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Posted to bugs@httpd.apache.org by bu...@apache.org on 2010/11/08 19:33:22 UTC
DO NOT REPLY [Bug 50237] New: webdav LOCK access with multiple
threads to same folder causes UNLOCK failures
https://issues.apache.org/bugzilla/show_bug.cgi?id=50237
Summary: webdav LOCK access with multiple threads to same
folder causes UNLOCK failures
Product: Apache httpd-2
Version: 2.3-HEAD
Platform: PC
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P2
Component: mod_dav
AssignedTo: bugs@httpd.apache.org
ReportedBy: mikeh@elementaltechnologies.com
If multiple processes or threads are writing to unique files in the same folder
on a webdav server using LOCKS, intermittent webdav errors will occur during
the UNLOCK request.
Server configuration: Centos 5.5. Tested with Apache/2.2.3, Apache/2.2.17 and
Apache/2.3.8.
I have a custom application that uses libcurl to upload files to a webdav
server. However, I have reproduced the same problem using cadaver, a simple
script and a locally hosted Apache webdav server.
The error occurs during an UNLOCK. A 400 (bad request) is returned. Once this
failure occurs, the file remains locked. I used several methods over several
days to ensure the LOCK/PUT/UNLOCK sequences being issued are valid and contain
the correct lock token (wireshark, added custom logging to dav, etc.).
I used a patched version of cadaver that adds scripting ability so I could
automate the test.
Here is what the test does:
One shell script is repeatedly running this:
1. LOCK webdav/test/a.bin 2. PUT a.bin webdav/test/a.bin 3. UNLOCK
webdav/test/a.bin
At the same time, a second shell script is repeatedly running this (same webdav
folder, but accessing a different file):
1. LOCK webdav/test/b.bin 2. PUT b.bin webdav/test/b.bin 3. UNLOCK
webdav/test/b.bin
The test repeats anywhere from a few times to several hundred times before the
failure occurs. Below is the output from cadaver at the failure point:
Locking `webdav/test/a.bin': succeeded. Lock token
<opaquelocktoken:7ca6e55d-1bf6-4ce0-a8a4-7d97117db8af>: Depth infinity on
`http://localhost:81/webdav/test/a.bin' Scope: exclusive Type: write Timeout:
infinite Owner: Uploading a.bin to `/webdav/test/a.bin': [.......... succeeded.
Unlocking `webdav/test/a.bin': failed: 400 Bad Request
At the failure point, this message is in the Apache error_log:
(11)Resource temporarily unavailable: The locktoken specified in the
"Lock-Token:" header is invalid because this resource has no outstanding locks.
[400, #0]
I tried adding additional debug messages to dav, but have not been able to
track down why the lock is not valid. I also tried to make a debug build of
Apache so I could use gdb to help debug at least one of the scripts to better
understand the flow of the lock data, but was unable to get debug symbols in
the binary (I used the --enable-maintainer-mode configure option).
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DO NOT REPLY [Bug 50237] webdav LOCK access with multiple threads to
same folder causes UNLOCK failures
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=50237
--- Comment #3 from Mike Henry <mi...@elementaltechnologies.com> 2010-11-18 18:16:47 EST ---
I lost my PC that I was using the debug the issue. I will have to setup
everything up on another system. I will update the bug after completed.
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DO NOT REPLY [Bug 50237] webdav LOCK access with multiple threads to
same folder causes UNLOCK failures
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=50237
--- Comment #2 from Jeff Trawick <tr...@apache.org> 2010-11-10 16:02:35 EST ---
>To get more info, you could also try strace-ing httpd and see which system
>call returns 'Resource temporarily unavailable' (EAGAIN).
Mike, when you tested at trunk did you see 'Resource temporarily available'
logged?
Possibly the logging of EAGAIN is because the dav error APIs prior to httpd
2.3.4 did not take an apr_status_t parameter, and assumed errno was meaningful
for the problem at hand (and that's a common error for network I/O).
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DO NOT REPLY [Bug 50237] webdav LOCK access with multiple threads to
same folder causes UNLOCK failures
Posted by bu...@apache.org.
https://issues.apache.org/bugzilla/show_bug.cgi?id=50237
Stefan Fritsch <sf...@sfritsch.de> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |NEEDINFO
--- Comment #1 from Stefan Fritsch <sf...@sfritsch.de> 2010-11-10 15:53:21 EST ---
I could not reproduce this (neither with 2.2.16 nor with trunk).
I suspect that there may be a lock contention when accessing the dbm file that
stores the locks. Which dbm library are you using? (Try 'ldd
/usr/lib/apr-util-1/apr_dbm_db.so' or 'ldd /usr/lib/libaprutil-1.so' depending
on how you compiled it). I have Berkley DB 4.8.
To get more info, you could also try strace-ing httpd and see which system call
returns 'Resource temporarily unavailable' (EAGAIN). If it is something related
to your dav lockdb, that would give a hint. But it's also possible that it is
not related to DAV at all but a bug in the logging code.
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