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/*

 *  linux/mm/oom_kill.c

 *

 *  Copyright (C)  1998,2000  Rik van Riel

 *      Thanks go out to Claus Fischer for some serious inspiration and

 *      for goading me into coding this file...

 *

 *  The routines in this file are used to kill a process when

 *  we're seriously out of memory. This gets called from __alloc_pages()

 *  in mm/page_alloc.c when we really run out of memory.

 *

 *  Since we won't call these routines often (on a well-configured

 *  machine) this file will double as a 'coding guide' and a signpost

 *  for newbie kernel hackers. It features several pointers to major

 *  kernel subsystems and hints as to where to find out what things do.

 */

#include <linux/oom.h>

#include <linux/mm.h>

#include <linux/err.h>

#include <linux/sched.h>

#include <linux/swap.h>

#include <linux/timex.h>

#include <linux/jiffies.h>

#include <linux/cpuset.h>

#include <linux/module.h>

#include <linux/notifier.h>

int sysctl_panic_on_oom;

int sysctl_oom_kill_allocating_task;

static DEFINE_SPINLOCK(zone_scan_mutex);

/* #define DEBUG */

/**

 * badness - calculate a numeric value for how bad this task has been

 * @p: task struct of which task we should calculate

 * @uptime: current uptime in seconds

 *

 * The formula used is relatively simple and documented inline in the

 * function. The main rationale is that we want to select a good task

 * to kill when we run out of memory.

 *

 * Good in this context means that:

 * 1) we lose the minimum amount of work done

 * 2) we recover a large amount of memory

 * 3) we don't kill anything innocent of eating tons of memory

 * 4) we want to kill the minimum amount of processes (one)

 * 5) we try to kill the process the user expects us to kill, this

 *    algorithm has been meticulously tuned to meet the principle

 *    of least surprise ... (be careful when you change it)

 */

unsigned long badness(struct task_struct *p, unsigned long uptime)

{

        unsigned long points, cpu_time, run_time, s;

        struct mm_struct *mm;

        struct task_struct *child;

        task_lock(p);

        mm = p->mm;

        if (!mm) {

                task_unlock(p);

                return 0;

        }

        /*

         * The memory size of the process is the basis for the badness.

         */

        points = mm->total_vm;

        /*

         * After this unlock we can no longer dereference local variable `mm'

         */

        task_unlock(p);

        /*

         * swapoff can easily use up all memory, so kill those first.

         */

        if (p->flags & PF_SWAPOFF)

                return ULONG_MAX;

        /*

         * Processes which fork a lot of child processes are likely

         * a good choice. We add half the vmsize of the children if they

         * have an own mm. This prevents forking servers to flood the

         * machine with an endless amount of children. In case a single

         * child is eating the vast majority of memory, adding only half

         * to the parents will make the child our kill candidate of choice.

         */

        list_for_each_entry(child, &p->children, sibling) {

                task_lock(child);

                if (child->mm != mm && child->mm)

                        points += child->mm->total_vm/2 + 1;

                task_unlock(child);

        }

        /*

         * CPU time is in tens of seconds and run time is in thousands

         * of seconds. There is no particular reason for this other than

         * that it turned out to work very well in practice.

         */

        cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))

                >> (SHIFT_HZ + 3);

        if (uptime >= p->start_time.tv_sec)

                run_time = (uptime - p->start_time.tv_sec) >> 10;

        else

                run_time = 0;

        s = int_sqrt(cpu_time);

        if (s)

                points /= s;

        s = int_sqrt(int_sqrt(run_time));

        if (s)

                points /= s;

        /*

         * Niced processes are most likely less important, so double

         * their badness points.

         */

        if (task_nice(p) > 0)

                points *= 2;

        /*

         * Superuser processes are usually more important, so we make it

         * less likely that we kill those.

         */

        if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||

                                p->uid == 0 || p->euid == 0)

                points /= 4;

        /*

         * We don't want to kill a process with direct hardware access.

         * Not only could that mess up the hardware, but usually users

         * tend to only have this flag set on applications they think

         * of as important.

         */

        if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))

                points /= 4;

        /*

         * If p's nodes don't overlap ours, it may still help to kill p

         * because p may have allocated or otherwise mapped memory on

         * this node before. However it will be less likely.

         */

        if (!cpuset_mems_allowed_intersects(current, p))

                points /= 8;

        /*

         * Adjust the score by oomkilladj.

         */

        if (p->oomkilladj) {

                if (p->oomkilladj > 0) {

                        if (!points)

                                points = 1;

                        points <<= p->oomkilladj;

                } else

                        points >>= -(p->oomkilladj);

        }

#ifdef DEBUG

        printk(KERN_DEBUG "OOMkill: task %d (%s) got %lu points\n",

        p->pid, p->comm, points);

#endif

        return points;

}

/*

 * Determine the type of allocation constraint.

 */

static inline enum oom_constraint constrained_alloc(struct zonelist *zonelist,

                                                    gfp_t gfp_mask)

{

#ifdef CONFIG_NUMA

        struct zone **z;

        nodemask_t nodes = node_states[N_HIGH_MEMORY];

        for (z = zonelist->zones; *z; z++)

                if (cpuset_zone_allowed_softwall(*z, gfp_mask))

                        node_clear(zone_to_nid(*z), nodes);

                else

                        return CONSTRAINT_CPUSET;

        if (!nodes_empty(nodes))

                return CONSTRAINT_MEMORY_POLICY;

#endif

        return CONSTRAINT_NONE;

}

/*

 * Simple selection loop. We chose the process with the highest

 * number of 'points'. We expect the caller will lock the tasklist.

 *

 * (not docbooked, we don't want this one cluttering up the manual)

 */

static struct task_struct *select_bad_process(unsigned long *ppoints)

{

        struct task_struct *g, *p;

        struct task_struct *chosen = NULL;

        struct timespec uptime;

        *ppoints = 0;

        do_posix_clock_monotonic_gettime(&uptime);

        do_each_thread(g, p) {

                unsigned long points;

                /*

                 * skip kernel threads and tasks which have already released

                 * their mm.

                 */

                if (!p->mm)

                        continue;

                /* skip the init task */

                if (is_global_init(p))

                        continue;

                /*

                 * This task already has access to memory reserves and is

                 * being killed. Don't allow any other task access to the

                 * memory reserve.

                 *

                 * Note: this may have a chance of deadlock if it gets

                 * blocked waiting for another task which itself is waiting

                 * for memory. Is there a better alternative?

                 */

                if (test_tsk_thread_flag(p, TIF_MEMDIE))

                        return ERR_PTR(-1UL);

                /*

                 * This is in the process of releasing memory so wait for it

                 * to finish before killing some other task by mistake.

                 *

                 * However, if p is the current task, we allow the 'kill' to

                 * go ahead if it is exiting: this will simply set TIF_MEMDIE,

                 * which will allow it to gain access to memory reserves in

                 * the process of exiting and releasing its resources.

                 * Otherwise we could get an easy OOM deadlock.

                 */

                if (p->flags & PF_EXITING) {

                        if (p != current)

                                return ERR_PTR(-1UL);

                        chosen = p;

                        *ppoints = ULONG_MAX;

                }

                if (p->oomkilladj == OOM_DISABLE)

                        continue;

                points = badness(p, uptime.tv_sec);

                if (points > *ppoints || !chosen) {

                        chosen = p;

                        *ppoints = points;

                }

        } while_each_thread(g, p);

        return chosen;

}

/**

 * Send SIGKILL to the selected  process irrespective of  CAP_SYS_RAW_IO

 * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO

 * set.

 */

static void __oom_kill_task(struct task_struct *p, int verbose)

{

        if (is_global_init(p)) {

                WARN_ON(1);

                printk(KERN_WARNING "tried to kill init!\n");

                return;

        }

        if (!p->mm) {

                WARN_ON(1);

                printk(KERN_WARNING "tried to kill an mm-less task!\n");

                return;

        }

        if (verbose)

                printk(KERN_ERR "Killed process %d (%s)\n",

                                task_pid_nr(p), p->comm);

        /*

         * We give our sacrificial lamb high priority and access to

         * all the memory it needs. That way it should be able to

         * exit() and clear out its resources quickly...

         */

        p->time_slice = HZ;

        set_tsk_thread_flag(p, TIF_MEMDIE);

        force_sig(SIGKILL, p);

}

static int oom_kill_task(struct task_struct *p)

{

        struct mm_struct *mm;

        struct task_struct *g, *q;

        mm = p->mm;

        /* WARNING: mm may not be dereferenced since we did not obtain its

         * value from get_task_mm(p).  This is OK since all we need to do is

         * compare mm to q->mm below.

         *

         * Furthermore, even if mm contains a non-NULL value, p->mm may

         * change to NULL at any time since we do not hold task_lock(p).

         * However, this is of no concern to us.

         */

        if (mm == NULL)

                return 1;

        /*

         * Don't kill the process if any threads are set to OOM_DISABLE

         */

        do_each_thread(g, q) {

                if (q->mm == mm && q->oomkilladj == OOM_DISABLE)

                        return 1;

        } while_each_thread(g, q);

        __oom_kill_task(p, 1);

        /*

         * kill all processes that share the ->mm (i.e. all threads),

         * but are in a different thread group. Don't let them have access

         * to memory reserves though, otherwise we might deplete all memory.

         */

        do_each_thread(g, q) {

                if (q->mm == mm && !same_thread_group(q, p))

                        force_sig(SIGKILL, q);

        } while_each_thread(g, q);

        return 0;

}

static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,

                            unsigned long points, const char *message)

{

        struct task_struct *c;

        if (printk_ratelimit()) {

                printk(KERN_WARNING "%s invoked oom-killer: "

                        "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",

                        current->comm, gfp_mask, order, current->oomkilladj);

                dump_stack();

                show_mem();

        }

        /*

         * If the task is already exiting, don't alarm the sysadmin or kill

         * its children or threads, just set TIF_MEMDIE so it can die quickly

         */

        if (p->flags & PF_EXITING) {

                __oom_kill_task(p, 0);

                return 0;

        }

        printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",

                                        message, task_pid_nr(p), p->comm, points);

        /* Try to kill a child first */

        list_for_each_entry(c, &p->children, sibling) {

                if (c->mm == p->mm)

                        continue;

                if (!oom_kill_task(c))

                        return 0;

        }

        return oom_kill_task(p);

}

static BLOCKING_NOTIFIER_HEAD(oom_notify_list);

int register_oom_notifier(struct notifier_block *nb)

{

        return blocking_notifier_chain_register(&oom_notify_list, nb);

}

EXPORT_SYMBOL_GPL(register_oom_notifier);

int unregister_oom_notifier(struct notifier_block *nb)

{

        return blocking_notifier_chain_unregister(&oom_notify_list, nb);

}

EXPORT_SYMBOL_GPL(unregister_oom_notifier);

/*

 * Try to acquire the OOM killer lock for the zones in zonelist.  Returns zero

 * if a parallel OOM killing is already taking place that includes a zone in

 * the zonelist.  Otherwise, locks all zones in the zonelist and returns 1.

 */

int try_set_zone_oom(struct zonelist *zonelist)

{

        struct zone **z;

        int ret = 1;

        z = zonelist->zones;

        spin_lock(&zone_scan_mutex);

        do {

                if (zone_is_oom_locked(*z)) {

                        ret = 0;

                        goto out;

                }

        } while (*(++z) != NULL);

        /*

         * Lock each zone in the zonelist under zone_scan_mutex so a parallel

         * invocation of try_set_zone_oom() doesn't succeed when it shouldn't.

         */

        z = zonelist->zones;

        do {

                zone_set_flag(*z, ZONE_OOM_LOCKED);

        } while (*(++z) != NULL);

out:

        spin_unlock(&zone_scan_mutex);

        return ret;

}

/*

 * Clears the ZONE_OOM_LOCKED flag for all zones in the zonelist so that failed

 * allocation attempts with zonelists containing them may now recall the OOM

 * killer, if necessary.

 */

void clear_zonelist_oom(struct zonelist *zonelist)

{

        struct zone **z;

        z = zonelist->zones;

        spin_lock(&zone_scan_mutex);

        do {

                zone_clear_flag(*z, ZONE_OOM_LOCKED);

        } while (*(++z) != NULL);

        spin_unlock(&zone_scan_mutex);

}

/**

 * out_of_memory - kill the "best" process when we run out of memory

 *

 * If we run out of memory, we have the choice between either

 * killing a random task (bad), letting the system crash (worse)

 * OR try to be smart about which process to kill. Note that we

 * don't have to be perfect here, we just have to be good.

 */

void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)

{

        struct task_struct *p;

        unsigned long points = 0;

        unsigned long freed = 0;

        enum oom_constraint constraint;

        blocking_notifier_call_chain(&oom_notify_list, 0, &freed);

        if (freed > 0)

                /* Got some memory back in the last second. */

                return;

        if (sysctl_panic_on_oom == 2)

                panic("out of memory. Compulsory panic_on_oom is selected.\n");

        /*

         * Check if there were limitations on the allocation (only relevant for

         * NUMA) that may require different handling.

         */

        constraint = constrained_alloc(zonelist, gfp_mask);

        read_lock(&tasklist_lock);

        switch (constraint) {

        case CONSTRAINT_MEMORY_POLICY:

                oom_kill_process(current, gfp_mask, order, points,

                                "No available memory (MPOL_BIND)");

                break;

        case CONSTRAINT_NONE:

                if (sysctl_panic_on_oom)

                        panic("out of memory. panic_on_oom is selected\n");

                /* Fall-through */

        case CONSTRAINT_CPUSET:

                if (sysctl_oom_kill_allocating_task) {

                        oom_kill_process(current, gfp_mask, order, points,

                                        "Out of memory (oom_kill_allocating_task)");

                        break;

                }

retry:

                /*

                 * Rambo mode: Shoot down a process and hope it solves whatever

                 * issues we may have.

                 */

                p = select_bad_process(&points);

                if (PTR_ERR(p) == -1UL)

                        goto out;

                /* Found nothing?!?! Either we hang forever, or we panic. */

                if (!p) {

                        read_unlock(&tasklist_lock);

                        panic("Out of memory and no killable processes...\n");

                }

                if (oom_kill_process(p, gfp_mask, order, points,

                                     "Out of memory"))

                        goto retry;

                break;

        }

out:

        read_unlock(&tasklist_lock);

        /*

         * Give "p" a good chance of killing itself before we

         * retry to allocate memory unless "p" is current

         */

        if (!test_thread_flag(TIF_MEMDIE))

                schedule_timeout_uninterruptible(1);

}