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    SubjectRe: [v6,1/2] pid: Replace pid bitmap implementation with IDR API
    Hi Gargi,

    This patch breaks CRIU, because it changes a meaning of ns_last_pid.

    ========================== Run zdtm/static/env00 in h ==========================
    DEP env00.d
    CC env00.o
    LINK env00
    Start test
    ./env00 --pidfile=env00.pid --outfile=env00.out --envname=ENV_00_TEST
    Run criu dump
    Run criu restore
    =[log]=> dump/zdtm/static/env00/52/1/restore.log
    ------------------------ grep Error ------------------------
    (00.000587) No mountpoints-6.img image
    (00.000593) mnt: Reading mountpoint images (id 6 pid 52)
    (00.000653) Forking task with 52 pid (flags 0x0)
    (00.007568) PID: real 51 virt 52
    (00.010363) 52: Error (criu/cr-restore.c:1787): Pid 51 do not match expected 52 (task 52)
    (00.010474) Error (criu/cr-restore.c:2449): Restoring FAILED.
    ------------------------ ERROR OVER ------------------------

    Before this patch, ns_last_pid contains a pid of a last process. With
    this patch, it contains a pid of a "next" process.

    In CRIU we use ns_last_pid to restore a process with a specified pid,
    and now this logic is broken:

    $ uname -a
    Linux laptop 4.11.11-200.fc25.x86_64 #1 SMP Mon Jul 17 17:41:12 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
    $ echo 19999 > /proc/sys/kernel/ns_last_pid && sh -c 'echo $$'
    20000

    $ uname -a
    Linux fc24 4.14.0-rc5-next-20171018 #1 SMP Wed Oct 18 23:52:43 PDT 2017 x86_64 x86_64 x86_64 GNU/Linux
    $ echo 19999 > /proc/sys/kernel/ns_last_pid && sh -c 'echo $$'
    19999

    Thanks,
    Andrei

    On Wed, Oct 11, 2017 at 06:19:38PM -0400, Gargi Sharma wrote:
    > This patch replaces the current bitmap implemetation for
    > Process ID allocation. Functions that are no longer required,
    > for example, free_pidmap(), alloc_pidmap(), etc. are removed.
    > The rest of the functions are modified to use the IDR API.
    > The change was made to make the PID allocation less complex by
    > replacing custom code with calls to generic API.
    >
    > Signed-off-by: Gargi Sharma <gs051095@gmail.com>
    > Reviewed-by: Rik van Riel <riel@redhat.com>
    > ---
    > arch/powerpc/platforms/cell/spufs/sched.c | 2 +-
    > fs/proc/loadavg.c | 2 +-
    > include/linux/pid_namespace.h | 14 +--
    > init/main.c | 2 +-
    > kernel/pid.c | 201 ++++++------------------------
    > kernel/pid_namespace.c | 44 +++----
    > 6 files changed, 57 insertions(+), 208 deletions(-)
    >
    > diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c
    > index 1fbb5da..e47761c 100644
    > --- a/arch/powerpc/platforms/cell/spufs/sched.c
    > +++ b/arch/powerpc/platforms/cell/spufs/sched.c
    > @@ -1093,7 +1093,7 @@ static int show_spu_loadavg(struct seq_file *s, void *private)
    > LOAD_INT(c), LOAD_FRAC(c),
    > count_active_contexts(),
    > atomic_read(&nr_spu_contexts),
    > - task_active_pid_ns(current)->last_pid);
    > + idr_get_cursor(&task_active_pid_ns(current)->idr));
    > return 0;
    > }
    >
    > diff --git a/fs/proc/loadavg.c b/fs/proc/loadavg.c
    > index 983fce5..ba3d0e2 100644
    > --- a/fs/proc/loadavg.c
    > +++ b/fs/proc/loadavg.c
    > @@ -23,7 +23,7 @@ static int loadavg_proc_show(struct seq_file *m, void *v)
    > LOAD_INT(avnrun[1]), LOAD_FRAC(avnrun[1]),
    > LOAD_INT(avnrun[2]), LOAD_FRAC(avnrun[2]),
    > nr_running(), nr_threads,
    > - task_active_pid_ns(current)->last_pid);
    > + idr_get_cursor(&task_active_pid_ns(current)->idr));
    > return 0;
    > }
    >
    > diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
    > index b09136f..f4db4a7 100644
    > --- a/include/linux/pid_namespace.h
    > +++ b/include/linux/pid_namespace.h
    > @@ -9,15 +9,8 @@
    > #include <linux/nsproxy.h>
    > #include <linux/kref.h>
    > #include <linux/ns_common.h>
    > +#include <linux/idr.h>
    >
    > -struct pidmap {
    > - atomic_t nr_free;
    > - void *page;
    > -};
    > -
    > -#define BITS_PER_PAGE (PAGE_SIZE * 8)
    > -#define BITS_PER_PAGE_MASK (BITS_PER_PAGE-1)
    > -#define PIDMAP_ENTRIES ((PID_MAX_LIMIT+BITS_PER_PAGE-1)/BITS_PER_PAGE)
    >
    > struct fs_pin;
    >
    > @@ -29,9 +22,8 @@ enum { /* definitions for pid_namespace's hide_pid field */
    >
    > struct pid_namespace {
    > struct kref kref;
    > - struct pidmap pidmap[PIDMAP_ENTRIES];
    > + struct idr idr;
    > struct rcu_head rcu;
    > - int last_pid;
    > unsigned int nr_hashed;
    > struct task_struct *child_reaper;
    > struct kmem_cache *pid_cachep;
    > @@ -105,6 +97,6 @@ static inline int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
    >
    > extern struct pid_namespace *task_active_pid_ns(struct task_struct *tsk);
    > void pidhash_init(void);
    > -void pidmap_init(void);
    > +void pid_idr_init(void);
    >
    > #endif /* _LINUX_PID_NS_H */
    > diff --git a/init/main.c b/init/main.c
    > index 0ee9c686..9f4db20 100644
    > --- a/init/main.c
    > +++ b/init/main.c
    > @@ -667,7 +667,7 @@ asmlinkage __visible void __init start_kernel(void)
    > if (late_time_init)
    > late_time_init();
    > calibrate_delay();
    > - pidmap_init();
    > + pid_idr_init();
    > anon_vma_init();
    > acpi_early_init();
    > #ifdef CONFIG_X86
    > diff --git a/kernel/pid.c b/kernel/pid.c
    > index 020dedb..0ce5936 100644
    > --- a/kernel/pid.c
    > +++ b/kernel/pid.c
    > @@ -39,6 +39,7 @@
    > #include <linux/proc_ns.h>
    > #include <linux/proc_fs.h>
    > #include <linux/sched/task.h>
    > +#include <linux/idr.h>
    >
    > #define pid_hashfn(nr, ns) \
    > hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
    > @@ -53,14 +54,6 @@ int pid_max = PID_MAX_DEFAULT;
    > int pid_max_min = RESERVED_PIDS + 1;
    > int pid_max_max = PID_MAX_LIMIT;
    >
    > -static inline int mk_pid(struct pid_namespace *pid_ns,
    > - struct pidmap *map, int off)
    > -{
    > - return (map - pid_ns->pidmap)*BITS_PER_PAGE + off;
    > -}
    > -
    > -#define find_next_offset(map, off) \
    > - find_next_zero_bit((map)->page, BITS_PER_PAGE, off)
    >
    > /*
    > * PID-map pages start out as NULL, they get allocated upon
    > @@ -70,10 +63,7 @@ static inline int mk_pid(struct pid_namespace *pid_ns,
    > */
    > struct pid_namespace init_pid_ns = {
    > .kref = KREF_INIT(2),
    > - .pidmap = {
    > - [ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL }
    > - },
    > - .last_pid = 0,
    > + .idr = IDR_INIT,
    > .nr_hashed = PIDNS_HASH_ADDING,
    > .level = 0,
    > .child_reaper = &init_task,
    > @@ -101,138 +91,6 @@ EXPORT_SYMBOL_GPL(init_pid_ns);
    >
    > static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
    >
    > -static void free_pidmap(struct upid *upid)
    > -{
    > - int nr = upid->nr;
    > - struct pidmap *map = upid->ns->pidmap + nr / BITS_PER_PAGE;
    > - int offset = nr & BITS_PER_PAGE_MASK;
    > -
    > - clear_bit(offset, map->page);
    > - atomic_inc(&map->nr_free);
    > -}
    > -
    > -/*
    > - * If we started walking pids at 'base', is 'a' seen before 'b'?
    > - */
    > -static int pid_before(int base, int a, int b)
    > -{
    > - /*
    > - * This is the same as saying
    > - *
    > - * (a - base + MAXUINT) % MAXUINT < (b - base + MAXUINT) % MAXUINT
    > - * and that mapping orders 'a' and 'b' with respect to 'base'.
    > - */
    > - return (unsigned)(a - base) < (unsigned)(b - base);
    > -}
    > -
    > -/*
    > - * We might be racing with someone else trying to set pid_ns->last_pid
    > - * at the pid allocation time (there's also a sysctl for this, but racing
    > - * with this one is OK, see comment in kernel/pid_namespace.c about it).
    > - * We want the winner to have the "later" value, because if the
    > - * "earlier" value prevails, then a pid may get reused immediately.
    > - *
    > - * Since pids rollover, it is not sufficient to just pick the bigger
    > - * value. We have to consider where we started counting from.
    > - *
    > - * 'base' is the value of pid_ns->last_pid that we observed when
    > - * we started looking for a pid.
    > - *
    > - * 'pid' is the pid that we eventually found.
    > - */
    > -static void set_last_pid(struct pid_namespace *pid_ns, int base, int pid)
    > -{
    > - int prev;
    > - int last_write = base;
    > - do {
    > - prev = last_write;
    > - last_write = cmpxchg(&pid_ns->last_pid, prev, pid);
    > - } while ((prev != last_write) && (pid_before(base, last_write, pid)));
    > -}
    > -
    > -static int alloc_pidmap(struct pid_namespace *pid_ns)
    > -{
    > - int i, offset, max_scan, pid, last = pid_ns->last_pid;
    > - struct pidmap *map;
    > -
    > - pid = last + 1;
    > - if (pid >= pid_max)
    > - pid = RESERVED_PIDS;
    > - offset = pid & BITS_PER_PAGE_MASK;
    > - map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
    > - /*
    > - * If last_pid points into the middle of the map->page we
    > - * want to scan this bitmap block twice, the second time
    > - * we start with offset == 0 (or RESERVED_PIDS).
    > - */
    > - max_scan = DIV_ROUND_UP(pid_max, BITS_PER_PAGE) - !offset;
    > - for (i = 0; i <= max_scan; ++i) {
    > - if (unlikely(!map->page)) {
    > - void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
    > - /*
    > - * Free the page if someone raced with us
    > - * installing it:
    > - */
    > - spin_lock_irq(&pidmap_lock);
    > - if (!map->page) {
    > - map->page = page;
    > - page = NULL;
    > - }
    > - spin_unlock_irq(&pidmap_lock);
    > - kfree(page);
    > - if (unlikely(!map->page))
    > - return -ENOMEM;
    > - }
    > - if (likely(atomic_read(&map->nr_free))) {
    > - for ( ; ; ) {
    > - if (!test_and_set_bit(offset, map->page)) {
    > - atomic_dec(&map->nr_free);
    > - set_last_pid(pid_ns, last, pid);
    > - return pid;
    > - }
    > - offset = find_next_offset(map, offset);
    > - if (offset >= BITS_PER_PAGE)
    > - break;
    > - pid = mk_pid(pid_ns, map, offset);
    > - if (pid >= pid_max)
    > - break;
    > - }
    > - }
    > - if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
    > - ++map;
    > - offset = 0;
    > - } else {
    > - map = &pid_ns->pidmap[0];
    > - offset = RESERVED_PIDS;
    > - if (unlikely(last == offset))
    > - break;
    > - }
    > - pid = mk_pid(pid_ns, map, offset);
    > - }
    > - return -EAGAIN;
    > -}
    > -
    > -int next_pidmap(struct pid_namespace *pid_ns, unsigned int last)
    > -{
    > - int offset;
    > - struct pidmap *map, *end;
    > -
    > - if (last >= PID_MAX_LIMIT)
    > - return -1;
    > -
    > - offset = (last + 1) & BITS_PER_PAGE_MASK;
    > - map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];
    > - end = &pid_ns->pidmap[PIDMAP_ENTRIES];
    > - for (; map < end; map++, offset = 0) {
    > - if (unlikely(!map->page))
    > - continue;
    > - offset = find_next_bit((map)->page, BITS_PER_PAGE, offset);
    > - if (offset < BITS_PER_PAGE)
    > - return mk_pid(pid_ns, map, offset);
    > - }
    > - return -1;
    > -}
    > -
    > void put_pid(struct pid *pid)
    > {
    > struct pid_namespace *ns;
    > @@ -266,7 +124,7 @@ void free_pid(struct pid *pid)
    > struct upid *upid = pid->numbers + i;
    > struct pid_namespace *ns = upid->ns;
    > hlist_del_rcu(&upid->pid_chain);
    > - switch(--ns->nr_hashed) {
    > + switch (--ns->nr_hashed) {
    > case 2:
    > case 1:
    > /* When all that is left in the pid namespace
    > @@ -284,12 +142,11 @@ void free_pid(struct pid *pid)
    > schedule_work(&ns->proc_work);
    > break;
    > }
    > +
    > + idr_remove(&ns->idr, upid->nr);
    > }
    > spin_unlock_irqrestore(&pidmap_lock, flags);
    >
    > - for (i = 0; i <= pid->level; i++)
    > - free_pidmap(pid->numbers + i);
    > -
    > call_rcu(&pid->rcu, delayed_put_pid);
    > }
    >
    > @@ -308,8 +165,29 @@ struct pid *alloc_pid(struct pid_namespace *ns)
    >
    > tmp = ns;
    > pid->level = ns->level;
    > +
    > for (i = ns->level; i >= 0; i--) {
    > - nr = alloc_pidmap(tmp);
    > + int pid_min = 1;
    > +
    > + idr_preload(GFP_KERNEL);
    > + spin_lock_irq(&pidmap_lock);
    > +
    > + /*
    > + * init really needs pid 1, but after reaching the maximum
    > + * wrap back to RESERVED_PIDS
    > + */
    > + if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
    > + pid_min = RESERVED_PIDS;
    > +
    > + /*
    > + * Store a null pointer so find_pid_ns does not find
    > + * a partially initialized PID (see below).
    > + */
    > + nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
    > + pid_max, GFP_ATOMIC);
    > + spin_unlock_irq(&pidmap_lock);
    > + idr_preload_end();
    > +
    > if (nr < 0) {
    > retval = nr;
    > goto out_free;
    > @@ -339,6 +217,8 @@ struct pid *alloc_pid(struct pid_namespace *ns)
    > for ( ; upid >= pid->numbers; --upid) {
    > hlist_add_head_rcu(&upid->pid_chain,
    > &pid_hash[pid_hashfn(upid->nr, upid->ns)]);
    > + /* Make the PID visible to find_pid_ns. */
    > + idr_replace(&upid->ns->idr, pid, upid->nr);
    > upid->ns->nr_hashed++;
    > }
    > spin_unlock_irq(&pidmap_lock);
    > @@ -350,8 +230,11 @@ struct pid *alloc_pid(struct pid_namespace *ns)
    > put_pid_ns(ns);
    >
    > out_free:
    > + spin_lock_irq(&pidmap_lock);
    > while (++i <= ns->level)
    > - free_pidmap(pid->numbers + i);
    > + idr_remove(&ns->idr, (pid->numbers + i)->nr);
    > +
    > + spin_unlock_irq(&pidmap_lock);
    >
    > kmem_cache_free(ns->pid_cachep, pid);
    > return ERR_PTR(retval);
    > @@ -553,16 +436,7 @@ EXPORT_SYMBOL_GPL(task_active_pid_ns);
    > */
    > struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
    > {
    > - struct pid *pid;
    > -
    > - do {
    > - pid = find_pid_ns(nr, ns);
    > - if (pid)
    > - break;
    > - nr = next_pidmap(ns, nr);
    > - } while (nr > 0);
    > -
    > - return pid;
    > + return idr_get_next(&ns->idr, &nr);
    > }
    >
    > /*
    > @@ -578,7 +452,7 @@ void __init pidhash_init(void)
    > 0, 4096);
    > }
    >
    > -void __init pidmap_init(void)
    > +void __init pid_idr_init(void)
    > {
    > /* Verify no one has done anything silly: */
    > BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_HASH_ADDING);
    > @@ -590,10 +464,7 @@ void __init pidmap_init(void)
    > PIDS_PER_CPU_MIN * num_possible_cpus());
    > pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
    >
    > - init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
    > - /* Reserve PID 0. We never call free_pidmap(0) */
    > - set_bit(0, init_pid_ns.pidmap[0].page);
    > - atomic_dec(&init_pid_ns.pidmap[0].nr_free);
    > + idr_init(&init_pid_ns.idr);
    >
    > init_pid_ns.pid_cachep = KMEM_CACHE(pid,
    > SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT);
    > diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
    > index 4918314..5009dbe 100644
    > --- a/kernel/pid_namespace.c
    > +++ b/kernel/pid_namespace.c
    > @@ -21,6 +21,7 @@
    > #include <linux/export.h>
    > #include <linux/sched/task.h>
    > #include <linux/sched/signal.h>
    > +#include <linux/idr.h>
    >
    > struct pid_cache {
    > int nr_ids;
    > @@ -98,7 +99,6 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
    > struct pid_namespace *ns;
    > unsigned int level = parent_pid_ns->level + 1;
    > struct ucounts *ucounts;
    > - int i;
    > int err;
    >
    > err = -EINVAL;
    > @@ -117,17 +117,15 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
    > if (ns == NULL)
    > goto out_dec;
    >
    > - ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
    > - if (!ns->pidmap[0].page)
    > - goto out_free;
    > + idr_init(&ns->idr);
    >
    > ns->pid_cachep = create_pid_cachep(level + 1);
    > if (ns->pid_cachep == NULL)
    > - goto out_free_map;
    > + goto out_free_idr;
    >
    > err = ns_alloc_inum(&ns->ns);
    > if (err)
    > - goto out_free_map;
    > + goto out_free_idr;
    > ns->ns.ops = &pidns_operations;
    >
    > kref_init(&ns->kref);
    > @@ -138,17 +136,10 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
    > ns->nr_hashed = PIDNS_HASH_ADDING;
    > INIT_WORK(&ns->proc_work, proc_cleanup_work);
    >
    > - set_bit(0, ns->pidmap[0].page);
    > - atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
    > -
    > - for (i = 1; i < PIDMAP_ENTRIES; i++)
    > - atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
    > -
    > return ns;
    >
    > -out_free_map:
    > - kfree(ns->pidmap[0].page);
    > -out_free:
    > +out_free_idr:
    > + idr_destroy(&ns->idr);
    > kmem_cache_free(pid_ns_cachep, ns);
    > out_dec:
    > dec_pid_namespaces(ucounts);
    > @@ -168,11 +159,9 @@ static void delayed_free_pidns(struct rcu_head *p)
    >
    > static void destroy_pid_namespace(struct pid_namespace *ns)
    > {
    > - int i;
    > -
    > ns_free_inum(&ns->ns);
    > - for (i = 0; i < PIDMAP_ENTRIES; i++)
    > - kfree(ns->pidmap[i].page);
    > +
    > + idr_destroy(&ns->idr);
    > call_rcu(&ns->rcu, delayed_free_pidns);
    > }
    >
    > @@ -213,6 +202,7 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
    > int rc;
    > struct task_struct *task, *me = current;
    > int init_pids = thread_group_leader(me) ? 1 : 2;
    > + struct pid *pid;
    >
    > /* Don't allow any more processes into the pid namespace */
    > disable_pid_allocation(pid_ns);
    > @@ -239,20 +229,16 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
    > * maintain a tasklist for each pid namespace.
    > *
    > */
    > + rcu_read_lock();
    > read_lock(&tasklist_lock);
    > - nr = next_pidmap(pid_ns, 1);
    > - while (nr > 0) {
    > - rcu_read_lock();
    > -
    > - task = pid_task(find_vpid(nr), PIDTYPE_PID);
    > + nr = 2;
    > + idr_for_each_entry_continue(&pid_ns->idr, pid, nr) {
    > + task = pid_task(pid, PIDTYPE_PID);
    > if (task && !__fatal_signal_pending(task))
    > send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
    > -
    > - rcu_read_unlock();
    > -
    > - nr = next_pidmap(pid_ns, nr);
    > }
    > read_unlock(&tasklist_lock);
    > + rcu_read_unlock();
    >
    > /*
    > * Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
    > @@ -311,7 +297,7 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
    > * it should synchronize its usage with external means.
    > */
    >
    > - tmp.data = &pid_ns->last_pid;
    > + tmp.data = &pid_ns->idr.idr_next;
    > return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
    > }
    >

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