user/sven/linux.git/kernel/cpu.c, branch v3.8.10

Merge branch 'x86-bsp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2012-12-12T03:56:33Z

Pull x86 BSP hotplug changes from Ingo Molnar: "This tree enables CPU#0 (the boot processor) to be onlined/offlined on x86, just like any other CPU. Enabled on Intel CPUs for now. Allowing this required the identification and fixing of latent CPU#0 assumptions (such as CPU#0 initializations, etc.) in the x86 architecture code, plus the identification of barriers to BSP-offlining, such as active PIC interrupts which can only be serviced on the BSP. It's behind a default-off option, and there's a debug option that allows the automatic testing of this feature. The motivation of this feature is to allow and prepare for true CPU-hotplug hardware support: recent changes to MCE support enable us to detect a deteriorating but not yet hard-failing L1/L2 cache on a CPU that could be soft-unplugged - or a failing L3 cache on a multi-socket system. Note that true hardware hot-plug is not yet fully enabled by this, because that requires a special platform wakeup sequence to be sent to the freshly powered up CPU#0. Future patches for this are planned, once such a platform exists. Chicken and egg" * 'x86-bsp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86, topology: Debug CPU0 hotplug x86/i387.c: Initialize thread xstate only on CPU0 only once x86, hotplug: Handle retrigger irq by the first available CPU x86, hotplug: The first online processor saves the MTRR state x86, hotplug: During CPU0 online, enable x2apic, set_numa_node. x86, hotplug: Wake up CPU0 via NMI instead of INIT, SIPI, SIPI x86-32, hotplug: Add start_cpu0() entry point to head_32.S x86-64, hotplug: Add start_cpu0() entry point to head_64.S kernel/cpu.c: Add comment for priority in cpu_hotplug_pm_callback x86, hotplug, suspend: Online CPU0 for suspend or hibernate x86, hotplug: Support functions for CPU0 online/offline x86, topology: Don't offline CPU0 if any PIC irq can not be migrated out of it x86, Kconfig: Add config switch for CPU0 hotplug doc: Add x86 CPU0 online/offline feature

ACPI / processor: prevent cpu from becoming online

2012-11-14T23:16:00Z

Even if acpi_processor_handle_eject() offlines cpu, there is a chance to online the cpu after that. So the patch closes the window by using get/put_online_cpus(). Why does the patch change _cpu_up() logic? The patch cares the race of hot-remove cpu and _cpu_up(). If the patch does not change it, there is the following race. hot-remove cpu | _cpu_up() ------------------------------------- ------------------------------------ call acpi_processor_handle_eject() | call cpu_down() | call get_online_cpus() | | call cpu_hotplug_begin() and stop here call arch_unregister_cpu() | call acpi_unmap_lsapic() | call put_online_cpus() | | start and continue _cpu_up() return acpi_processor_remove() | continue hot-remove the cpu | So _cpu_up() can continue to itself. And hot-remove cpu can also continue itself. If the patch changes _cpu_up() logic, the race disappears as below: hot-remove cpu | _cpu_up() ----------------------------------------------------------------------- call acpi_processor_handle_eject() | call cpu_down() | call get_online_cpus() | | call cpu_hotplug_begin() and stop here call arch_unregister_cpu() | call acpi_unmap_lsapic() | cpu's cpu_present is set | to false by set_cpu_present()| call put_online_cpus() | | start _cpu_up() | check cpu_present() and return -EINVAL return acpi_processor_remove() | continue hot-remove the cpu | Signed-off-by: Yasuaki Ishimatsu Reviewed-by: Srivatsa S. Bhat Reviewed-by: Toshi Kani Signed-off-by: Rafael J. Wysocki

kernel/cpu.c: Add comment for priority in cpu_hotplug_pm_callback

2012-11-14T17:39:50Z

cpu_hotplug_pm_callback should have higher priority than bsp_pm_callback which depends on cpu_hotplug_pm_callback to disable cpu hotplug to avoid race during bsp online checking. This is to hightlight the priorities between the two callbacks in case people may overlook the order. Ideally the priorities should be defined in macro/enum instead of fixed values. To do that, a seperate patchset may be pushed which will touch serveral other generic files and is out of scope of this patchset. Signed-off-by: Fenghua Yu Link: http://lkml.kernel.org/r/1352835171-3958-7-git-send-email-fenghua.yu@intel.com Reviewed-by: Srivatsa S. Bhat Acked-by: Rafael J. Wysocki Signed-off-by: H. Peter Anvin

CPU hotplug, debug: detect imbalance between get_online_cpus() and put_online_cpus()

2012-10-09T07:22:15Z

The synchronization between CPU hotplug readers and writers is achieved by means of refcounting, safeguarded by the cpu_hotplug.lock. get_online_cpus() increments the refcount, whereas put_online_cpus() decrements it. If we ever hit an imbalance between the two, we end up compromising the guarantees of the hotplug synchronization i.e, for example, an extra call to put_online_cpus() can end up allowing a hotplug reader to execute concurrently with a hotplug writer. So, add a WARN_ON() in put_online_cpus() to detect such cases where the refcount can go negative, and also attempt to fix it up, so that we can continue to run. Signed-off-by: Srivatsa S. Bhat Reviewed-by: Yasuaki Ishimatsu Cc: Jiri Kosina Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2012-10-01T17:46:27Z

Pull x86/asm changes from Ingo Molnar: "The one change that stands out is the alternatives patching change that prevents us from ever patching back instructions from SMP to UP: this simplifies things and speeds up CPU hotplug. Other than that it's smaller fixes, cleanups and improvements." * 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86: Unspaghettize do_trap() x86_64: Work around old GAS bug x86: Use REP BSF unconditionally x86: Prefer TZCNT over BFS x86/64: Adjust types of temporaries used by ffs()/fls()/fls64() x86: Drop unnecessary kernel_eflags variable on 64-bit x86/smp: Don't ever patch back to UP if we unplug cpus

x86/smp: Don't ever patch back to UP if we unplug cpus

2012-08-23T08:45:13Z

We still patch SMP instructions to UP variants if we boot with a single CPU, but not at any other time. In particular, not if we unplug CPUs to return to a single cpu. Paul McKenney points out: mean offline overhead is 6251/48=130.2 milliseconds. If I remove the alternatives_smp_switch() from the offline path [...] the mean offline overhead is 550/42=13.1 milliseconds Basically, we're never going to get those 120ms back, and the code is pretty messy. We get rid of: 1) The "smp-alt-once" boot option. It's actually "smp-alt-boot", the documentation is wrong. It's now the default. 2) The skip_smp_alternatives flag used by suspend. 3) arch_disable_nonboot_cpus_begin() and arch_disable_nonboot_cpus_end() which were only used to set this one flag. Signed-off-by: Rusty Russell Cc: Paul McKenney Cc: Suresh Siddha Cc: Linus Torvalds Cc: Andrew Morton Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/87vcgwwive.fsf@rustcorp.com.au Signed-off-by: Ingo Molnar

smpboot: Provide infrastructure for percpu hotplug threads

2012-08-13T15:01:07Z

Provide a generic interface for setting up and tearing down percpu threads. On registration the threads for already online cpus are created and started. On deregistration (modules) the threads are stoppped. During hotplug operations the threads are created, started, parked and unparked. The datastructure for registration provides a pointer to percpu storage space and optional setup, cleanup, park, unpark functions. These functions are called when the thread state changes. Each implementation has to provide a function which is queried and returns whether the thread should run and the thread function itself. The core code handles all state transitions and avoids duplicated code in the call sites. [ paulmck: Preemption leak fix ] Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Reviewed-by: Srivatsa S. Bhat Cc: Rusty Russell Reviewed-by: Paul E. McKenney Cc: Namhyung Kim Link: http://lkml.kernel.org/r/20120716103948.352501068@linutronix.de Signed-off-by: Thomas Gleixner

mm/hotplug: correctly setup fallback zonelists when creating new pgdat

2012-08-01T01:42:44Z

When hotadd_new_pgdat() is called to create new pgdat for a new node, a fallback zonelist should be created for the new node. There's code to try to achieve that in hotadd_new_pgdat() as below: /* * The node we allocated has no zone fallback lists. For avoiding * to access not-initialized zonelist, build here. */ mutex_lock(&zonelists_mutex); build_all_zonelists(pgdat, NULL); mutex_unlock(&zonelists_mutex); But it doesn't work as expected. When hotadd_new_pgdat() is called, the new node is still in offline state because node_set_online(nid) hasn't been called yet. And build_all_zonelists() only builds zonelists for online nodes as: for_each_online_node(nid) { pg_data_t *pgdat = NODE_DATA(nid); build_zonelists(pgdat); build_zonelist_cache(pgdat); } Though we hope to create zonelist for the new pgdat, but it doesn't. So add a new parameter "pgdat" the build_all_zonelists() to build pgdat for the new pgdat too. Signed-off-by: Jiang Liu Signed-off-by: Xishi Qiu Cc: Mel Gorman Cc: Michal Hocko Cc: Minchan Kim Cc: Rusty Russell Cc: Yinghai Lu Cc: Tony Luck Cc: KAMEZAWA Hiroyuki Cc: KOSAKI Motohiro Cc: David Rientjes Cc: Keping Chen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

kernel/cpu.c: document clear_tasks_mm_cpumask()

2012-06-01T00:49:30Z

Add more comments on clear_tasks_mm_cpumask, plus adds a runtime check: the function is only suitable for offlined CPUs, and if called inappropriately, the kernel should scream aloud. [akpm@linux-foundation.org: tweak comment: s/walks up/walks/, use 80 cols] Suggested-by: Andrew Morton Suggested-by: Peter Zijlstra Signed-off-by: Anton Vorontsov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

cpu: introduce clear_tasks_mm_cpumask() helper

2012-06-01T00:49:29Z

Many architectures clear tasks' mm_cpumask like this: read_lock(&tasklist_lock); for_each_process(p) { if (p->mm) cpumask_clear_cpu(cpu, mm_cpumask(p->mm)); } read_unlock(&tasklist_lock); Depending on the context, the code above may have several problems, such as: 1. Working with task->mm w/o getting mm or grabing the task lock is dangerous as ->mm might disappear (exit_mm() assigns NULL under task_lock(), so tasklist lock is not enough). 2. Checking for process->mm is not enough because process' main thread may exit or detach its mm via use_mm(), but other threads may still have a valid mm. This patch implements a small helper function that does things correctly, i.e.: 1. We take the task's lock while whe handle its mm (we can't use get_task_mm()/mmput() pair as mmput() might sleep); 2. To catch exited main thread case, we use find_lock_task_mm(), which walks up all threads and returns an appropriate task (with task lock held). Also, Per Peter Zijlstra's idea, now we don't grab tasklist_lock in the new helper, instead we take the rcu read lock. We can do this because the function is called after the cpu is taken down and marked offline, so no new tasks will get this cpu set in their mm mask. Signed-off-by: Anton Vorontsov Cc: Richard Weinberger Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Russell King Cc: Benjamin Herrenschmidt Cc: Mike Frysinger Cc: Paul Mundt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds