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Message-ID: <4jlpjuptn5fzgrfgbct2l3dyerb3gnxwd3ujir4dodwkxivmxs@u7mptlgts2wq>
Date: Fri, 1 Nov 2024 12:51:49 +0100
From: Joel Granados <joel.granados@...nel.org>
To: Yun Zhou <yun.zhou@...driver.com>
Cc: mcgrof@...nel.org, kees@...nel.org, rostedt@...dmis.org,
mhiramat@...nel.org, mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel: add pid_max to pid_namespace
On Wed, Oct 30, 2024 at 01:29:33PM +0800, Yun Zhou wrote:
> It is necessary to have a different pid_max in different containers.
> For example, multiple containers are running on a host, one of which
> is Android, and its 32 bit bionic libc only accepts pid <= 65535. So
> it requires the global pid_max <= 65535. This will cause configuration
> conflicts with other containers and also limit the maximum number of
> tasks for the entire system.
>
> Signed-off-by: Yun Zhou <yun.zhou@...driver.com>
> ---
> include/linux/pid_namespace.h | 1 +
> kernel/pid.c | 12 +++++------
> kernel/pid_namespace.c | 35 ++++++++++++++++++++++++++-----
> kernel/sysctl.c | 9 --------
> kernel/trace/pid_list.c | 2 +-
> kernel/trace/trace.h | 2 --
> kernel/trace/trace_sched_switch.c | 2 +-
> 7 files changed, 39 insertions(+), 24 deletions(-)
>
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index f9f9931e02d6..064cfe2542fc 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -38,6 +38,7 @@ struct pid_namespace {
> struct ucounts *ucounts;
> int reboot; /* group exit code if this pidns was rebooted */
> struct ns_common ns;
> + int pid_max;
> #if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
> int memfd_noexec_scope;
> #endif
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 2715afb77eab..f8026a61436b 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -60,8 +60,6 @@ struct pid init_struct_pid = {
> }, }
> };
>
> -int pid_max = PID_MAX_DEFAULT;
> -
> int pid_max_min = RESERVED_PIDS + 1;
> int pid_max_max = PID_MAX_LIMIT;
> /*
> @@ -78,6 +76,7 @@ static u64 pidfs_ino = RESERVED_PIDS;
> */
> struct pid_namespace init_pid_ns = {
> .ns.count = REFCOUNT_INIT(2),
> + .pid_max = PID_MAX_DEFAULT,
> .idr = IDR_INIT(init_pid_ns.idr),
> .pid_allocated = PIDNS_ADDING,
> .level = 0,
> @@ -198,7 +197,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
> tid = set_tid[ns->level - i];
>
> retval = -EINVAL;
> - if (tid < 1 || tid >= pid_max)
> + if (tid < 1 || tid >= tmp->pid_max)
> goto out_free;
> /*
> * Also fail if a PID != 1 is requested and
> @@ -238,7 +237,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
> * a partially initialized PID (see below).
> */
> nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
> - pid_max, GFP_ATOMIC);
> + tmp->pid_max, GFP_ATOMIC);
> }
> spin_unlock_irq(&pidmap_lock);
> idr_preload_end();
> @@ -653,11 +652,12 @@ void __init pid_idr_init(void)
> BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_ADDING);
>
> /* bump default and minimum pid_max based on number of cpus */
> - pid_max = min(pid_max_max, max_t(int, pid_max,
> + init_pid_ns.pid_max = min(pid_max_max, max_t(int, init_pid_ns.pid_max,
> PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
> pid_max_min = max_t(int, pid_max_min,
> PIDS_PER_CPU_MIN * num_possible_cpus());
> - pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
> + pr_info("pid_max: default: %u minimum: %u\n", init_pid_ns.pid_max,
> + pid_max_min);
>
> idr_init(&init_pid_ns.idr);
>
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index d70ab49d5b4a..d8ddc0c56599 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -111,6 +111,7 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
> ns->user_ns = get_user_ns(user_ns);
> ns->ucounts = ucounts;
> ns->pid_allocated = PIDNS_ADDING;
> + ns->pid_max = parent_pid_ns->pid_max;
> #if defined(CONFIG_SYSCTL) && defined(CONFIG_MEMFD_CREATE)
> ns->memfd_noexec_scope = pidns_memfd_noexec_scope(parent_pid_ns);
> #endif
> @@ -280,19 +281,45 @@ static int pid_ns_ctl_handler(const struct ctl_table *table, int write,
>
> return ret;
> }
> +#endif /* CONFIG_CHECKPOINT_RESTORE */
> +
> +static int pid_max_ns_ctl_handler(const struct ctl_table *table, int write,
> + void *buffer, size_t *lenp, loff_t *ppos)
> +{
> + struct pid_namespace *pid_ns = task_active_pid_ns(current);
> + struct ctl_table tmp = *table;
> +
> + if (write && !checkpoint_restore_ns_capable(pid_ns->user_ns))
> + return -EPERM;
> +
> + tmp.data = &pid_ns->pid_max;
> + if (pid_ns->parent)
> + tmp.extra2 = &pid_ns->parent->pid_max;
> +
> + return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
> +}
>
> -extern int pid_max;
> static struct ctl_table pid_ns_ctl_table[] = {
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> {
> .procname = "ns_last_pid",
> .maxlen = sizeof(int),
> .mode = 0666, /* permissions are checked in the handler */
> .proc_handler = pid_ns_ctl_handler,
> .extra1 = SYSCTL_ZERO,
> - .extra2 = &pid_max,
> + .extra2 = &init_pid_ns.pid_max,
> },
> -};
> #endif /* CONFIG_CHECKPOINT_RESTORE */
> + {
> + .procname = "pid_max",
> + .maxlen = sizeof(int),
> + .mode = 0644,
> + .proc_handler = pid_max_ns_ctl_handler,
> + .extra1 = &pid_max_min,
> + .extra2 = &pid_max_max,
> + },
> + { }
There is no longer any need for sentinels in ctl_table arrays. Please
remove this one for your next version.
Best
--
Joel Granados
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