From: Yonghong Song <yhs@fb.com>
To: Alan Maguire <alan.maguire@oracle.com>
Cc: <ast@kernel.org>, <daniel@iogearbox.net>, <bpf@vger.kernel.org>,
<joe@perches.com>, <linux@rasmusvillemoes.dk>,
<arnaldo.melo@gmail.com>, <kafai@fb.com>, <songliubraving@fb.com>,
<andriin@fb.com>, <john.fastabend@gmail.com>,
<kpsingh@chromium.org>, <linux-kernel@vger.kernel.org>,
<netdev@vger.kernel.org>
Subject: Re: [PATCH v2 bpf-next 6/7] bpf: add support for %pT format specifier for bpf_trace_printk() helper
Date: Mon, 18 May 2020 07:47:56 -0700 [thread overview]
Message-ID: <91960eea-fb43-c26d-f8bb-256d37d5903f@fb.com> (raw)
In-Reply-To: <alpine.LRH.2.21.2005181000520.893@localhost>
On 5/18/20 2:10 AM, Alan Maguire wrote:
> On Wed, 13 May 2020, Yonghong Song wrote:
>
>>
>>> + while (isbtffmt(fmt[i]))
>>> + i++;
>>
>> The pointer passed to the helper may not be valid pointer. I think you
>> need to do a probe_read_kernel() here. Do an atomic memory allocation
>> here should be okay as this is mostly for debugging only.
>>
>
> Are there other examples of doing allocations in program execution
> context? I'd hate to be the first to introduce one if not. I was hoping
> I could get away with some per-CPU scratch space. Most data structures
> will fit within a small per-CPU buffer, but if multiple copies
> are required, performance isn't the key concern. It will make traversing
> the buffer during display a bit more complex but I think avoiding
> allocation might make that complexity worth it. The other thought I had
> was we could carry out an allocation associated with the attach,
> but that's messy as it's possible run-time might determine the type for
> display (and thus the amount of the buffer we need to copy safely).
percpu buffer definitely better. In fact, I am using percpu buffer
in bpf_seq_printf() helper. Yes, you will need to handling contention
though. I guess we can do the same thing here, return -EBUSY so bpf
program can react properly (retry, or just print error, etc.)
if there is a contention.
>
> Great news about LLVM support for __builtin_btf_type_id()!
Thanks. Hopefully this will make implementation easier.
>
> Thanks!
>
> Alan
>
next prev parent reply other threads:[~2020-05-18 14:48 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-12 5:56 [PATCH v2 bpf-next 0/7] bpf, printk: add BTF-based type printing Alan Maguire
2020-05-12 5:56 ` [PATCH v2 bpf-next 1/7] bpf: provide function to get vmlinux BTF information Alan Maguire
2020-05-12 5:56 ` [PATCH v2 bpf-next 2/7] bpf: move to generic BTF show support, apply it to seq files/strings Alan Maguire
2020-05-13 23:04 ` Yonghong Song
2020-05-18 9:46 ` Alan Maguire
2020-05-19 6:21 ` Yonghong Song
2020-05-12 5:56 ` [PATCH v2 bpf-next 3/7] checkpatch: add new BTF pointer format specifier Alan Maguire
2020-05-12 5:56 ` [PATCH v2 bpf-next 4/7] printk: add type-printing %pT format specifier which uses BTF Alan Maguire
2020-05-13 23:05 ` Joe Perches
2020-05-13 23:07 ` Alexei Starovoitov
2020-05-13 23:22 ` Joe Perches
2020-05-14 23:43 ` Joe Perches
2020-05-15 0:09 ` Alexei Starovoitov
2020-05-15 0:21 ` Joe Perches
2020-05-14 0:45 ` Yonghong Song
2020-05-14 22:37 ` Alan Maguire
2020-05-15 0:39 ` Yonghong Song
2020-05-12 5:56 ` [PATCH v2 bpf-next 5/7] printk: extend test_printf to test %pT BTF-based format specifier Alan Maguire
2020-05-12 5:56 ` [PATCH v2 bpf-next 6/7] bpf: add support for %pT format specifier for bpf_trace_printk() helper Alan Maguire
2020-05-14 0:53 ` Yonghong Song
2020-05-18 9:10 ` Alan Maguire
2020-05-18 14:47 ` Yonghong Song [this message]
2020-05-12 5:56 ` [PATCH v2 bpf-next 7/7] bpf: add tests for %pT format specifier Alan Maguire
2020-05-15 0:21 ` Andrii Nakryiko
2020-05-13 22:24 ` [PATCH v2 bpf-next 0/7] bpf, printk: add BTF-based type printing Alexei Starovoitov
2020-05-13 22:48 ` Joe Perches
2020-05-13 22:50 ` Alexei Starovoitov
2020-05-13 23:23 ` Joe Perches
2020-05-14 17:46 ` Alan Maguire
2020-05-15 18:59 ` Yonghong Song
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=91960eea-fb43-c26d-f8bb-256d37d5903f@fb.com \
--to=yhs@fb.com \
--cc=alan.maguire@oracle.com \
--cc=andriin@fb.com \
--cc=arnaldo.melo@gmail.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=joe@perches.com \
--cc=john.fastabend@gmail.com \
--cc=kafai@fb.com \
--cc=kpsingh@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@rasmusvillemoes.dk \
--cc=netdev@vger.kernel.org \
--cc=songliubraving@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox