The patch titled Subject: kernel/cpu.c: document clear_tasks_mm_cpumask() has been removed from the -mm tree. Its filename was kernel-cpuc-document-clear_tasks_mm_cpumask.patch This patch was dropped because it was merged into mainline or a subsystem tree The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ From: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx> Subject: kernel/cpu.c: document clear_tasks_mm_cpumask() 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@xxxxxxxxxxxxxxxxxxxx: tweak comment: s/walks up/walks/, use 80 cols] Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Suggested-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Signed-off-by: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/cpu.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff -puN kernel/cpu.c~kernel-cpuc-document-clear_tasks_mm_cpumask kernel/cpu.c --- a/kernel/cpu.c~kernel-cpuc-document-clear_tasks_mm_cpumask +++ a/kernel/cpu.c @@ -13,6 +13,7 @@ #include <linux/oom.h> #include <linux/rcupdate.h> #include <linux/export.h> +#include <linux/bug.h> #include <linux/kthread.h> #include <linux/stop_machine.h> #include <linux/mutex.h> @@ -175,6 +176,18 @@ void __ref unregister_cpu_notifier(struc } EXPORT_SYMBOL(unregister_cpu_notifier); +/** + * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU + * @cpu: a CPU id + * + * This function walks all processes, finds a valid mm struct for each one and + * then clears a corresponding bit in mm's cpumask. While this all sounds + * trivial, there are various non-obvious corner cases, which this function + * tries to solve in a safe manner. + * + * Also note that the function uses a somewhat relaxed locking scheme, so it may + * be called only for an already offlined CPU. + */ void clear_tasks_mm_cpumask(int cpu) { struct task_struct *p; @@ -186,10 +199,15 @@ void clear_tasks_mm_cpumask(int cpu) * Thus, we may use rcu_read_lock() here, instead of grabbing * full-fledged tasklist_lock. */ + WARN_ON(cpu_online(cpu)); rcu_read_lock(); for_each_process(p) { struct task_struct *t; + /* + * Main thread might exit, but other threads may still have + * a valid mm. Find one. + */ t = find_lock_task_mm(p); if (!t) continue; _ Patches currently in -mm which might be from anton.vorontsov@xxxxxxxxxx are origin.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html