[issue19337] MMAP: Bus error (core dump) under heavy read/write

2013-10-21 Thread Ribhi Kamal 

New submission from Ribhi Kamal:

I was about to use memory mapping for something when I discovered that the code 
example posted on python.org causes python to core dump. %100 reproducible

The steps are really simple. 
1- Create a file and map it using mmap.mmap
2- In a while loop, contintously read the file
3- From another process, like bash, continuously write to the file.

After about 5 iterations from the reader, python core dumps.

Reader code (python):
#!/usr/bin/python2.7

import mmap
import time

with open(hello.txt, wb) as f:
f.write(Hello Python! 1234123412341234\n)

with open(hello.txt, r+b) as f:
# memory-map the file, size 0 means whole file
mm = mmap.mmap(f.fileno(), 0)
count=0
while count  100:
   mm.seek(0)
   print mm.readline()
   time.sleep(0.1)
   count = count + 1

# close the map
mm.close()


Writer code (linux shell/bash):
#!/bin/bash
count=0
while true
do
 ((count++))
 echo $count  hello.txt
done


Now run the reader, then launch the writer in a terminal. In my case I get the 
following output:
110

462

Bus error (core dumped)


Python 2.7.3
Linux 3.2.0-54-generic #82-Ubuntu SMP Tue Sep 10 20:09:12 UTC 2013 i686 i686 
i386 GNU/Linux
Ubuntu 12.04.3 LTS
Intel(R) Core(TM)2 CPU  6300  @ 1.86GHz

--
components: IO
messages: 200820
nosy: rbhkamal
priority: normal
severity: normal
status: open
title: MMAP: Bus error (core dump) under heavy read/write
type: crash
versions: Python 2.7

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[issue19337] MMAP: Bus error (core dump) under heavy read/write

2013-10-21 Thread STINNER Victor 

Changes by STINNER Victor victor.stin...@gmail.com:


--
nosy: +haypo, neologix, pitrou, sbt

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[issue19337] MMAP: Bus error (core dump) under heavy read/write

2013-10-21 Thread Ribhi Kamal 

Ribhi Kamal added the comment:

Code dump attached

--
Added file: http://bugs.python.org/file32285/core.gz

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[issue19337] MMAP: Bus error (core dump) under heavy read/write

2013-10-21 Thread Serhiy Storchaka 

Serhiy Storchaka added the comment:

Confirm on 2.7 and 3.x.

--
components: +Library (Lib)
nosy: +serhiy.storchaka
versions: +Python 3.3, Python 3.4

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[issue19337] MMAP: Bus error (core dump) under heavy read/write

2013-10-21 Thread Charles-François Natali 

Charles-François Natali added the comment:

 3- From another process, like bash, continuously write to the file.

That's the problem: reducing (actually truncating in your case) a file 
currently mmaped *can only result in a core dump*: when you try to read from a 
location in memory which doesn't correspond anymore to a position in the file 
(since it got truncated), which value could the kernel return?

The page you're trying to read from isn't mapped anymore, so you get a segfault.

Apparently it's even documented in the main page:

The effect of changing the size of the underlying file of a mapping on the 
pages that correspond to added or removed regions of
   the file is unspecified.


--
resolution:  - invalid
stage:  - committed/rejected
status: open - closed

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[issue19337] MMAP: Bus error (core dump) under heavy read/write

2013-10-21 Thread Ribhi Kamal 

Ribhi Kamal added the comment:

I figured I was doing something wrong... sorry about that

--
components:  -Library (Lib)
resolution: invalid - 
status: closed - open
versions:  -Python 3.3, Python 3.4

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[issue19337] MMAP: Bus error (core dump) under heavy read/write

2013-10-21 Thread Ribhi Kamal 

Changes by Ribhi Kamal rbhka...@gmail.com:


--
status: open - closed

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[issue19337] MMAP: Bus error (core dump) under heavy read/write

2013-10-21 Thread Ribhi Kamal 

Changes by Ribhi Kamal rbhka...@gmail.com:


Removed file: http://bugs.python.org/file32285/core.gz

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[issue19337] MMAP: Bus error (core dump) under heavy read/write

2013-10-21 Thread Jesús Cea Avión 

Changes by Jesús Cea Avión j...@jcea.es:


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nosy: +jcea

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