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Date: Mon, 12 Dec 2022 09:47:08 +0800
From: Ian Kent <ikent@...hat.com>
To: Brian Foster <bfoster@...hat.com>, linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: onestero@...hat.com, willy@...radead.org, ebiederm@...hat.com
Subject: Re: [PATCH v3 3/5] pid: switch pid_namespace from idr to xarray
On 3/12/22 01:16, Brian Foster wrote:
> Switch struct pid[_namespace] management over to use the xarray api
> directly instead of the idr. The underlying data structures used by
> both interfaces is the same. The difference is that the idr api
> relies on the old, idr-custom radix-tree implementation for things
> like efficient tracking/allocation of free ids. The xarray already
> supports this, so most of this is a direct switchover from the old
> api to the new.
>
> Signed-off-by: Matthew Wilcox <willy@...radead.org>
> Signed-off-by: Brian Foster <bfoster@...hat.com>
Reviewed-by: Ian Kent <raven@...maw.net>
> ---
> include/linux/pid_namespace.h | 8 ++--
> include/linux/threads.h | 2 +-
> init/main.c | 3 +-
> kernel/pid.c | 78 ++++++++++++++++-------------------
> kernel/pid_namespace.c | 19 ++++-----
> 5 files changed, 51 insertions(+), 59 deletions(-)
>
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index 82c72482019d..e4f5979b482b 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -9,7 +9,7 @@
> #include <linux/threads.h>
> #include <linux/nsproxy.h>
> #include <linux/ns_common.h>
> -#include <linux/idr.h>
> +#include <linux/xarray.h>
>
> /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
> #define MAX_PID_NS_LEVEL 32
> @@ -17,7 +17,7 @@
> struct fs_pin;
>
> struct pid_namespace {
> - struct idr idr;
> + struct xarray xa;
> unsigned int pid_next;
> struct rcu_head rcu;
> unsigned int pid_allocated;
> @@ -38,6 +38,8 @@ extern struct pid_namespace init_pid_ns;
>
> #define PIDNS_ADDING (1U << 31)
>
> +#define PID_XA_FLAGS (XA_FLAGS_TRACK_FREE | XA_FLAGS_LOCK_IRQ)
> +
> #ifdef CONFIG_PID_NS
> static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
> {
> @@ -85,7 +87,7 @@ 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 pid_idr_init(void);
> +void pid_init(void);
>
> static inline bool task_is_in_init_pid_ns(struct task_struct *tsk)
> {
> diff --git a/include/linux/threads.h b/include/linux/threads.h
> index c34173e6c5f1..37e4391ee89f 100644
> --- a/include/linux/threads.h
> +++ b/include/linux/threads.h
> @@ -38,7 +38,7 @@
> * Define a minimum number of pids per cpu. Heuristically based
> * on original pid max of 32k for 32 cpus. Also, increase the
> * minimum settable value for pid_max on the running system based
> - * on similar defaults. See kernel/pid.c:pid_idr_init() for details.
> + * on similar defaults. See kernel/pid.c:pid_init() for details.
> */
> #define PIDS_PER_CPU_DEFAULT 1024
> #define PIDS_PER_CPU_MIN 8
> diff --git a/init/main.c b/init/main.c
> index aa21add5f7c5..7dd8888036c7 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -74,7 +74,6 @@
> #include <linux/sched.h>
> #include <linux/sched/init.h>
> #include <linux/signal.h>
> -#include <linux/idr.h>
> #include <linux/kgdb.h>
> #include <linux/ftrace.h>
> #include <linux/async.h>
> @@ -1108,7 +1107,7 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
> late_time_init();
> sched_clock_init();
> calibrate_delay();
> - pid_idr_init();
> + pid_init();
> anon_vma_init();
> #ifdef CONFIG_X86
> if (efi_enabled(EFI_RUNTIME_SERVICES))
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 2e2d33273c8e..53db06f9882d 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -41,7 +41,7 @@
> #include <linux/anon_inodes.h>
> #include <linux/sched/signal.h>
> #include <linux/sched/task.h>
> -#include <linux/idr.h>
> +#include <linux/xarray.h>
> #include <net/sock.h>
> #include <uapi/linux/pidfd.h>
>
> @@ -66,15 +66,9 @@ int pid_max = PID_MAX_DEFAULT;
> int pid_max_min = RESERVED_PIDS + 1;
> int pid_max_max = PID_MAX_LIMIT;
>
> -/*
> - * PID-map pages start out as NULL, they get allocated upon
> - * first use and are never deallocated. This way a low pid_max
> - * value does not cause lots of bitmaps to be allocated, but
> - * the scheme scales to up to 4 million PIDs, runtime.
> - */
> struct pid_namespace init_pid_ns = {
> .ns.count = REFCOUNT_INIT(2),
> - .idr = IDR_INIT(init_pid_ns.idr),
> + .xa = XARRAY_INIT(init_pid_ns.xa, PID_XA_FLAGS),
> .pid_next = 0,
> .pid_allocated = PIDNS_ADDING,
> .level = 0,
> @@ -118,7 +112,7 @@ void free_pid(struct pid *pid)
> struct upid *upid = pid->numbers + i;
> struct pid_namespace *ns = upid->ns;
>
> - xa_lock_irqsave(&ns->idr.idr_rt, flags);
> + xa_lock_irqsave(&ns->xa, flags);
> switch (--ns->pid_allocated) {
> case 2:
> case 1:
> @@ -135,8 +129,8 @@ void free_pid(struct pid *pid)
> break;
> }
>
> - idr_remove(&ns->idr, upid->nr);
> - xa_unlock_irqrestore(&ns->idr.idr_rt, flags);
> + __xa_erase(&ns->xa, upid->nr);
> + xa_unlock_irqrestore(&ns->xa, flags);
> }
>
> call_rcu(&pid->rcu, delayed_put_pid);
> @@ -147,7 +141,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
> {
> struct pid *pid;
> enum pid_type type;
> - int i, nr;
> + int i;
> struct pid_namespace *tmp;
> struct upid *upid;
> int retval = -ENOMEM;
> @@ -191,18 +185,17 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
> set_tid_size--;
> }
>
> - idr_preload(GFP_KERNEL);
> - xa_lock_irq(&tmp->idr.idr_rt);
> + xa_lock_irq(&tmp->xa);
>
> if (tid) {
> - nr = idr_alloc(&tmp->idr, NULL, tid,
> - tid + 1, GFP_ATOMIC);
> + retval = __xa_insert(&tmp->xa, tid, NULL, GFP_KERNEL);
> +
> /*
> - * If ENOSPC is returned it means that the PID is
> - * alreay in use. Return EEXIST in that case.
> + * If EBUSY is returned it means that the PID is already
> + * in use. Return EEXIST in that case.
> */
> - if (nr == -ENOSPC)
> - nr = -EEXIST;
> + if (retval == -EBUSY)
> + retval = -EEXIST;
> } else {
> int pid_min = 1;
> /*
> @@ -216,19 +209,18 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
> * 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);
> - tmp->pid_next = nr + 1;
> + retval = __xa_alloc_cyclic(&tmp->xa, &tid, NULL,
> + XA_LIMIT(pid_min, pid_max),
> + &tmp->pid_next, GFP_KERNEL);
> + if (retval == -EBUSY)
> + retval = -EAGAIN;
> }
> - xa_unlock_irq(&tmp->idr.idr_rt);
> - idr_preload_end();
> + xa_unlock_irq(&tmp->xa);
>
> - if (nr < 0) {
> - retval = (nr == -ENOSPC) ? -EAGAIN : nr;
> + if (retval < 0)
> goto out_free;
> - }
>
> - pid->numbers[i].nr = nr;
> + pid->numbers[i].nr = tid;
> pid->numbers[i].ns = tmp;
> tmp = tmp->parent;
> }
> @@ -256,17 +248,17 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
> for ( ; upid >= pid->numbers; --upid) {
> tmp = upid->ns;
>
> - xa_lock_irq(&tmp->idr.idr_rt);
> + xa_lock_irq(&tmp->xa);
> if (tmp == ns && !(tmp->pid_allocated & PIDNS_ADDING)) {
> - xa_unlock_irq(&tmp->idr.idr_rt);
> + xa_unlock_irq(&tmp->xa);
> put_pid_ns(ns);
> goto out_free;
> }
>
> /* Make the PID visible to find_pid_ns. */
> - idr_replace(&tmp->idr, pid, upid->nr);
> + __xa_store(&tmp->xa, upid->nr, pid, 0);
> tmp->pid_allocated++;
> - xa_unlock_irq(&tmp->idr.idr_rt);
> + xa_unlock_irq(&tmp->xa);
> }
>
> return pid;
> @@ -276,14 +268,14 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
> upid = pid->numbers + i;
> tmp = upid->ns;
>
> - xa_lock_irq(&tmp->idr.idr_rt);
> + xa_lock_irq(&tmp->xa);
>
> /* On failure to allocate the first pid, reset the state */
> if (tmp == ns && tmp->pid_allocated == PIDNS_ADDING)
> ns->pid_next = 0;
>
> - idr_remove(&tmp->idr, upid->nr);
> - xa_unlock_irq(&tmp->idr.idr_rt);
> + __xa_erase(&tmp->xa, upid->nr);
> + xa_unlock_irq(&tmp->xa);
> }
>
> kmem_cache_free(ns->pid_cachep, pid);
> @@ -292,14 +284,14 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
>
> void disable_pid_allocation(struct pid_namespace *ns)
> {
> - xa_lock_irq(&ns->idr.idr_rt);
> + xa_lock_irq(&ns->xa);
> ns->pid_allocated &= ~PIDNS_ADDING;
> - xa_unlock_irq(&ns->idr.idr_rt);
> + xa_unlock_irq(&ns->xa);
> }
>
> struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
> {
> - return idr_find(&ns->idr, nr);
> + return xa_load(&ns->xa, nr);
> }
> EXPORT_SYMBOL_GPL(find_pid_ns);
>
> @@ -508,7 +500,9 @@ EXPORT_SYMBOL_GPL(task_active_pid_ns);
> */
> struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
> {
> - return idr_get_next(&ns->idr, &nr);
> + unsigned long index = nr;
> +
> + return xa_find(&ns->xa, &index, ULONG_MAX, XA_PRESENT);
> }
> EXPORT_SYMBOL_GPL(find_ge_pid);
>
> @@ -650,7 +644,7 @@ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
> * take it we can leave the interrupts enabled. For now it is easier to be safe
> * than to prove it can't happen.
> */
> -void __init pid_idr_init(void)
> +void __init pid_init(void)
> {
> /* Verify no one has done anything silly: */
> BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
> @@ -662,8 +656,6 @@ void __init pid_idr_init(void)
> PIDS_PER_CPU_MIN * num_possible_cpus());
> pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
>
> - 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 a53d20c5c85e..8561e01e2d01 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -22,7 +22,7 @@
> #include <linux/export.h>
> #include <linux/sched/task.h>
> #include <linux/sched/signal.h>
> -#include <linux/idr.h>
> +#include <linux/xarray.h>
>
> static DEFINE_MUTEX(pid_caches_mutex);
> static struct kmem_cache *pid_ns_cachep;
> @@ -92,15 +92,15 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
> if (ns == NULL)
> goto out_dec;
>
> - idr_init(&ns->idr);
> + xa_init_flags(&ns->xa, PID_XA_FLAGS);
>
> ns->pid_cachep = create_pid_cachep(level);
> if (ns->pid_cachep == NULL)
> - goto out_free_idr;
> + goto out_free_xa;
>
> err = ns_alloc_inum(&ns->ns);
> if (err)
> - goto out_free_idr;
> + goto out_free_xa;
> ns->ns.ops = &pidns_operations;
>
> refcount_set(&ns->ns.count, 1);
> @@ -112,8 +112,8 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
>
> return ns;
>
> -out_free_idr:
> - idr_destroy(&ns->idr);
> +out_free_xa:
> + xa_destroy(&ns->xa);
> kmem_cache_free(pid_ns_cachep, ns);
> out_dec:
> dec_pid_namespaces(ucounts);
> @@ -135,7 +135,7 @@ static void destroy_pid_namespace(struct pid_namespace *ns)
> {
> ns_free_inum(&ns->ns);
>
> - idr_destroy(&ns->idr);
> + xa_destroy(&ns->xa);
> call_rcu(&ns->rcu, delayed_free_pidns);
> }
>
> @@ -165,7 +165,7 @@ EXPORT_SYMBOL_GPL(put_pid_ns);
>
> void zap_pid_ns_processes(struct pid_namespace *pid_ns)
> {
> - int nr;
> + long nr;
> int rc;
> struct task_struct *task, *me = current;
> int init_pids = thread_group_leader(me) ? 1 : 2;
> @@ -198,8 +198,7 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
> */
> rcu_read_lock();
> read_lock(&tasklist_lock);
> - nr = 2;
> - idr_for_each_entry_continue(&pid_ns->idr, pid, nr) {
> + xa_for_each_range(&pid_ns->xa, nr, pid, 2, ULONG_MAX) {
> task = pid_task(pid, PIDTYPE_PID);
> if (task && !__fatal_signal_pending(task))
> group_send_sig_info(SIGKILL, SEND_SIG_PRIV, task, PIDTYPE_MAX);
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