printing a list releases the GIL carelessly

[pitrou]

BPO	7084
Nosy	@pitrou
Files	list_print.py list_print-r75317.patch: guard from the crash by grabbing a reference before releasing the GIL

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/pitrou'
closed_at = <Date 2009-10-27.13:10:15.046>
created_at = <Date 2009-10-08.21:35:07.646>
labels = ['type-crash']
title = 'printing a list releases the GIL carelessly'
updated_at = <Date 2009-10-27.13:10:15.044>
user = 'https://github.com/pitrou'

bugs.python.org fields:

activity = <Date 2009-10-27.13:10:15.044>
actor = 'pitrou'
assignee = 'pitrou'
closed = True
closed_date = <Date 2009-10-27.13:10:15.046>
closer = 'pitrou'
components = []
creation = <Date 2009-10-08.21:35:07.646>
creator = 'pitrou'
dependencies = []
files = ['15083', '15099']
hgrepos = []
issue_num = 7084
keywords = ['patch']
message_count = 4.0
messages = ['93764', '93846', '93875', '94557']
nosy_count = 2.0
nosy_names = ['scott.dial', 'pitrou']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue7084'
versions = ['Python 2.6']

[pitrou]

Function list_print() in listobject.c releases the GIL before calling
fprintf() but doesn't check the list size again when it gets the GIL
back. If another thread truncated the list, a crash can ensue. The
attached script crashes reliably here.

[scottdial]

I've attached a patch that fixes this issue by grabbing a reference to
the item to be printed just before releasing the GIL.

[pitrou]

Thank you! The patch has been committed in trunk in r75367. I am waiting
for the 2.6 branch to unfreeze before backporting it.

[pitrou]

Backported to 2.6 in r75750.