user/sven/linux.git/include/linux/hardirq.h, branch v4.9.191

printk/nmi: generic solution for safe printk in NMI

2016-05-21T00:58:30Z

printk() takes some locks and could not be used a safe way in NMI context. The chance of a deadlock is real especially when printing stacks from all CPUs. This particular problem has been addressed on x86 by the commit a9edc8809328 ("x86/nmi: Perform a safe NMI stack trace on all CPUs"). The patchset brings two big advantages. First, it makes the NMI backtraces safe on all architectures for free. Second, it makes all NMI messages almost safe on all architectures (the temporary buffer is limited. We still should keep the number of messages in NMI context at minimum). Note that there already are several messages printed in NMI context: WARN_ON(in_nmi()), BUG_ON(in_nmi()), anything being printed out from MCE handlers. These are not easy to avoid. This patch reuses most of the code and makes it generic. It is useful for all messages and architectures that support NMI. The alternative printk_func is set when entering and is reseted when leaving NMI context. It queues IRQ work to copy the messages into the main ring buffer in a safe context. __printk_nmi_flush() copies all available messages and reset the buffer. Then we could use a simple cmpxchg operations to get synchronized with writers. There is also used a spinlock to get synchronized with other flushers. We do not longer use seq_buf because it depends on external lock. It would be hard to make all supported operations safe for a lockless use. It would be confusing and error prone to make only some operations safe. The code is put into separate printk/nmi.c as suggested by Steven Rostedt. It needs a per-CPU buffer and is compiled only on architectures that call nmi_enter(). This is achieved by the new HAVE_NMI Kconfig flag. The are MN10300 and Xtensa architectures. We need to clean up NMI handling there first. Let's do it separately. The patch is heavily based on the draft from Peter Zijlstra, see https://lkml.org/lkml/2015/6/10/327 [arnd@arndb.de: printk-nmi: use %zu format string for size_t] [akpm@linux-foundation.org: min_t->min - all types are size_t here] Signed-off-by: Petr Mladek Suggested-by: Peter Zijlstra Suggested-by: Steven Rostedt Cc: Jan Kara Acked-by: Russell King [arm part] Cc: Daniel Thompson Cc: Jiri Kosina Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Ralf Baechle Cc: Benjamin Herrenschmidt Cc: Martin Schwidefsky Cc: David Miller Cc: Daniel Thompson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

sched/preempt: Merge preempt_mask.h into preempt.h

2015-05-19T06:39:11Z

preempt_mask.h defines all the preempt_count semantics and related symbols: preempt, softirq, hardirq, nmi, preempt active, need resched, etc... preempt.h defines the accessors and mutators of preempt_count. But there is a messy dependency game around those two header files: * preempt_mask.h includes preempt.h in order to access preempt_count() * preempt_mask.h defines all preempt_count semantic and symbols except PREEMPT_NEED_RESCHED that is needed by asm/preempt.h Thus we need to define it from preempt.h, right before including asm/preempt.h, instead of defining it to preempt_mask.h with the other preempt_count symbols. Therefore the preempt_count semantics happen to be spread out. * We plan to introduce preempt_active_[enter,exit]() to consolidate preempt_schedule*() code. But we'll need to access both preempt_count mutators (preempt_count_add()) and preempt_count symbols (PREEMPT_ACTIVE, PREEMPT_OFFSET). The usual place to define preempt operations is in preempt.h but then we'll need symbols in preempt_mask.h which already includes preempt.h. So we end up with a ressource circle dependency. Lets merge preempt_mask.h into preempt.h to solve these dependency issues. This way we gather semantic symbols and operation definition of preempt_count in a single file. This is a dumb copy-paste merge. Further merge re-arrangments are performed in a subsequent patch to ease review. Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1431441711-29753-2-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar

genirq: Provide disable_hardirq()

2015-02-18T14:08:33Z

For things like netpoll there is a need to disable an interrupt from atomic context. Currently netpoll uses disable_irq() which will sleep-wait on threaded handlers and thus forced_irqthreads breaks things. Provide disable_hardirq(), which uses synchronize_hardirq() to only wait for active hardirq handlers; also change synchronize_hardirq() to return the status of threaded handlers. This will allow one to try-disable an interrupt from atomic context, or in case of request_threaded_irq() to only wait for the hardirq part. Suggested-by: Sabrina Dubroca Signed-off-by: Peter Zijlstra (Intel) Cc: Arnd Bergmann Cc: David Miller Cc: Eyal Perry Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Quentin Lambert Cc: Randy Dunlap Cc: Russell King Link: http://lkml.kernel.org/r/20150205130623.GH5029@twins.programming.kicks-ass.net [ Fixed typos and such. ] Signed-off-by: Ingo Molnar

genirq: Provide synchronize_hardirq()

2014-02-19T16:22:44Z

synchronize_irq() waits for hard irq and threaded handlers to complete before returning. For some special cases we only need to make sure that the hard interrupt part of the irq line is not in progress when we disabled the - possibly shared - interrupt at the device level. A proper use case for this was provided by Russell. The sdhci driver requires some irq triggered functions to be run in thread context. The current implementation of the thread context is a sdio private kthread construct, which has quite some shortcomings. These can be avoided when the thread is directly associated to the device interrupt via the generic threaded irq infrastructure. Though there is a corner case related to run time power management where one side disables the device interrupts at the device level and needs to make sure, that an already running hard interrupt handler has completed before proceeding further. Though that hard interrupt handler might wake the associated thread, which in turn can request the runtime PM to reenable the device. Using synchronize_irq() leads to an immediate deadlock of the irq thread waiting for the PM lock and the synchronize_irq() waiting for the irq thread to complete. Due to the fact that it is sufficient for this case to ensure that no hard irq handler is executing a new function which avoids the check for the thread is required. Add a function, which just monitors the hard irq parts and ignores the threaded handlers. Signed-off-by: Thomas Gleixner Tested-by: Russell King Cc: Chris Ball Acked-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20140215003823.653236081@linutronix.de

sched/preempt, locking: Rework local_bh_{dis,en}able()

2014-01-13T16:32:27Z

Currently local_bh_disable() is out-of-line for no apparent reason. So inline it to save a few cycles on call/return nonsense, the function body is a single add on x86 (a few loads and store extra on load/store archs). Also expose two new local_bh functions: __local_bh_{dis,en}able_ip(unsigned long ip, unsigned int cnt); Which implement the actual local_bh_{dis,en}able() behaviour. The next patch uses the exposed @cnt argument to optimize bh lock functions. With build fixes from Jacob Pan. Cc: rjw@rjwysocki.net Cc: rui.zhang@intel.com Cc: jacob.jun.pan@linux.intel.com Cc: Mike Galbraith Cc: hpa@zytor.com Cc: Arjan van de Ven Cc: lenb@kernel.org Reviewed-by: Thomas Gleixner Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20131119151338.GF3694@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar

sched: Extract the basic add/sub preempt_count modifiers

2013-09-25T12:07:54Z

Rewrite the preempt_count macros in order to extract the 3 basic preempt_count value modifiers: __preempt_count_add() __preempt_count_sub() and the new: __preempt_count_dec_and_test() And since we're at it anyway, replace the unconventional $op_preempt_count names with the more conventional preempt_count_$op. Since these basic operators are equivalent to the previous _notrace() variants, do away with the _notrace() versions. Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/n/tip-ewbpdbupy9xpsjhg960zwbv8@git.kernel.org Signed-off-by: Ingo Molnar

Remove GENERIC_HARDIRQ config option

2013-09-13T13:09:52Z

After the last architecture switched to generic hard irqs the config options HAVE_GENERIC_HARDIRQS & GENERIC_HARDIRQS and the related code for !CONFIG_GENERIC_HARDIRQS can be removed. Signed-off-by: Martin Schwidefsky

hardirq: Split preempt count mask definitions

2013-08-14T15:14:52Z

In order to use static keys with vtime APIs, we'll need to add static keys headers to vtime.h hardirq.h then becomes a problem because it needs vtime.h for irqtime accounting in irq_enter/irq_exit, but it's often included just to get the irq mask definitions in the task preempt_count field and the APIs that come along: in_interrupt(), in_hardirq(), etc... Some very low level arch headers sometimes need these masks and APIs such as arch/m68k/include/asm/irqflags.h for example. But they don't want to include hardirq.h if vtime.h, jump_label.h and even workqueue.h come along. Including such bloated high level header from arch headers can quickly result in circular headers dependency that crash the build. So let's split hardirq.h in two parts: * preempt_mask.h that gathers all the preempt_count definitions and the APIs associated. This one is considered low level and can be safely included anywhere. * hardirq.h that includes the previous one. It defines the irq entry/exit APIs. To avoid future circular headers dependencies, the preempt_mask.h inclusion can replace hardirq.h on files that don't implement irq low level handlers but just need the atomic/context check APIs. Signed-off-by: Frederic Weisbecker Cc: Steven Rostedt Cc: Paul E. McKenney Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Borislav Petkov Cc: Li Zhong Cc: Mike Galbraith Cc: Kevin Hilman

rcu: Remove TINY_PREEMPT_RCU

2013-06-10T20:45:49Z

TINY_PREEMPT_RCU adds significant code and complexity, but does not offer commensurate benefits. People currently using TINY_PREEMPT_RCU can get much better memory footprint with TINY_RCU, or, if they really need preemptible RCU, they can use TREE_PREEMPT_RCU with a relatively minor degradation in memory footprint. Please note that this move has been widely publicized on LKML (https://lkml.org/lkml/2012/11/12/545) and on LWN (http://lwn.net/Articles/541037/). This commit therefore removes TINY_PREEMPT_RCU. Signed-off-by: Paul E. McKenney [ paulmck: Updated to eliminate #else in rcutiny.h as suggested by Josh ] Reviewed-by: Josh Triplett

irq: Remove IRQ_EXIT_OFFSET workaround

2013-02-21T23:05:07Z

The IRQ_EXIT_OFFSET trick was used to make sure the irq doesn't get preempted after we substract the HARDIRQ_OFFSET until we are entirely done with any code in irq_exit(). This workaround was necessary because some archs may call irq_exit() with irqs enabled and there is still some code in the end of this function that is not covered by the HARDIRQ_OFFSET but want to stay non-preemptible. Now that irq are always disabled in irq_exit(), the whole code is guaranteed not to be preempted. We can thus remove this hack. Signed-off-by: Frederic Weisbecker Cc: Linus Torvalds Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Paul E. McKenney