Kernel Crash using FUSE

Hi, I'd like to report a kernel crash that I experienced using a FUSE
filesystem.

Unfortunately I have very little data to report, as I was running a test
on a server in a data center that I have no physical access to and could
not see the console output of the system to view any kernel panic
diagnostics.  All I have is syslog messages and they are not very
detailed.

Basically, I was testing out a FUSE filesystem called 's3backer', at:

http://code.google.com/p/s3backer

This FUSE filesystem exposes a single file that it stores block-by-block
in an S3 bucket.  You can use a loopback mount to then mount this file as
a filesystem, thus obtaining an S3-backed Unix filesystem.

I was testing it by using cp -a of a largish directory (4,000+ files in
the directory tree, total of about 300 MB of data), and at the same time,
running find | xargs wc -l to watch how many files had been copied.  After
a few minutes of activity, my entire system froze up.  Symptoms were that
I could not do anything that seemed to require a process to hit the
kernel's VFS layer; I found that I couldn't create any processes, but that
the kernel was still managing its TCP/IP stack (I could ping it) and I
could even make connections to existing services (the TCP/IP connection
would complete) but that I couldn't get them to do anything.

After almost 2 hours I managed to get the data center staff to reboot the
system for me.  This is all I have from syslog to describe the event:

Jul 16 23:34:32 dima s3backer: s3backer process 25251 for /tmp/testmnt
started
Jul 16 23:34:32 dima s3backer: created s3backer using
http://s3.amazonaws.com/www.ischo.com.testmnt
Jul 16 23:36:42 dima kernel: loop: loaded (max 8 devices)
Jul 16 23:43:01 dima s3backer: rec'd 500 response: PUT
http://s3.amazonaws.com/www.ischo.com.testmnt/0009e1df
Jul 16 23:43:01 dima s3backer: retrying query (attempt #2): PUT
http://s3.amazonaws.com/www.ischo.com.testmnt/0009e1df
Jul 16 23:45:25 dima s3backer: rec'd 500 response: PUT
http://s3.amazonaws.com/www.ischo.com.testmnt/0009e5e5
Jul 16 23:45:25 dima s3backer: retrying query (attempt #2): PUT
http://s3.amazonaws.com/www.ischo.com.testmnt/0009e5e5
Jul 17 01:00:52 dima syslogd 1.4.1: restart.

I was really surprised to find that a FUSE filesystem could crash the
kernel.  Doesn't FUSE, since it's dealing with a userspace program, have
stringent protections in place so that if the FUSE userspace program
misbehaves, it doesn't crash the kernel?  Or perhaps this is just a bug in
FUSE itself?

Details of my system:

Linux dima.ischo.com 2.6.20-1.2320.fc5
fusermount version: 2.6.5

(yes, it's a fairly old Fedora Core 5 system, were there maybe known bugs
in FUSE that have been fixed since then?)

Thanks!
Bryan

------------------------------------------------------------------------
Bryan Ischo                bryan@...            2001 Mazda 626 GLX
Hamilton, New Zealand      http://www.ischo.com     RedHat Fedora Core 5
------------------------------------------------------------------------



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