Public bug reported:
Steps to reproduce
Login as user1
Login as user2
Press Ctrl+Alt+F7 (to switch to first user)
kwin from second user starts to eat 100% of cpu.
Here is my investigation of what is going on
1) ====== GDB ======
I attached to running (and eating 100% of cpu) kwin, paused ("ctrl+c" command)
and run ("continue" command) kwin several times and watched output of info
threads command to figure out what thread is eating 100%.
What I got:
(gdb) info threads
Id Target Id Frame
3 Thread 0x7fa21ecb6700 (LWP 25128) "QProcessManager" 0x00007fa23f3c8de3
in select () at ../sysdeps/unix/syscall-template.S:81
2 Thread 0x7fa21c9c6700 (LWP 25131) "kwin" pthread_cond_wait@@GLIBC_2.3.2
()
at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
* 1 Thread 0x7fa23fbfe7c0 (LWP 25123) "kwin" 0x00007fa236ea7f84 in
__GI___pthread_mutex_lock (mutex=0x2520918) at pthread_mutex_lock.c:54
(gdb) continue
// continue, wait some time, ctrl+c
(gdb) info threads
Id Target Id Frame
3 Thread 0x7fa21ecb6700 (LWP 25128) "QProcessManager" 0x00007fa23f3c8de3
in select () at ../sysdeps/unix/syscall-template.S:81
2 Thread 0x7fa21c9c6700 (LWP 25131) "kwin" pthread_cond_wait@@GLIBC_2.3.2
()
at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
* 1 Thread 0x7fa23fbfe7c0 (LWP 25123) "kwin" 0x00007fa23f3d1957 in
__libc_recv (fd=9, buf=0x2520974, n=4096, flags=-1, flags@entry=0)
at ../sysdeps/unix/sysv/linux/x86_64/recv.c:33
// continue, wait some time, ctrl+c
(gdb) info threads
Id Target Id Frame
3 Thread 0x7fa21ecb6700 (LWP 25128) "QProcessManager" 0x00007fa23f3c8de3
in select () at ../sysdeps/unix/syscall-template.S:81
2 Thread 0x7fa21c9c6700 (LWP 25131) "kwin" pthread_cond_wait@@GLIBC_2.3.2
()
at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
* 1 Thread 0x7fa23fbfe7c0 (LWP 25123) "kwin" 0x00007fa23f3c8de3 in select ()
at ../sysdeps/unix/syscall-template.S:81
and so on...
As you can see first thread is really doing something.
Now, when I know thread number I can see backtrace:
First backtrace
[Switching to thread 1 (Thread 0x7fa23fbfe7c0 (LWP 25123))]
#0 0x00007fa238b11303 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
(gdb) backtrace
#0 0x00007fa238b11303 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#1 0x00007fa2396d05ef in
QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#2 0x00007fa2396d08e5 in
QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#3 0x00007fa2396d5e5b in QCoreApplication::exec() () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#4 0x00007fa23f719956 in kdemain () from
/usr/lib/kde4/libkdeinit/libkdeinit4_kwin.so
#5 0x00007fa23f2f7de5 in __libc_start_main (main=0x4006d0, argc=3,
ubp_av=0x7ffffe010848, init=<optimized out>, fini=<optimized out>,
rtld_fini=<optimized out>, stack_end=0x7ffffe010838) at libc-start.c:260
#6 0x00000000004006fe in _start ()
// continue, wait some time, ctrl+c
And second one (after "continue" and "ctrl+c")
(gdb) backtrace
#0 0x00007fa23f3c8de3 in select () at ../sysdeps/unix/syscall-template.S:81
#1 0x00007fa2396fc33b in qt_safe_select(int, fd_set*, fd_set*, fd_set*,
timeval const*) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#2 0x00007fa239701904 in
QEventDispatcherUNIXPrivate::doSelect(QFlags<QEventLoop::ProcessEventsFlag>,
timeval*) ()
from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#3 0x00007fa239701d02 in
QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#4 0x00007fa238b112f6 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#5 0x00007fa2396d05ef in
QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#6 0x00007fa2396d08e5 in
QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#7 0x00007fa2396d5e5b in QCoreApplication::exec() () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#8 0x00007fa23f719956 in kdemain () from
/usr/lib/kde4/libkdeinit/libkdeinit4_kwin.so
#9 0x00007fa23f2f7de5 in __libc_start_main (main=0x4006d0, argc=3,
ubp_av=0x7ffffe010848, init=<optimized out>, fini=<optimized out>,
rtld_fini=<optimized out>, stack_end=0x7ffffe010838) at libc-start.c:260
#10 0x00000000004006fe in _start ()
(gdb)
2) ====== strace ======
Now lets see which syscalls are called, I ran this command
strace -p 25123 -s 1000 -o strace1.txt
And in 1-2 seconds I got file (with 50000 lines) which contains ONLY these
messages:
select(29, [4 5 9 10 14 28], [], [], {0, 0}) = 0 (Timeout)
recvfrom(9, 0x2520974, 4096, 0, 0, 0) = -1 EAGAIN (Resource temporarily
unavailable)
select(29, [4 5 9 10 14 28], [], [], {0, 0}) = 0 (Timeout)
recvfrom(9, 0x2520974, 4096, 0, 0, 0) = -1 EAGAIN (Resource temporarily
unavailable)
select(29, [4 5 9 10 14 28], [], [], {0, 0}) = 0 (Timeout)
recvfrom(9, 0x2520974, 4096, 0, 0, 0) = -1 EAGAIN (Resource temporarily
unavailable)
select(29, [4 5 9 10 14 28], [], [], {0, 0}) = 0 (Timeout)
recvfrom(9, 0x2520974, 4096, 0, 0, 0) = -1 EAGAIN (Resource temporarily
unavailable)
select(29, [4 5 9 10 14 28], [], [], {0, 0}) = 0 (Timeout)
Notice first argument of recvfrom - 9, this fd we already saw at gdb "info
threads":
* 1 Thread 0x7fa23fbfe7c0 (LWP 25123) "kwin" 0x00007fa23f3d1957 in
__libc_recv (fd=9, buf=0x2520974, n=4096, flags=-1,
ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: kde-window-manager 4:4.11.3-0ubuntu0.1
ProcVersionSignature: Ubuntu 3.11.0-15.23-generic 3.11.10
Uname: Linux 3.11.0-15-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.12.5-0ubuntu2.2
Architecture: amd64
Date: Fri Jan 24 21:20:31 2014
InstallationDate: Installed on 2013-11-11 (74 days ago)
InstallationMedia: Kubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
MarkForUpload: True
SourcePackage: kde-workspace
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: kde-workspace (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug saucy
** Description changed:
Steps to reproduce
Login as user1
Login as user2
Press Ctrl+Alt+F7 (to switch to first user)
kwin from second user starts to eat 100% of cpu.
Here is my investigation of what is going on
1) ====== GDB ======
- I attached to running (and eating 100% of cpu) kwin, paused ("ctrl+c"
command) and run ("continue" command) kwin several times and watched output of
info threads command to figure out what thread is eating 100%.
+ I attached to running (and eating 100% of cpu) kwin, paused ("ctrl+c"
command) and run ("continue" command) kwin several times and watched output of
info threads command to figure out what thread is eating 100%.
What I got:
- (gdb) info threads
- Id Target Id Frame
- 3 Thread 0x7fa21ecb6700 (LWP 25128) "QProcessManager" 0x00007fa23f3c8de3
in select () at ../sysdeps/unix/syscall-template.S:81
- 2 Thread 0x7fa21c9c6700 (LWP 25131) "kwin"
pthread_cond_wait@@GLIBC_2.3.2 ()
- at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
+ (gdb) info threads
+ Id Target Id Frame
+ 3 Thread 0x7fa21ecb6700 (LWP 25128) "QProcessManager" 0x00007fa23f3c8de3
in select () at ../sysdeps/unix/syscall-template.S:81
+ 2 Thread 0x7fa21c9c6700 (LWP 25131) "kwin"
pthread_cond_wait@@GLIBC_2.3.2 ()
+ at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
* 1 Thread 0x7fa23fbfe7c0 (LWP 25123) "kwin" 0x00007fa236ea7f84 in
__GI___pthread_mutex_lock (mutex=0x2520918) at pthread_mutex_lock.c:54
- (gdb) continue
+ (gdb) continue
// continue, wait some time, ctrl+c
- (gdb) info threads
- Id Target Id Frame
- 3 Thread 0x7fa21ecb6700 (LWP 25128) "QProcessManager" 0x00007fa23f3c8de3
in select () at ../sysdeps/unix/syscall-template.S:81
- 2 Thread 0x7fa21c9c6700 (LWP 25131) "kwin"
pthread_cond_wait@@GLIBC_2.3.2 ()
- at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
+ (gdb) info threads
+ Id Target Id Frame
+ 3 Thread 0x7fa21ecb6700 (LWP 25128) "QProcessManager" 0x00007fa23f3c8de3
in select () at ../sysdeps/unix/syscall-template.S:81
+ 2 Thread 0x7fa21c9c6700 (LWP 25131) "kwin"
pthread_cond_wait@@GLIBC_2.3.2 ()
+ at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
* 1 Thread 0x7fa23fbfe7c0 (LWP 25123) "kwin" 0x00007fa23f3d1957 in
__libc_recv (fd=9, buf=0x2520974, n=4096, flags=-1, flags@entry=0)
- at ../sysdeps/unix/sysv/linux/x86_64/recv.c:33
+ at ../sysdeps/unix/sysv/linux/x86_64/recv.c:33
// continue, wait some time, ctrl+c
- (gdb) info threads
- Id Target Id Frame
- 3 Thread 0x7fa21ecb6700 (LWP 25128) "QProcessManager" 0x00007fa23f3c8de3
in select () at ../sysdeps/unix/syscall-template.S:81
- 2 Thread 0x7fa21c9c6700 (LWP 25131) "kwin"
pthread_cond_wait@@GLIBC_2.3.2 ()
- at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
+ (gdb) info threads
+ Id Target Id Frame
+ 3 Thread 0x7fa21ecb6700 (LWP 25128) "QProcessManager" 0x00007fa23f3c8de3
in select () at ../sysdeps/unix/syscall-template.S:81
+ 2 Thread 0x7fa21c9c6700 (LWP 25131) "kwin"
pthread_cond_wait@@GLIBC_2.3.2 ()
+ at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
* 1 Thread 0x7fa23fbfe7c0 (LWP 25123) "kwin" 0x00007fa23f3c8de3 in select
() at ../sysdeps/unix/syscall-template.S:81
and so on...
As you can see first thread is really doing something.
Now, when I know thread number I can see backtrace:
First backtrace
[Switching to thread 1 (Thread 0x7fa23fbfe7c0 (LWP 25123))]
#0 0x00007fa238b11303 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
- (gdb) backtrace
+ (gdb) backtrace
#0 0x00007fa238b11303 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#1 0x00007fa2396d05ef in
QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#2 0x00007fa2396d08e5 in
QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#3 0x00007fa2396d5e5b in QCoreApplication::exec() () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#4 0x00007fa23f719956 in kdemain () from
/usr/lib/kde4/libkdeinit/libkdeinit4_kwin.so
- #5 0x00007fa23f2f7de5 in __libc_start_main (main=0x4006d0, argc=3,
ubp_av=0x7ffffe010848, init=<optimized out>, fini=<optimized out>,
- rtld_fini=<optimized out>, stack_end=0x7ffffe010838) at libc-start.c:260
+ #5 0x00007fa23f2f7de5 in __libc_start_main (main=0x4006d0, argc=3,
ubp_av=0x7ffffe010848, init=<optimized out>, fini=<optimized out>,
+ rtld_fini=<optimized out>, stack_end=0x7ffffe010838) at libc-start.c:260
#6 0x00000000004006fe in _start ()
// continue, wait some time, ctrl+c
And second one (after "continue" and "ctrl+c")
- (gdb) backtrace
+ (gdb) backtrace
#0 0x00007fa23f3c8de3 in select () at ../sysdeps/unix/syscall-template.S:81
#1 0x00007fa2396fc33b in qt_safe_select(int, fd_set*, fd_set*, fd_set*,
timeval const*) () from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#2 0x00007fa239701904 in
QEventDispatcherUNIXPrivate::doSelect(QFlags<QEventLoop::ProcessEventsFlag>,
timeval*) ()
- from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
+ from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#3 0x00007fa239701d02 in
QEventDispatcherUNIX::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) ()
- from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
+ from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#4 0x00007fa238b112f6 in ?? () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#5 0x00007fa2396d05ef in
QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#6 0x00007fa2396d08e5 in
QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#7 0x00007fa2396d5e5b in QCoreApplication::exec() () from
/usr/lib/x86_64-linux-gnu/libQtCore.so.4
#8 0x00007fa23f719956 in kdemain () from
/usr/lib/kde4/libkdeinit/libkdeinit4_kwin.so
- #9 0x00007fa23f2f7de5 in __libc_start_main (main=0x4006d0, argc=3,
ubp_av=0x7ffffe010848, init=<optimized out>, fini=<optimized out>,
- rtld_fini=<optimized out>, stack_end=0x7ffffe010838) at libc-start.c:260
+ #9 0x00007fa23f2f7de5 in __libc_start_main (main=0x4006d0, argc=3,
ubp_av=0x7ffffe010848, init=<optimized out>, fini=<optimized out>,
+ rtld_fini=<optimized out>, stack_end=0x7ffffe010838) at libc-start.c:260
#10 0x00000000004006fe in _start ()
- (gdb)
+ (gdb)
-
- 1) ====== strace ======
+ 2) ====== strace ======
Now lets see which syscalls are called, I ran this command
strace -p 25123 -s 1000 -o strace1.txt
And in 1-2 seconds I got file (with 50000 lines) which contains ONLY these
messages:
select(29, [4 5 9 10 14 28], [], [], {0, 0}) = 0 (Timeout)
recvfrom(9, 0x2520974, 4096, 0, 0, 0) = -1 EAGAIN (Resource temporarily
unavailable)
select(29, [4 5 9 10 14 28], [], [], {0, 0}) = 0 (Timeout)
recvfrom(9, 0x2520974, 4096, 0, 0, 0) = -1 EAGAIN (Resource temporarily
unavailable)
select(29, [4 5 9 10 14 28], [], [], {0, 0}) = 0 (Timeout)
recvfrom(9, 0x2520974, 4096, 0, 0, 0) = -1 EAGAIN (Resource temporarily
unavailable)
select(29, [4 5 9 10 14 28], [], [], {0, 0}) = 0 (Timeout)
recvfrom(9, 0x2520974, 4096, 0, 0, 0) = -1 EAGAIN (Resource temporarily
unavailable)
select(29, [4 5 9 10 14 28], [], [], {0, 0}) = 0 (Timeout)
-
Notice first argument of recvfrom - 9, this fd we already saw at gdb "info
threads":
* 1 Thread 0x7fa23fbfe7c0 (LWP 25123) "kwin" 0x00007fa23f3d1957 in
__libc_recv (fd=9, buf=0x2520974, n=4096, flags=-1,
ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: kde-window-manager 4:4.11.3-0ubuntu0.1
ProcVersionSignature: Ubuntu 3.11.0-15.23-generic 3.11.10
Uname: Linux 3.11.0-15-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.12.5-0ubuntu2.2
Architecture: amd64
Date: Fri Jan 24 21:20:31 2014
InstallationDate: Installed on 2013-11-11 (74 days ago)
InstallationMedia: Kubuntu 13.10 "Saucy Salamander" - Release amd64
(20131016.1)
MarkForUpload: True
SourcePackage: kde-workspace
UpgradeStatus: No upgrade log present (probably fresh install)
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https://bugs.launchpad.net/bugs/1272438
Title:
kwin 100% of cpu, second session
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