pm24.git/kernel/cpu.c, branch v3.7-rc3

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

smp, idle: Allocate idle thread for each possible cpu during boot

2012-05-03T17:32:34Z

percpu areas are already allocated during boot for each possible cpu. percpu idle threads can be considered as an extension of the percpu areas, and allocate them for each possible cpu during boot. This will eliminate the need for workqueue based idle thread allocation. In future we can move the idle thread area into the percpu area too. [ tglx: Moved the loop into smpboot.c and added an error check when the init code failed to allocate an idle thread for a cpu which should be onlined ] Signed-off-by: Suresh Siddha Cc: Peter Zijlstra Cc: Rusty Russell Cc: Paul E. McKenney Cc: Srivatsa S. Bhat Cc: Tejun Heo Cc: David Rientjes Cc: venki@google.com Link: http://lkml.kernel.org/r/1334966930.28674.245.camel@sbsiddha-desk.sc.intel.com Signed-off-by: Thomas Gleixner

smp: Provide generic idle thread allocation

2012-04-26T10:06:09Z

All SMP architectures have magic to fork the idle task and to store it for reusage when cpu hotplug is enabled. Provide a generic infrastructure for it. Create/reinit the idle thread for the cpu which is brought up in the generic code and hand the thread pointer to the architecture code via __cpu_up(). Note, that fork_idle() is called via a workqueue, because this guarantees that the idle thread does not get a reference to a user space VM. This can happen when the boot process did not bring up all possible cpus and a later cpu_up() is initiated via the sysfs interface. In that case fork_idle() would be called in the context of the user space task and take a reference on the user space VM. Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Rusty Russell Cc: Paul E. McKenney Cc: Srivatsa S. Bhat Cc: Matt Turner Cc: Russell King Cc: Mike Frysinger Cc: Jesper Nilsson Cc: Richard Kuo Cc: Tony Luck Cc: Hirokazu Takata Cc: Ralf Baechle Cc: David Howells Cc: James E.J. Bottomley Cc: Benjamin Herrenschmidt Cc: Martin Schwidefsky Cc: Paul Mundt Cc: David S. Miller Cc: Chris Metcalf Cc: Richard Weinberger Cc: x86@kernel.org Acked-by: Venkatesh Pallipadi Link: http://lkml.kernel.org/r/20120420124557.102478630@linutronix.de

smp: Add generic smpboot facility

2012-04-26T10:06:09Z

Start a new file, which will hold SMP and CPU hotplug related generic infrastructure. Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Rusty Russell Cc: Paul E. McKenney Cc: Srivatsa S. Bhat Cc: Matt Turner Cc: Russell King Cc: Mike Frysinger Cc: Jesper Nilsson Cc: Richard Kuo Cc: Tony Luck Cc: Hirokazu Takata Cc: Ralf Baechle Cc: David Howells Cc: James E.J. Bottomley Cc: Benjamin Herrenschmidt Cc: Martin Schwidefsky Cc: Paul Mundt Cc: David S. Miller Cc: Chris Metcalf Cc: Richard Weinberger Cc: x86@kernel.org Link: http://lkml.kernel.org/r/20120420124557.035417523@linutronix.de