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occasional null pointer dereference in slp_kill_tasks_with_stacks #105

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ghost opened this issue Nov 29, 2016 · 3 comments
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occasional null pointer dereference in slp_kill_tasks_with_stacks #105

ghost opened this issue Nov 29, 2016 · 3 comments
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2.7-slp bug major stackless python
Milestone
2.7.13-slp

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@ghost
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ghost commented Nov 29, 2016 •
edited by ghost
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Originally reported by: Johnny Healey (Bitbucket: johealey, GitHub: revnull)

I've been encountering segfaults while shutting down stackless. Debugging with gdb lead to a for loop that doesn't seem to be checking to see if the value it is iterating over is null.

I've attached a proposed patch.
null_ptr.patch.zip
test_issue105.py.zip
@ghost
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ghost commented Dec 2, 2016

Original comment by Anselm Kruis (Bitbucket: akruis, GitHub: akruis):

Hi Johnny,

many thanks for the report. Do you have a python script, that reproduces the bug?

Kind regards
Anselm

@ghost
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ghost commented Dec 4, 2016

Original comment by Anselm Kruis (Bitbucket: akruis, GitHub: akruis):

I was able to craft a test case, that triggers the bug reliable.
The for(cs = csfirst; !(in_loop && cs == csfirst); cs = cs->next) loop is broken. PyTasklet_Kill(t) decrefs t->tempval. This can run code. If this code releases the GIL, tasklet t might run and t->cstate might change and cs gets finalized.

@ghost
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ghost commented Dec 12, 2016

Original comment by Anselm Kruis (Bitbucket: akruis, GitHub: akruis):

Fixed. The code now uses separate loops to first identify the tasklets to bee killed and to actually kill them.

Changesets:

  • 2.7-slp: f7deec7
  • 3.3-slp: f6d12b1
  • 3.4-slp: ff54e14
  • default-slp: 9cc4d47

@ghost ghost added this to the 2.7.13-slp milestone Sep 24, 2017
@ghost ghost closed this as completed Sep 24, 2017
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