Version:            (using KDE 4.2.1)
Compiler:          gcc 4.3.3-3 (from Debian testing) 
OS:                Linux
Installed from:    Debian testing/unstable Packages

kio_http seem to hang when when it receives "HTTP/1.1 401 Malformed security token" responses while consuming increasing amount of cpu time: I had 15 kio_http processing running, while 2 used ~10% cpu each when I noticed it. Over the course of a few hours this increased to ~50% per process.

Attaching gdb to one of the processes resulted in the following two backtraces:

$ gdb attach 25143
[...]
(gdb) bt
#0  0xb7f74b7d in QCoreApplicationPrivate::removePostedEvents_unlocked (receiver=0x9bd9440, eventType=0, data=0x8cf7a88) at kernel/qcoreapplication.cpp:1301
#1  0xb7f8be12 in ~QObject (this=0x9bd9440) at kernel/qobject.cpp:890
#2  0xb7f0a438 in ~QIODevice (this=0x9bd9440) at io/qiodevice.cpp:395
#3  0xb7ef5a1d in ~QBuffer (this=0x9bd9440) at io/qbuffer.cpp:199
#4  0xb7ef6155 in ~QDataStream (this=0xbf985b08) at io/qdatastream.cpp:320
#5  0xb79d88b7 in KIO::SlaveBase::infoMessage (this=0xbf986178, _msg=@0xbf985d0c) at ../../kio/kio/slavebase.cpp:640
#6  0xb6067a1e in HTTPProtocol::sendQuery (this=0xbf986170) at ../../../kioslave/http/http.cpp:2440
#7  0xb6071677 in HTTPProtocol::proceedUntilResponseHeader (this=0xbf986170) at ../../../kioslave/http/http.cpp:565
#8  0xb6072a1e in HTTPProtocol::proceedUntilResponseContent (this=0xbf986170, dataInternal=false) at ../../../kioslave/http/http.cpp:536
#9  0xb6073791 in HTTPProtocol::post (this=0xbf986170, url=@0xbf985fc8) at ../../../kioslave/http/http.cpp:1375
#10 0xb6073cb6 in HTTPProtocol::special (this=0xbf986170, data=@0xbf986130) at ../../../kioslave/http/http.cpp:3865
#11 0xb79e0a36 in KIO::SlaveBase::dispatch (this=0xbf986178, command=77, data=@0xbf986130) at ../../kio/kio/slavebase.cpp:1159
#12 0xb79df44c in KIO::SlaveBase::dispatchLoop (this=0xbf986178) at ../../kio/kio/slavebase.cpp:282
#13 0xb605aa5b in kdemain (argc=4, argv=0x8d1c508) at ../../../kioslave/http/http.cpp:110
#14 0x0804dce1 in launch (argc=4, _name=0x8d1c8ec "kio_http", args=0x8d1c96b "", cwd=0x0, envc=0, envs=0x8d1c970 "", reset_env=false, tty=0x0,
    avoid_loops=false, startup_id_str=0x8050a03 "0") at ../../kinit/kinit.cpp:692
#15 0x0804e41d in handle_launcher_request (sock=7) at ../../kinit/kinit.cpp:1273
#16 0x0804e93a in handle_requests (waitForPid=0) at ../../kinit/kinit.cpp:1466
#17 0x0804f0ac in main (argc=2, argv=0xbf986a34, envp=0xbf986a40) at ../../kinit/kinit.cpp:1951
(gdb) continue
Continuing.
^C
Program received signal SIGINT, Interrupt.
[Switching to Thread 0xb61f3b00 (LWP 25143)]
0xb806a424 in __kernel_vsyscall ()
(gdb) bt
#0  0xb806a424 in __kernel_vsyscall ()
#1  0xb6a673d3 in write () from /lib/i686/cmov/libc.so.6
#2  0xb67f91f1 in ?? () from /usr/lib/libQtNetwork.so.4
#3  0xb67e3078 in ?? () from /usr/lib/libQtNetwork.so.4
#4  0xb67f179c in ?? () from /usr/lib/libQtNetwork.so.4
#5  0xb67f1b36 in ?? () from /usr/lib/libQtNetwork.so.4
#6  0xb67f29bd in QAbstractSocket::waitForBytesWritten () from /usr/lib/libQtNetwork.so.4
#7  0xb78ece6b in KIO::SocketConnectionBackend::sendCommand (this=0x8da8690, task=@0xbf9859b8) at ../../kio/kio/connection.cpp:294
#8  0xb78ecc53 in KIO::Connection::sendnow (this=0x8da604c, _cmd=26, data=@0xbf985a58) at ../../kio/kio/connection.cpp:502
#9  0xb78ed9ef in KIO::Connection::send (this=0x8da604c, cmd=26, data=@0xbf985a58) at ../../kio/kio/connection.cpp:486
#10 0xb79d7fdd in KIO::SlaveBase::send (this=0xbf986178, cmd=26, arr=@0xbf985a58) at ../../kio/kio/slavebase.cpp:1330
#11 0xb79d88af in KIO::SlaveBase::infoMessage (this=0xbf986178, _msg=@0xbf985b0c) at ../../kio/kio/slavebase.cpp:640
#12 0xb605b1fa in HTTPProtocol::sendBody (this=0xbf986170) at ../../../kioslave/http/http.cpp:3742
#13 0xb60679c4 in HTTPProtocol::sendQuery (this=0xbf986170) at ../../../kioslave/http/http.cpp:2438
#14 0xb6071677 in HTTPProtocol::proceedUntilResponseHeader (this=0xbf986170) at ../../../kioslave/http/http.cpp:565
#15 0xb6072a1e in HTTPProtocol::proceedUntilResponseContent (this=0xbf986170, dataInternal=false) at ../../../kioslave/http/http.cpp:536
#16 0xb6073791 in HTTPProtocol::post (this=0xbf986170, url=@0xbf985fc8) at ../../../kioslave/http/http.cpp:1375
#17 0xb6073cb6 in HTTPProtocol::special (this=0xbf986170, data=@0xbf986130) at ../../../kioslave/http/http.cpp:3865
#18 0xb79e0a36 in KIO::SlaveBase::dispatch (this=0xbf986178, command=77, data=@0xbf986130) at ../../kio/kio/slavebase.cpp:1159
#19 0xb79df44c in KIO::SlaveBase::dispatchLoop (this=0xbf986178) at ../../kio/kio/slavebase.cpp:282
#20 0xb605aa5b in kdemain (argc=4, argv=0x8d1c508) at ../../../kioslave/http/http.cpp:110
#21 0x0804dce1 in launch (argc=4, _name=0x8d1c8ec "kio_http", args=0x8d1c96b "", cwd=0x0, envc=0, envs=0x8d1c970 "", reset_env=false, tty=0x0,
    avoid_loops=false, startup_id_str=0x8050a03 "0") at ../../kinit/kinit.cpp:692
#22 0x0804e41d in handle_launcher_request (sock=7) at ../../kinit/kinit.cpp:1273
#23 0x0804e93a in handle_requests (waitForPid=0) at ../../kinit/kinit.cpp:1466
#24 0x0804f0ac in main (argc=2, argv=0xbf986a34, envp=0xbf986a40) at ../../kinit/kinit.cpp:1951

Trying to debug this with help of christoph4 did not gave more results:

(gdb) break ../../../kioslave/http/http.cpp:566
Breakpoint 1 at 0xb60715f1: file ../../../kioslave/http/http.cpp, line 566.
(gdb) break ../../../kioslave/http/http.cpp:577
Breakpoint 2 at 0xb6071606: file ../../../kioslave/http/http.cpp, line 577.
(gdb) break ../../../kioslave/http/http.cpp:580
Breakpoint 3 at 0xb607160f: file ../../../kioslave/http/http.cpp, line 580.
(gdb) continue
Continuing.

Program exited normally.

A list of open files before the exit of the program gave (among others):
$ lsof |grep 25143
kio_http  25143 mheinzes   21u     IPv4     568298       0t0    TCP 160.129.138.82:49497->qw-in-f118.google.com:www (ESTABLISHED)

I will send the captured network traffic showing the "HTTP/1.1 401 Malformed security token" responses in a follow-up mail to the bug report.

Regards,
Sten