From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Song Liu <songliubraving@fb.com>
Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, ast@kernel.org,
daniel@iogearbox.net, andrii@kernel.org,
john.fastabend@gmail.com, kpsingh@chromium.org,
kernel-team@fb.com
Subject: Re: [PATCH v2 bpf-next 1/4] bpf: introduce task_vma bpf_iter
Date: Thu, 17 Dec 2020 11:03:08 -0800 [thread overview]
Message-ID: <20201217190308.insbsxpf6ujapbs3@ast-mbp> (raw)
In-Reply-To: <20201215233702.3301881-2-songliubraving@fb.com>
On Tue, Dec 15, 2020 at 03:36:59PM -0800, Song Liu wrote:
> +/*
> + * Key information from vm_area_struct. We need this because we cannot
> + * assume the vm_area_struct is still valid after each iteration.
> + */
> +struct __vm_area_struct {
> + __u64 start;
> + __u64 end;
> + __u64 flags;
> + __u64 pgoff;
> +};
Where it's inside .c or exposed in uapi/bpf.h it will become uapi
if it's used this way. Let's switch to arbitrary BTF-based access instead.
> +static struct __vm_area_struct *
> +task_vma_seq_get_next(struct bpf_iter_seq_task_vma_info *info)
> +{
> + struct pid_namespace *ns = info->common.ns;
> + struct task_struct *curr_task;
> + struct vm_area_struct *vma;
> + u32 curr_tid = info->tid;
> + bool new_task = false;
> +
> + /* If this function returns a non-NULL __vm_area_struct, it held
> + * a reference to the task_struct. If info->file is non-NULL, it
> + * also holds a reference to the file. If this function returns
> + * NULL, it does not hold any reference.
> + */
> +again:
> + if (info->task) {
> + curr_task = info->task;
> + } else {
> + curr_task = task_seq_get_next(ns, &curr_tid, true);
> + if (!curr_task) {
> + info->task = NULL;
> + info->tid++;
> + return NULL;
> + }
> +
> + if (curr_tid != info->tid) {
> + info->tid = curr_tid;
> + new_task = true;
> + }
> +
> + if (!curr_task->mm)
> + goto next_task;
> + info->task = curr_task;
> + }
> +
> + mmap_read_lock(curr_task->mm);
That will hurt. /proc readers do that and it causes all sorts
of production issues. We cannot take this lock.
There is no need to take it.
Switch the whole thing to probe_read style walking.
And reimplement find_vma with probe_read while omitting vmacache.
It will be short rbtree walk.
bpf prog doesn't need to see a stable struct. It will read it through ptr_to_btf_id
which will use probe_read equivalent underneath.
next prev parent reply other threads:[~2020-12-17 19:04 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-15 23:36 [PATCH v2 bpf-next 0/4] introduce bpf_iter for task_vma Song Liu
2020-12-15 23:36 ` [PATCH v2 bpf-next 1/4] bpf: introduce task_vma bpf_iter Song Liu
2020-12-16 17:36 ` Yonghong Song
2020-12-16 19:41 ` Song Liu
2020-12-17 0:34 ` Andrii Nakryiko
2020-12-17 1:51 ` Song Liu
2020-12-17 19:03 ` Alexei Starovoitov [this message]
2020-12-17 22:08 ` Song Liu
2020-12-18 2:34 ` Alexei Starovoitov
2020-12-18 3:15 ` Yonghong Song
2020-12-18 4:33 ` Song Liu
2020-12-18 5:23 ` Alexei Starovoitov
2020-12-18 16:38 ` Yonghong Song
2020-12-18 17:23 ` Song Liu
2021-01-05 1:46 ` Alexei Starovoitov
2021-01-05 5:47 ` Song Liu
2021-01-05 16:27 ` Alexei Starovoitov
2021-01-05 17:10 ` Song Liu
2021-01-05 17:27 ` Alexei Starovoitov
2021-01-05 19:38 ` Song Liu
2021-01-05 19:46 ` Alexei Starovoitov
2021-01-05 19:51 ` Song Liu
2020-12-15 23:37 ` [PATCH v2 bpf-next 2/4] bpf: allow bpf_d_path in sleepable bpf_iter program Song Liu
2020-12-16 17:41 ` Yonghong Song
2020-12-16 18:15 ` KP Singh
2020-12-16 18:31 ` KP Singh
2021-01-25 12:52 ` Jiri Olsa
2020-12-15 23:37 ` [PATCH v2 bpf-next 3/4] libbpf: introduce section "iter.s/" for " Song Liu
2020-12-16 17:42 ` Yonghong Song
2020-12-16 18:00 ` KP Singh
2020-12-15 23:37 ` [PATCH v2 bpf-next 4/4] selftests/bpf: add test for bpf_iter_task_vma Song Liu
2020-12-16 18:18 ` Yonghong Song
2020-12-16 23:23 ` Song Liu
2020-12-16 17:00 ` [PATCH v2 bpf-next 0/4] introduce bpf_iter for task_vma Yonghong Song
2020-12-16 17:35 ` Song Liu
2020-12-16 18:31 ` Yonghong Song
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