netdev - Re: [PATCH bpf v2 0/3] bpf: two fixes for bpf iterators

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Date:   Tue, 18 Aug 2020 15:28:25 -0700
From:   Yonghong Song <yhs@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>
Subject: Re: [PATCH bpf v2 0/3] bpf: two fixes for bpf iterators



On 8/18/20 3:23 PM, Yonghong Song wrote:
> Patch #1 fixed a rcu stall warning when traversing large number
> of tasks/files without overflowing seq_file buffer. The method
> is to control the number of visited objects in bpf_seq_read()
> so all bpf iterators will benefit.
> 
> Patch #2 calculated tid properly in a namespace in order to avoid
> visiting the name task multiple times.
> 
> Patch #3 handled read() error code EAGAIN properly in bpftool
> bpf_iter userspace code to collect pids. The change is needed
> due to Patch #1.

Sorry. Missed the changelog below.

Changelogs:
   - v1 -> v2:
     . do ratelimiting in bpf_seq_read() with a counter.
       cond_resched() doesn't work as some iterators (e.g., tcp,
       netlink, etc.) has rcu read critical section across
       consecutive seq_ops->next() functions.

> 
> Yonghong Song (3):
>    bpf: fix a rcu_sched stall issue with bpf task/task_file iterator
>    bpf: avoid visit same object multiple times
>    bpftool: handle EAGAIN error code properly in pids collection
> 
>   kernel/bpf/bpf_iter.c    | 15 ++++++++++++++-
>   kernel/bpf/task_iter.c   |  3 ++-
>   tools/bpf/bpftool/pids.c |  2 ++
>   3 files changed, 18 insertions(+), 2 deletions(-)
>