user/sven/linux.git/include/linux/percpu.h, branch v4.9.147

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

percpu: remove PERCPU_ENOUGH_ROOM which is stale definition

2015-11-16T15:50:25Z

As pure cleanup, this patch removes PERCPU_ENOUGH_ROOM which is not used any more. That is, no code refers to the definition. Acked-by: Christoph Lameter Signed-off-by: Jungseok Lee Signed-off-by: Tejun Heo

printk/percpu: Define printk_func when printk is not defined

2014-11-21T16:19:15Z

To avoid include hell, the per_cpu variable printk_func was declared in percpu.h. But it is only defined if printk is defined. As users of printk may also use the printk_func variable, it needs to be defined even if CONFIG_PRINTK is not. Also add a printk.h include in percpu.h just to be safe. Link: http://lkml.kernel.org/r/20141121183215.01ba539c@canb.auug.org.au Reported-by: Stephen Rothwell Signed-off-by: Steven Rostedt

printk: Add per_cpu printk func to allow printk to be diverted

2014-11-20T03:01:21Z

Being able to divert printk to call another function besides the normal logging is useful for such things like NMI handling. If some functions are to be called from NMI that does printk() it is possible to lock up the box if the nmi handler triggers when another printk is happening. One example of this use is to perform a stack trace on all CPUs via NMI. But if the NMI is to do the printk() it can cause the system to lock up. By allowing the printk to be diverted to another function that can safely record the printk output and then print it when it in a safe context then NMIs will be safe to call these functions like show_regs(). Link: http://lkml.kernel.org/p/20140619213952.209176403@goodmis.org Tested-by: Jiri Kosina Acked-by: Jiri Kosina Acked-by: Paul E. McKenney Reviewed-by: Petr Mladek Signed-off-by: Steven Rostedt

percpu: implement asynchronous chunk population

2014-09-02T18:46:05Z

The percpu allocator now supports atomic allocations by only allocating from already populated areas but the mechanism to ensure that there's adequate amount of populated areas was missing. This patch expands pcpu_balance_work so that in addition to freeing excess free chunks it also populates chunks to maintain an adequate level of populated areas. pcpu_alloc() schedules pcpu_balance_work if the amount of free populated areas is too low or after an atomic allocation failure. * PERPCU_DYNAMIC_RESERVE is increased by two pages to account for PCPU_EMPTY_POP_PAGES_LOW. * pcpu_async_enabled is added to gate both async jobs - chunk->map_extend_work and pcpu_balance_work - so that we don't end up scheduling them while the needed subsystems aren't up yet. Signed-off-by: Tejun Heo

percpu: implement [__]alloc_percpu_gfp()

2014-09-02T18:46:04Z

Now that pcpu_alloc_area() can allocate only from populated areas, it's easy to add atomic allocation support to [__]alloc_percpu(). Update pcpu_alloc() so that it accepts @gfp and skips all the blocking operations and allocates only from the populated areas if @gfp doesn't contain GFP_KERNEL. New interface functions [__]alloc_percpu_gfp() are added. While this means that atomic allocations are possible, this isn't complete yet as there's no mechanism to ensure that certain amount of populated areas is kept available and atomic allocations may keep failing under certain conditions. Signed-off-by: Tejun Heo

percpu: move {raw|this}_cpu_*() definitions to include/linux/percpu-defs.h

2014-06-17T23:12:39Z

We're in the process of moving all percpu accessors and operations to include/linux/percpu-defs.h so that they're available to arch headers without having to include full include/linux/percpu.h which may cause cyclic inclusion dependency. This patch moves {raw|this}_cpu_*() definitions from include/linux/percpu.h to include/linux/percpu-defs.h. The code is moved mostly verbatim; however, raw_cpu_*() are placed above this_cpu_*() which is more conventional as the raw operations may be used to defined other variants. This is pure reorganization. Signed-off-by: Tejun Heo Acked-by: Christoph Lameter

percpu: move generic {raw|this}_cpu_*_N() definitions to include/asm-generic/percpu.h

2014-06-17T23:12:39Z

{raw|this}_cpu_*_N() operations are expected to be provided by archs and the generic definitions are provided as fallbacks. As such, these firmly belong to include/asm-generic/percpu.h. Move the generic definitions to include/asm-generic/percpu.h. The code is moved mostly verbatim; however, raw_cpu_*_N() are placed above this_cpu_*_N() which is more conventional as the raw operations may be used to defined other variants. This is pure reorganization. Signed-off-by: Tejun Heo Acked-by: Christoph Lameter

percpu: only allow sized arch overrides for {raw|this}_cpu_*() ops

2014-06-17T23:12:39Z

Currently, percpu allows two separate methods for overriding {raw|this}_cpu_*() ops - for a given operation, an arch can provide whole replacement or sized sub operations to override specific parts of it. e.g. arch either can provide this_cpu_add() or this_cpu_add_4() to override only the 4 byte operation. While quite flexible on a glance, the dual-overriding scheme complicates the code path for no actual gain. It compilcates the already complex operation definitions and if an arch wants to override all sizes, it can easily provide all variants anyway. In fact, no arch is actually making use of whole operation override. Another oddity is that __this_cpu_*() operations are defined in the same way as raw_cpu_*() but ignores full overrides of the raw_cpu_*() and doesn't allow full operation override, so if an arch provides whole overrides for raw_cpu_*() operations __this_cpu_*() ends up using the generic implementations. More importantly, it takes away the layering between arch-specific and generic parts making it impossible for the generic part to implement arch-independent features on top of arch-specific overrides. This patch removes the support for whole operation overrides. As no arch is using it, this doesn't cause any actual difference. Signed-off-by: Tejun Heo Acked-by: Christoph Lameter

percpu: move accessors from include/linux/percpu.h to percpu-defs.h

2014-06-17T23:12:34Z

include/linux/percpu-defs.h is gonna host all accessors and operations so that arch headers can make use of them too without worrying about circular dependency through include/linux/percpu.h. This patch moves the following accessors from include/linux/percpu.h to include/linux/percpu-defs.h. * get/put_cpu_var() * get/put_cpu_ptr() * per_cpu_ptr() This is pure reorgniazation. Signed-off-by: Tejun Heo Acked-by: Christoph Lameter