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Message-ID: <1ea32c1c-babf-452d-8097-c23777e8018b@bytedance.com>
Date: Wed, 11 Oct 2023 13:32:02 +0800
From: Chuyi Zhou <zhouchuyi@...edance.com>
To: bpf@...r.kernel.org
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
martin.lau@...nel.org, tj@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 4/8] bpf: Introduce css open-coded iterator
kfuncs
在 2023/10/11 12:44, Chuyi Zhou 写道:
>
>
> 在 2023/10/7 20:45, Chuyi Zhou 写道:
>> This Patch adds kfuncs bpf_iter_css_{new,next,destroy} which allow
>> creation and manipulation of struct bpf_iter_css in open-coded iterator
>> style. These kfuncs actually wrapps css_next_descendant_{pre, post}.
>> css_iter can be used to:
>>
>> 1) iterating a sepcific cgroup tree with pre/post/up order
>>
>> 2) iterating cgroup_subsystem in BPF Prog, like
>> for_each_mem_cgroup_tree/cpuset_for_each_descendant_pre in kernel.
>>
>> The API design is consistent with cgroup_iter. bpf_iter_css_new accepts
>> parameters defining iteration order and starting css. Here we also reuse
>> BPF_CGROUP_ITER_DESCENDANTS_PRE, BPF_CGROUP_ITER_DESCENDANTS_POST,
>> BPF_CGROUP_ITER_ANCESTORS_UP enums.
>>
>> Signed-off-by: Chuyi Zhou <zhouchuyi@...edance.com>
>> Acked-by: Tejun Heo <tj@...nel.org>
>> ---
>> kernel/bpf/cgroup_iter.c | 59 +++++++++++++++++++
>> kernel/bpf/helpers.c | 3 +
>> .../testing/selftests/bpf/bpf_experimental.h | 6 ++
>> 3 files changed, 68 insertions(+)
>>
>> diff --git a/kernel/bpf/cgroup_iter.c b/kernel/bpf/cgroup_iter.c
>> index 810378f04fbc..9c6ad892ae82 100644
>> --- a/kernel/bpf/cgroup_iter.c
>> +++ b/kernel/bpf/cgroup_iter.c
>> @@ -294,3 +294,62 @@ static int __init bpf_cgroup_iter_init(void)
>> }
>> late_initcall(bpf_cgroup_iter_init);
>> +
>> +struct bpf_iter_css {
>> + __u64 __opaque[3];
>> +} __attribute__((aligned(8)));
>> +
>> +struct bpf_iter_css_kern {
>> + struct cgroup_subsys_state *start;
>> + struct cgroup_subsys_state *pos;
>> + unsigned int flags;
>> +} __attribute__((aligned(8)));
>> +
>> +__bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css *it,
>> + struct cgroup_subsys_state *start, unsigned int flags)
>> +{
>> + struct bpf_iter_css_kern *kit = (void *)it;
>> +
>> + BUILD_BUG_ON(sizeof(struct bpf_iter_css_kern) != sizeof(struct
>> bpf_iter_css));
>> + BUILD_BUG_ON(__alignof__(struct bpf_iter_css_kern) !=
>> __alignof__(struct bpf_iter_css));
>> +
>
> This would cause the fail of netdev/build_32bit CI
> (https://netdev.bots.linux.dev/static/nipa/790929/13412333/build_32bit/stderr):
>
> tools/testing/selftests/kvm/settings: warning: ignored by one of the
> .gitignore files
> ../kernel/bpf/cgroup_iter.c:308:17: warning: no previous prototype for
> ‘bpf_iter_css_new’ [-Wmissing-prototypes]
> 308 | __bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css *it,
> | ^~~~~~~~~~~~~~~~
> ../kernel/bpf/cgroup_iter.c:332:41: warning: no previous prototype for
> ‘bpf_iter_css_next’ [-Wmissing-prototypes]
> 332 | __bpf_kfunc struct cgroup_subsys_state
> *bpf_iter_css_next(struct bpf_iter_css *it)
> | ^~~~~~~~~~~~~~~~~
> ../kernel/bpf/cgroup_iter.c:353:18: warning: no previous prototype for
> ‘bpf_iter_css_destroy’ [-Wmissing-prototypes]
> 353 | __bpf_kfunc void bpf_iter_css_destroy(struct bpf_iter_css *it)
> | ^~~~~~~~~~~~~~~~~~~~
> In file included from <command-line>:
> ../kernel/bpf/cgroup_iter.c: In function ‘bpf_iter_css_new’:
> ./../include/linux/compiler_types.h:425:45: error: call to
> ‘__compiletime_assert_322’ declared with attribute error: BUILD_BUG_ON
> failed: sizeof(struct bpf_iter_css_kern) != sizeof(struct bpf_iter_css)
> 425 | _compiletime_assert(condition, msg,
> __compiletime_assert_, __COUNTER__)
> | ^
> ./../include/linux/compiler_types.h:406:25: note: in definition of macro
> ‘__compiletime_assert’
> 406 | prefix ## suffix(); \
> | ^~~~~~
> ./../include/linux/compiler_types.h:425:9: note: in expansion of macro
> ‘_compiletime_assert’
> 425 | _compiletime_assert(condition, msg,
> __compiletime_assert_, __COUNTER__)
> | ^~~~~~~~~~~~~~~~~~~
> ../include/linux/build_bug.h:39:37: note: in expansion of macro
> ‘compiletime_assert’
> 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond),
> msg)
> | ^~~~~~~~~~~~~~~~~~
> ../include/linux/build_bug.h:50:9: note: in expansion of macro
> ‘BUILD_BUG_ON_MSG’
> 50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: "
> #condition)
> | ^~~~~~~~~~~~~~~~
> ../kernel/bpf/cgroup_iter.c:313:9: note: in expansion of macro
> ‘BUILD_BUG_ON’
> 313 | BUILD_BUG_ON(sizeof(struct bpf_iter_css_kern) !=
> sizeof(struct bpf_iter_css));
>
>
> The reason seems on 32-bit machine, sizeof(struct bpf_iter_css) is 24
> and sizeof(struct bpf_iter_css_kern) is 16.
>
> I was wondering whether the BUILD_BUG_ON check is necessary. Looking at
> the struct bpf_list_node and struct bpf_list_node_kern wich are very
> similay to bpf_iter_css, I didn't see the BUILD_BUG_ON check when
> convert from (struct bpf_list_node *) to (struct bpf_list_node_kern *)
>
> /* Non-opaque version of bpf_list_node in uapi/linux/bpf.h */
> struct bpf_list_node_kern {
> struct list_head list_head;
> void *owner;
> } __attribute__((aligned(8)));
>
> struct bpf_list_node {
> __u64 :64;
> __u64 :64;
> __u64 :64;
> } __attribute__((aligned(8)));
>
> __bpf_kfunc int bpf_list_push_back_impl(struct bpf_list_head *head,
> struct bpf_list_node *node,
> void *meta__ign, u64 off)
> {
> struct bpf_list_node_kern *n = (void *)node;
>
> }
>
or we can change the BUILD_BUG_ON check, like bpf_timer_kern in
bpf_timer_init:
--- a/kernel/bpf/cgroup_iter.c
+++ b/kernel/bpf/cgroup_iter.c
@@ -310,7 +310,7 @@ __bpf_kfunc int bpf_iter_css_new(struct bpf_iter_css
*it,
{
struct bpf_iter_css_kern *kit = (void *)it;
- BUILD_BUG_ON(sizeof(struct bpf_iter_css_kern) != sizeof(struct
bpf_iter_css));
+ BUILD_BUG_ON(sizeof(struct bpf_iter_css_kern) > sizeof(struct
bpf_iter_css));
BUILD_BUG_ON(__alignof__(struct bpf_iter_css_kern) !=
__alignof__(struct bpf_iter_css));
kit->start = NULL;
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 773be9a221f5..0772545568f1 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -877,7 +877,7 @@ __bpf_kfunc int bpf_iter_task_new(struct
bpf_iter_task *it,
{
struct bpf_iter_task_kern *kit = (void *)it;
- BUILD_BUG_ON(sizeof(struct bpf_iter_task_kern) != sizeof(struct
bpf_iter_task));
+ BUILD_BUG_ON(sizeof(struct bpf_iter_task_kern) > sizeof(struct
bpf_iter_task));
BUILD_BUG_ON(__alignof__(struct bpf_iter_task_kern) !=
__alignof__(struct bpf_iter_task));
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