() from the same CPU. However, zap_locks() does not look to be needed anymore: 1) Since commit 08d78658f393 ("panic: release stale console lock to always get the logbuf printed out") panic flushing of `logbuf' to console ignores the state of `console_sem' by doing panic() console_trylock(); console_unlock(); 2) Since commit cf9b1106c81c ("printk/nmi: flush NMI messages on the system panic") panic attempts to zap the `logbuf_lock' spin_lock to successfully flush nmi messages to `logbuf'. Basically, it seems that we either already do what zap_locks() used to do but in other places or we ignore the state of the lock. The only reaming difference is that we don't re-init the console semaphore in printk_safe_flush_on_panic(), but this is not necessary because we don't call console drivers from printk_safe_flush_on_panic() due to the fact that we are using a deferred printk() version (as was suggested by Petr Mladek). Link: http://lkml.kernel.org/r/20161227141611.940-8-sergey.senozhatsky@gmail.com Cc: Andrew Morton Cc: Linus Torvalds Cc: Steven Rostedt Cc: Jan Kara Cc: Tejun Heo Cc: Calvin Owens Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Andy Lutomirski Cc: Peter Hurley Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek

printk: use printk_safe buffers in printk

2017-02-08T12:51:49Z

Use printk_safe per-CPU buffers in printk recursion-prone blocks: -- around logbuf_lock protected sections in vprintk_emit() and console_unlock() -- around down_trylock_console_sem() and up_console_sem() Note that this solution addresses deadlocks caused by printk() recursive calls only. That is vprintk_emit() and console_unlock(). The rest will be converted in a followup patch. Another thing to note is that we now keep lockdep enabled in printk, because we are protected against the printk recursion caused by lockdep in vprintk_emit() by the printk-safe mechanism - we first switch to per-CPU buffers and only then access the deadlock-prone locks. Examples: 1) printk() from logbuf_lock spin_lock section Assume the following code: printk() raw_spin_lock(&logbuf_lock); WARN_ON(1); raw_spin_unlock(&logbuf_lock); which now produces: ------------[ cut here ]------------ WARNING: CPU: 0 PID: 366 at kernel/printk/printk.c:1811 vprintk_emit CPU: 0 PID: 366 Comm: bash Call Trace: warn_slowpath_null+0x1d/0x1f vprintk_emit+0x1cd/0x438 vprintk_default+0x1d/0x1f printk+0x48/0x50 [..] 2) printk() from semaphore sem->lock spin_lock section Assume the following code printk() console_trylock() down_trylock() raw_spin_lock_irqsave(&sem->lock, flags); WARN_ON(1); raw_spin_unlock_irqrestore(&sem->lock, flags); which now produces: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 363 at kernel/locking/semaphore.c:141 down_trylock CPU: 1 PID: 363 Comm: bash Call Trace: warn_slowpath_null+0x1d/0x1f down_trylock+0x3d/0x62 ? vprintk_emit+0x3f9/0x414 console_trylock+0x31/0xeb vprintk_emit+0x3f9/0x414 vprintk_default+0x1d/0x1f printk+0x48/0x50 [..] 3) printk() from console_unlock() Assume the following code: printk() console_unlock() raw_spin_lock(&logbuf_lock); WARN_ON(1); raw_spin_unlock(&logbuf_lock); which now produces: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 329 at kernel/printk/printk.c:2384 console_unlock CPU: 1 PID: 329 Comm: bash Call Trace: warn_slowpath_null+0x18/0x1a console_unlock+0x12d/0x559 ? trace_hardirqs_on_caller+0x16d/0x189 ? trace_hardirqs_on+0xd/0xf vprintk_emit+0x363/0x374 vprintk_default+0x18/0x1a printk+0x43/0x4b [..] 4) printk() from try_to_wake_up() Assume the following code: printk() console_unlock() up() try_to_wake_up() raw_spin_lock_irqsave(&p->pi_lock, flags); WARN_ON(1); raw_spin_unlock_irqrestore(&p->pi_lock, flags); which now produces: ------------[ cut here ]------------ WARNING: CPU: 3 PID: 363 at kernel/sched/core.c:2028 try_to_wake_up CPU: 3 PID: 363 Comm: bash Call Trace: warn_slowpath_null+0x1d/0x1f try_to_wake_up+0x7f/0x4f7 wake_up_process+0x15/0x17 __up.isra.0+0x56/0x63 up+0x32/0x42 __up_console_sem+0x37/0x55 console_unlock+0x21e/0x4c2 vprintk_emit+0x41c/0x462 vprintk_default+0x1d/0x1f printk+0x48/0x50 [..] 5) printk() from call_console_drivers() Assume the following code: printk() console_unlock() call_console_drivers() ... WARN_ON(1); which now produces: ------------[ cut here ]------------ WARNING: CPU: 2 PID: 305 at kernel/printk/printk.c:1604 call_console_drivers CPU: 2 PID: 305 Comm: bash Call Trace: warn_slowpath_null+0x18/0x1a call_console_drivers.isra.6.constprop.16+0x3a/0xb0 console_unlock+0x471/0x48e vprintk_emit+0x1f4/0x206 vprintk_default+0x18/0x1a vprintk_func+0x6e/0x70 printk+0x3e/0x46 [..] 6) unsupported placeholder in printk() format now prints an actual warning from vscnprintf(), instead of 'BUG: recent printk recursion!'. ------------[ cut here ]------------ WARNING: CPU: 5 PID: 337 at lib/vsprintf.c:1900 format_decode Please remove unsupported % in format string CPU: 5 PID: 337 Comm: bash Call Trace: dump_stack+0x4f/0x65 __warn+0xc2/0xdd warn_slowpath_fmt+0x4b/0x53 format_decode+0x22c/0x308 vsnprintf+0x89/0x3b7 vscnprintf+0xd/0x26 vprintk_emit+0xb4/0x238 vprintk_default+0x1d/0x1f vprintk_func+0x6c/0x73 printk+0x43/0x4b [..] Link: http://lkml.kernel.org/r/20161227141611.940-7-sergey.senozhatsky@gmail.com Cc: Andrew Morton Cc: Linus Torvalds Cc: Jan Kara Cc: Tejun Heo Cc: Calvin Owens Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Andy Lutomirski Cc: Peter Hurley Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek Reviewed-by: Steven Rostedt (VMware)

printk: report lost messages in printk safe/nmi contexts

2017-02-08T12:50:05Z

Account lost messages in pritk-safe and printk-safe-nmi contexts and report those numbers during printk_safe_flush(). The patch also moves lost message counter to struct `printk_safe_seq_buf' instead of having dedicated static counters - this simplifies the code. Link: http://lkml.kernel.org/r/20161227141611.940-6-sergey.senozhatsky@gmail.com Cc: Andrew Morton Cc: Linus Torvalds Cc: Steven Rostedt Cc: Jan Kara Cc: Tejun Heo Cc: Calvin Owens Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Andy Lutomirski Cc: Peter Hurley Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek