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Message-ID: <20200627234127.GA36944@carbon.DHCP.thefacebook.com>
Date: Sat, 27 Jun 2020 16:41:27 -0700
From: Roman Gushchin <guro@...com>
To: Cong Wang <xiyou.wangcong@...il.com>
CC: Cameron Berkenpas <cam@...-zeon.de>, Zefan Li <lizefan@...wei.com>,
Linux Kernel Network Developers <netdev@...r.kernel.org>,
Peter Geis <pgwipeout@...il.com>,
Lu Fengqi <lufq.fnst@...fujitsu.com>,
Daniël Sonck <dsonck92@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
Tejun Heo <tj@...nel.org>
Subject: Re: [Patch net] cgroup: fix cgroup_sk_alloc() for sk_clone_lock()
On Fri, Jun 26, 2020 at 10:58:14AM -0700, Cong Wang wrote:
> On Thu, Jun 25, 2020 at 10:23 PM Cameron Berkenpas <cam@...-zeon.de> wrote:
> >
> > Hello,
> >
> > Somewhere along the way I got the impression that it generally takes
> > those affected hours before their systems lock up. I'm (generally) able
> > to reproduce this issue much faster than that. Regardless, I can help test.
> >
> > Are there any patches that need testing or is this all still pending
> > discussion around the best way to resolve the issue?
>
> Yes. I come up with a (hopefully) much better patch in the attachment.
> Can you help to test it? You need to unapply the previous patch before
> applying this one.
>
> (Just in case of any confusion: I still believe we should check NULL on
> top of this refcnt fix. But it should be a separate patch.)
>
> Thank you!
Not opposing the patch, but the Fixes tag is still confusing me.
Do we have an explanation for what's wrong with 4bfc0bb2c60e?
It looks like we have cgroup_bpf_get()/put() exactly where we have
cgroup_get()/put(), so it would be nice to understand what's different
if the problem is bpf-related.
Thanks!
> commit 259150604c0b77c717fdaab057da5722e2dfd922
> Author: Cong Wang <xiyou.wangcong@...il.com>
> Date: Sat Jun 13 12:34:40 2020 -0700
>
> cgroup: fix cgroup_sk_alloc() for sk_clone_lock()
>
> When we clone a socket in sk_clone_lock(), its sk_cgrp_data is
> copied, so the cgroup refcnt must be taken too. And, unlike the
> sk_alloc() path, sock_update_netprioidx() is not called here.
> Therefore, it is safe and necessary to grab the cgroup refcnt
> even when cgroup_sk_alloc is disabled.
>
> sk_clone_lock() is in BH context anyway, the in_interrupt()
> would terminate this function if called there. And for sk_alloc()
> skcd->val is always zero. So it's safe to factor out the code
> to make it more readable.
>
> Fixes: 4bfc0bb2c60e ("bpf: decouple the lifetime of cgroup_bpf from cgroup itself")
> Reported-by: Cameron Berkenpas <cam@...-zeon.de>
> Reported-by: Peter Geis <pgwipeout@...il.com>
> Reported-by: Lu Fengqi <lufq.fnst@...fujitsu.com>
> Reported-by: Daniël Sonck <dsonck92@...il.com>
> Tested-by: Cameron Berkenpas <cam@...-zeon.de>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Zefan Li <lizefan@...wei.com>
> Cc: Tejun Heo <tj@...nel.org>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
>
> diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
> index 52661155f85f..4f1cd0edc57d 100644
> --- a/include/linux/cgroup-defs.h
> +++ b/include/linux/cgroup-defs.h
> @@ -790,7 +790,8 @@ struct sock_cgroup_data {
> union {
> #ifdef __LITTLE_ENDIAN
> struct {
> - u8 is_data;
> + u8 is_data : 1;
> + u8 no_refcnt : 1;
> u8 padding;
> u16 prioidx;
> u32 classid;
> @@ -800,7 +801,8 @@ struct sock_cgroup_data {
> u32 classid;
> u16 prioidx;
> u8 padding;
> - u8 is_data;
> + u8 no_refcnt : 1;
> + u8 is_data : 1;
> } __packed;
> #endif
> u64 val;
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 4598e4da6b1b..618838c48313 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -822,6 +822,7 @@ extern spinlock_t cgroup_sk_update_lock;
>
> void cgroup_sk_alloc_disable(void);
> void cgroup_sk_alloc(struct sock_cgroup_data *skcd);
> +void cgroup_sk_clone(struct sock_cgroup_data *skcd);
> void cgroup_sk_free(struct sock_cgroup_data *skcd);
>
> static inline struct cgroup *sock_cgroup_ptr(struct sock_cgroup_data *skcd)
> @@ -835,7 +836,7 @@ static inline struct cgroup *sock_cgroup_ptr(struct sock_cgroup_data *skcd)
> */
> v = READ_ONCE(skcd->val);
>
> - if (v & 1)
> + if (v & 3)
> return &cgrp_dfl_root.cgrp;
>
> return (struct cgroup *)(unsigned long)v ?: &cgrp_dfl_root.cgrp;
> @@ -847,6 +848,7 @@ static inline struct cgroup *sock_cgroup_ptr(struct sock_cgroup_data *skcd)
> #else /* CONFIG_CGROUP_DATA */
>
> static inline void cgroup_sk_alloc(struct sock_cgroup_data *skcd) {}
> +static inline void cgroup_sk_clone(struct sock_cgroup_data *skcd) {}
> static inline void cgroup_sk_free(struct sock_cgroup_data *skcd) {}
>
> #endif /* CONFIG_CGROUP_DATA */
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 1ea181a58465..dd247747ec14 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -6439,18 +6439,8 @@ void cgroup_sk_alloc_disable(void)
>
> void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
> {
> - if (cgroup_sk_alloc_disabled)
> - return;
> -
> - /* Socket clone path */
> - if (skcd->val) {
> - /*
> - * We might be cloning a socket which is left in an empty
> - * cgroup and the cgroup might have already been rmdir'd.
> - * Don't use cgroup_get_live().
> - */
> - cgroup_get(sock_cgroup_ptr(skcd));
> - cgroup_bpf_get(sock_cgroup_ptr(skcd));
> + if (cgroup_sk_alloc_disabled) {
> + skcd->no_refcnt = 1;
> return;
> }
>
> @@ -6475,10 +6465,27 @@ void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
> rcu_read_unlock();
> }
>
> +void cgroup_sk_clone(struct sock_cgroup_data *skcd)
> +{
> + if (skcd->val) {
> + if (skcd->no_refcnt)
> + return;
> + /*
> + * We might be cloning a socket which is left in an empty
> + * cgroup and the cgroup might have already been rmdir'd.
> + * Don't use cgroup_get_live().
> + */
> + cgroup_get(sock_cgroup_ptr(skcd));
> + cgroup_bpf_get(sock_cgroup_ptr(skcd));
> + }
> +}
> +
> void cgroup_sk_free(struct sock_cgroup_data *skcd)
> {
> struct cgroup *cgrp = sock_cgroup_ptr(skcd);
>
> + if (skcd->no_refcnt)
> + return;
> cgroup_bpf_put(cgrp);
> cgroup_put(cgrp);
> }
> diff --git a/net/core/sock.c b/net/core/sock.c
> index d832c650287c..2e5b7870e5d3 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1926,7 +1926,7 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> /* sk->sk_memcg will be populated at accept() time */
> newsk->sk_memcg = NULL;
>
> - cgroup_sk_alloc(&newsk->sk_cgrp_data);
> + cgroup_sk_clone(&newsk->sk_cgrp_data);
>
> rcu_read_lock();
> filter = rcu_dereference(sk->sk_filter);
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