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SubjectRe: [PATCH 4.19 03/89] cgroup, netclassid: periodically release file_lock on classid updating
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On 18/03/2020 12.02, Pavel Machek wrote:
> Hi!
>
>> From: Dmitry Yakunin <zeil@yandex-team.ru>
>>
>> [ Upstream commit 018d26fcd12a75fb9b5fe233762aa3f2f0854b88 ]
> ...
>> Now update is non atomic and socket may be skipped using calls:
>>
>> dup2(oldfd, newfd);
>> close(oldfd);
>>
>> But this case is not typical. Moreover before this patch skip is possible
>> too by hiding socket fd in unix socket buffer.
>
> Dunno. This makes interface even more interesting.

This is part of brilliant cgroup-v1 design. =)
Cgroup-v2 doesn't recolor sockets when task is moved.

>
>> +
>> static int update_classid_sock(const void *v, struct file *file, unsigned n)
>> {
>> int err;
>> + struct update_classid_context *ctx = (void *)v;
>> struct socket *sock = sock_from_file(file, &err);
>>
> ...
>> + if (--ctx->batch == 0) {
>> + ctx->batch = UPDATE_CLASSID_BATCH;
>> + return n + 1;
>> + }
>> return 0;
>> }
>
> We take "const void *" and then write to it. That's asking for
> trouble... right? Should the const annotation be removed, at least for
> sake of humans trying to understand the code?

Indeed, there is no much sense in opaque const void *.
This is how iterate_fd() is declared.

>
> Best regards,
> Pavel
>

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