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Subject: Re: [PATCH v6 3/7] Reimplement RLIMIT_NPROC on top of ucounts
To:     Alexey Gladkov <gladkov.alexey@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, io-uring@vger.kernel.org,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Linux Containers <containers@lists.linux-foundation.org>,
        linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>
References: <cover.1613392826.git.gladkov.alexey@gmail.com>
 <72fdcd154bec7e0dfad090f1af65ddac1e767451.1613392826.git.gladkov.alexey@gmail.com>
 <72214339-57fc-e47f-bb57-d1b39c69e38e@kernel.dk>
 <20210222101141.uve6hnftsakf4u7n@example.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <73b37a89-79d2-9c04-0626-2b164e91c3a8@kernel.dk>
Date:   Mon, 22 Feb 2021 07:09:41 -0700
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On 2/22/21 3:11 AM, Alexey Gladkov wrote:
> On Sun, Feb 21, 2021 at 04:38:10PM -0700, Jens Axboe wrote:
>> On 2/15/21 5:41 AM, Alexey Gladkov wrote:
>>> diff --git a/fs/io-wq.c b/fs/io-wq.c
>>> index a564f36e260c..5b6940c90c61 100644
>>> --- a/fs/io-wq.c
>>> +++ b/fs/io-wq.c
>>> @@ -1090,10 +1091,7 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
>>>  		wqe->node = alloc_node;
>>>  		wqe->acct[IO_WQ_ACCT_BOUND].max_workers = bounded;
>>>  		atomic_set(&wqe->acct[IO_WQ_ACCT_BOUND].nr_running, 0);
>>> -		if (wq->user) {
>>> -			wqe->acct[IO_WQ_ACCT_UNBOUND].max_workers =
>>> -					task_rlimit(current, RLIMIT_NPROC);
>>> -		}
>>> +		wqe->acct[IO_WQ_ACCT_UNBOUND].max_workers = task_rlimit(current, RLIMIT_NPROC);
>>
>> This doesn't look like an equivalent transformation. But that may be
>> moot if we merge the io_uring-worker.v3 series, as then you would not
>> have to touch io-wq at all.
> 
> In the current code the wq->user is always set to current_user():
> 
> io_uring_create [1]
> `- io_sq_offload_create
>    `- io_init_wq_offload [2]
>       `-io_wq_create [3]

current vs other wasn't my concern, but we're always setting ->user so
the test was pointless. So looks fine to me.

-- 
Jens Axboe