IO.select hangs forever reading device files on older linux kernels

Details

Type: Bug
Status: Closed
Priority: Blocker
Resolution: Fixed
Affects Version/s: 0.5.4
Fix Version/s: 0.5.6, 0.6.4
Component/s: Block Device
Labels:
None
Environment:

Linux localhost.localdomain 2.6.18-164.el5 #1 SMP Thu Sep 3 03:28:30 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux, though other kernels of similar vintage are probably similarly affected

Description

The block device plugin has code that evaluates to this:

File.read("/sys/block/md0/size")

This uses a select() call internally:

[root@localhost ~]# strace -p 8000
Process 8000 attached - interrupt to quit
select(4, [3], [], [], NULL <unfinished ...>


lsof -p 8000
COMMAND  PID USER   FD   TYPE DEVICE     SIZE    NODE NAME
...
ruby    8000 root    3r   REG    0,0     4096    6104 /sys/block/md0/size

but the call to select() hangs forever (even though it should not):

irb(main):001:0> f=File.open("/sys/block/md0/size")
=> #<File:/sys/block/md0/size>
irb(main):002:0> IO.select([f], nil, nil, nil)
# hangs forever

So this plugin should be modified to use read_nonblock, which does not hang.

Issue Links

relates to

OHAI-366 Fix for older linux kernels and blocking read of /proc/* files in virtualization plugin

Activity

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Daniel DeLeo made changes - 16/Jun/10 9:04 PM

Field	Original Value	New Value
Environment		Linux localhost.localdomain 2.6.18-164.el5 #1 SMP Thu Sep 3 03:28:30 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux, though other kernels of similar vintage are probably similarly affected