perf: Live mode flamegraph recording results in segmentation fault

perf: Live mode flamegraph recording results in segmentation fault

[David]

I've reproduced this on recent versions of Debian, Ubuntu, CentOS, and 
Fedora,
and I used to be able to downgrade perf and it would work, but an early 
enough
version of perf is no longer available from most package repositories.

Steps I have taken to reproduce:

1. Install perf from a distro package manager. ( `sudo dnf install perf`)

```
  $ perf --version

perf version 6.13.5-200.fc41.x86_64)
```

2. Attempt a live flamegraph report:

```

$ perf script flamegraph ls
/usr/libexec/perf-core/scripts/python/bin/flamegraph-report: line 3:  
1644 Segmentation fault      (core dumped) perf script -s 
"$PERF_EXEC_PATH"/scripts/python/flamegraph.py -- "$@"
```

Re: perf: Live mode flamegraph recording results in segmentation fault

[James Clark]

On 07/03/2025 4:25 pm, David wrote:
> I've reproduced this on recent versions of Debian, Ubuntu, CentOS, and 
> Fedora,
> and I used to be able to downgrade perf and it would work, but an early 
> enough
> version of perf is no longer available from most package repositories.
> 
> Steps I have taken to reproduce:
> 
> 1. Install perf from a distro package manager. ( `sudo dnf install perf`)
> 
> ```
>   $ perf --version
> 
> perf version 6.13.5-200.fc41.x86_64)
> ```
> 
> 2. Attempt a live flamegraph report:
> 
> ```
> 
> $ perf script flamegraph ls
> /usr/libexec/perf-core/scripts/python/bin/flamegraph-report: line 3: 
> 1644 Segmentation fault      (core dumped) perf script -s 
> "$PERF_EXEC_PATH"/scripts/python/flamegraph.py -- "$@"
> ```
> 
> 

Hi David,

Are you able to bisect this to find the breaking commit?

Is this the full output you get? I'm not able to reproduce your exact 
issue. I do see a bug with the template download prompt but it produces 
more output than you have:

  $ perf script flamegraph ls

   Warning: Flame Graph template '/usr/share/d3-flame-graph/d3-
   flamegraph-base.html' does not exist.
   [...]
   s = input("Do you wish to download a template from cdn.jsdelivr.net?
   (this warning can be suppressed with --allow-download) [yn] ").lower()
   OSError: [Errno 9] Bad file descriptor
   Fatal Python error: handler_call_die: problem in Python trace event
   handler
   Python runtime state: initialized

   Current thread 0x00007d1916afd400 (most recent call first):
   <no Python frame>

   Extension modules: apt_pkg (total: 1)
   Aborted (core dumped)

But if I avoid the record/report wrapper and go straight to the script 
it works:

   $ perf record -g ls
   $ perf script flamegraph.py

   [...]
   Do you wish to download a template from cdn.jsdelivr.net? (this
   warning can be suppressed with --allow-download) [yn] y

   dumping data to flamegraph.html

I'm wondering if the template prompt ever worked in conjunction with the 
wrappers? Maybe they were only tested with the template already 
installed, or the script was always used directly when the need for a 
template was added.

Thanks
James

Re: perf: Live mode flamegraph recording results in segmentation fault

[Namhyung Kim]

On Mon, Mar 10, 2025 at 11:53:06AM +0000, James Clark wrote:
> 
> 
> On 07/03/2025 4:25 pm, David wrote:
> > I've reproduced this on recent versions of Debian, Ubuntu, CentOS, and
> > Fedora,
> > and I used to be able to downgrade perf and it would work, but an early
> > enough
> > version of perf is no longer available from most package repositories.
> > 
> > Steps I have taken to reproduce:
> > 
> > 1. Install perf from a distro package manager. ( `sudo dnf install perf`)
> > 
> > ```
> >   $ perf --version
> > 
> > perf version 6.13.5-200.fc41.x86_64)
> > ```
> > 
> > 2. Attempt a live flamegraph report:
> > 
> > ```
> > 
> > $ perf script flamegraph ls
> > /usr/libexec/perf-core/scripts/python/bin/flamegraph-report: line 3:
> > 1644 Segmentation fault      (core dumped) perf script -s
> > "$PERF_EXEC_PATH"/scripts/python/flamegraph.py -- "$@"
> > ```
> > 
> > 
> 
> Hi David,
> 
> Are you able to bisect this to find the breaking commit?
> 
> Is this the full output you get? I'm not able to reproduce your exact issue.
> I do see a bug with the template download prompt but it produces more output
> than you have:
> 
>  $ perf script flamegraph ls
> 
>   Warning: Flame Graph template '/usr/share/d3-flame-graph/d3-
>   flamegraph-base.html' does not exist.
>   [...]
>   s = input("Do you wish to download a template from cdn.jsdelivr.net?
>   (this warning can be suppressed with --allow-download) [yn] ").lower()
>   OSError: [Errno 9] Bad file descriptor
>   Fatal Python error: handler_call_die: problem in Python trace event
>   handler
>   Python runtime state: initialized
> 
>   Current thread 0x00007d1916afd400 (most recent call first):
>   <no Python frame>
> 
>   Extension modules: apt_pkg (total: 1)
>   Aborted (core dumped)
> 
> But if I avoid the record/report wrapper and go straight to the script it
> works:
> 
>   $ perf record -g ls
>   $ perf script flamegraph.py
> 
>   [...]
>   Do you wish to download a template from cdn.jsdelivr.net? (this
>   warning can be suppressed with --allow-download) [yn] y
> 
>   dumping data to flamegraph.html
> 
> I'm wondering if the template prompt ever worked in conjunction with the
> wrappers? Maybe they were only tested with the template already installed,
> or the script was always used directly when the need for a template was
> added.

I don't know but it didn't work well for me too.  Maybe it should have
default 'y' for live mode.

Thanks,
Namhyung

Re: perf: Live mode flamegraph recording results in segmentation fault

[James Clark]

On 10/03/2025 9:30 pm, Namhyung Kim wrote:
> On Mon, Mar 10, 2025 at 11:53:06AM +0000, James Clark wrote:
>>
>>
>> On 07/03/2025 4:25 pm, David wrote:
>>> I've reproduced this on recent versions of Debian, Ubuntu, CentOS, and
>>> Fedora,
>>> and I used to be able to downgrade perf and it would work, but an early
>>> enough
>>> version of perf is no longer available from most package repositories.
>>>
>>> Steps I have taken to reproduce:
>>>
>>> 1. Install perf from a distro package manager. ( `sudo dnf install perf`)
>>>
>>> ```
>>>    $ perf --version
>>>
>>> perf version 6.13.5-200.fc41.x86_64)
>>> ```
>>>
>>> 2. Attempt a live flamegraph report:
>>>
>>> ```
>>>
>>> $ perf script flamegraph ls
>>> /usr/libexec/perf-core/scripts/python/bin/flamegraph-report: line 3:
>>> 1644 Segmentation fault      (core dumped) perf script -s
>>> "$PERF_EXEC_PATH"/scripts/python/flamegraph.py -- "$@"
>>> ```
>>>
>>>
>>
>> Hi David,
>>
>> Are you able to bisect this to find the breaking commit?
>>
>> Is this the full output you get? I'm not able to reproduce your exact issue.
>> I do see a bug with the template download prompt but it produces more output
>> than you have:
>>
>>   $ perf script flamegraph ls
>>
>>    Warning: Flame Graph template '/usr/share/d3-flame-graph/d3-
>>    flamegraph-base.html' does not exist.
>>    [...]
>>    s = input("Do you wish to download a template from cdn.jsdelivr.net?
>>    (this warning can be suppressed with --allow-download) [yn] ").lower()
>>    OSError: [Errno 9] Bad file descriptor
>>    Fatal Python error: handler_call_die: problem in Python trace event
>>    handler
>>    Python runtime state: initialized
>>
>>    Current thread 0x00007d1916afd400 (most recent call first):
>>    <no Python frame>
>>
>>    Extension modules: apt_pkg (total: 1)
>>    Aborted (core dumped)
>>
>> But if I avoid the record/report wrapper and go straight to the script it
>> works:
>>
>>    $ perf record -g ls
>>    $ perf script flamegraph.py
>>
>>    [...]
>>    Do you wish to download a template from cdn.jsdelivr.net? (this
>>    warning can be suppressed with --allow-download) [yn] y
>>
>>    dumping data to flamegraph.html
>>
>> I'm wondering if the template prompt ever worked in conjunction with the
>> wrappers? Maybe they were only tested with the template already installed,
>> or the script was always used directly when the need for a template was
>> added.
> 
> I don't know but it didn't work well for me too.  Maybe it should have
> default 'y' for live mode.
> 
> Thanks,
> Namhyung
> 

Looks like this bug was discussed previously here [2].

And the issue about shipping vs downloading here along with prompting on 
the original change [1]. But considering the following I think it's 
worth bringing it up again:

  * We download a fixed version (rather than latest)
  * The contents are hash checked so are fixed for that reason too
  * We know network requests should be avoided (so prompt for input)
  * The packaging request didn't go anywhere

In light of all of the above what's the difference between downloading 
it vs packaging it into Perf? It has an Apache licence, but I'm pretty 
sure it's separate enough for that to not be an issue.

One argument was that it's a minimized blob, but only the .min.js is. 
The unminimized version is available too.

[1]: 
https://lore.kernel.org/lkml/928c76bf-39bc-cbc0-373e-70c5561cd5b0@redhat.com/T/#mf0942ae7abc78882c9b10b1c1f18a119393e3e2b

[2]: 
https://lore.kernel.org/all/CAP-5=fW+jpi_iLCrpA2GeEQBzNYASF52qrX7ExrSNL82uaDREQ@mail.gmail.com/