/me bets on a reference counting error.

Hello. Thanks for reply. My script is only plain python, using only bpy, mesh and mathutils (only Vector) modules. No extenal C code. This is the reason why I reported this here.

If you wish, I can share my python script, even if it's not ready for public. My script also needs some interaction, which I can't fully describe, so I don't know if it helps.

Either way, we need a way to reproduce the crash. We can't, and won't, debug through an entire addon to do so. A simplified repro is necessary. Strip out as much as possible until you arrive at only the pieces that are necessary.

Sorry, I can't reproduce this in a small script, however I found a problem. Using this function fails:

def bevel(cover, offset, segments=10):
    bm = bmesh.from_edit_mesh(cover.data)
    bmesh.ops.bevel(bm,
      geom=[x for x in bm.verts[:]+bm.edges[:] if x.select],
      offset=offset,
      offset_type='OFFSET',
      segments=segments,
      profile=0.5,
      affect="EDGES", #vertex_only=False,
      loop_slide=True,
      clamp_overlap=True
    )
    bmesh.update_edit_mesh(cover.data)
    bm.free()

After removal of bm.free(), script works again.
@Stephen Swaney (stiv), thank you for pointing me to an referencing error.

Why this bm.free() exists and should or shouldn't be called? In blender's documentation I found, that I should call it.

I think it's not necessary to call bm.free()
Data is expected to get freed at the end of function execution.

We may handle this as a valid report if that call is responsible for the crash.

I can confirm, that reenable of bm.free() will crash again and after removal it's back.

This script doesn't crash on bm.free() or at end of function, but crashes aprox. 10 rows after return from this function. May be crash log from this report can help to identify, what's happening.

My initial problem has been solved by removing of bm.free(), but I am ready to do more tests if needed. Just let me know, how I can help.

This script doesn't crash on bm.free() or at end of function, but crashes aprox. 10 rows after return from this function. May be crash log from this report can help to identify, > what's happening.

There might be an issue in your script itself (Still I'm not sure unless we have steps to reproduce it).
Please try one of the community websites: https://www.blender.org/community/
If you think you found a bug, please submit a new report and carefully follow the instructions. Be sure to provide system information, Blender version, and a .blend file with exact steps to reproduce the problem.

Just in case I'm missing something, @Philipp Oeser (lichtwerk), can you check?

To speed the process up (there are multiple people looking at this already), please always attach a .blend file where this script is already set up to just be executed from the Text Editor.
(This also ensures we are all on the same page)

There is no .blend file. My script is running from blender addons and is using multiple scripts.

@Ondrej Novak (ondrew) : than please share that here or try to isolate relevant parts into a script (embedded in a .blend file) with clear steps to reproduce

@Philipp Oeser (lichtwerk), you mentioned wrong people. :-)

So ok, I am adding my script. First is: boxmaker.py:

Copy this to addons and enable it.

Download pir.py:

and run:

blender -P pir.py

This crashes my blender. Not tested today.
Removing of "bm.free()" can fix this script.

Please, do not ask me to make this script simpler. I can't figure, where is the exact problem.

@Jan Ondrej (ondrejj) please make a simple test script that causes the error without relying on a separate add-on.

Any logic that isn't related to reproducing the crash should be removed.

Sorry, but I can't. My blender script programming is not good enough to do this. I did some experiment but without any success.

@Jan Ondrej (ondrejj) it should not be so difficult to merge the add-on into a script, then remove function calls - checking the crash still occurs.

But don't know which calls to remove. After removal of one line which makes a problem this problem moves to another line. Sorry, but as I said, I did some experiments, but without success.

@Jan Ondrej (ondrejj) uploaded a slightly simplified script with tracing enabled that runs in background mode and crashes reliably, this needs some more investigation though.

Edit: this seems to be memory corruption however it's not clear where exactly this occurs, tested with ASAN and Valgrind don't point to anything obvious.
It looks like the Python state is corrupted some time before the crash occurs.

Report is already classified as a Bug so can we also mark it as "Confirmed"?