Hi Russel,
On Thu, Dec 23, 2021 at 11:48:13AM +1100, luv-main wrote:
> Below is part of the strace of gwenview (the KDE image viewer program) which
> hangs for 50 seconds on startup while waiting for a futex. How can I discover
> what this futex is about? This started just after I rebooted my workstation
> to the 5.10.0-10-amd64 kernel from the recent Debian/Bullseye update. The
> system is running mostly Bullseye with a few packages from Testing including
> libc6 which may be related to the problem (an almost identical system with the
> Bullseye libc6 is fine).
>
> Any ideas on how to investigate this?
>
> bind(14, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=0x000002}, 12) = 0
> getsockname(14, {sa_family=AF_NETLINK, nl_pid=35827, nl_groups=0x000002},
> [12]) = 0
> write(5, "\1\0\0\0\0\0\0\0", 8) = 8
> write(7, "\1\0\0\0\0\0\0\0", 8) = 8
> futex(0x7ffcf7c1b0d0, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
> write(5, "\1\0\0\0\0\0\0\0", 8) = 8
> write(7, "\1\0\0\0\0\0\0\0", 8) = 8
> futex(0x7f2794eeeb80, FUTEX_WAKE_PRIVATE, 1) = 1
> futex(0x7ffcf7c1af00, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
> write(7, "\1\0\0\0\0\0\0\0", 8) = 8
> futex(0x55f8143690c0, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
> futex(0x55f814369070, FUTEX_WAKE_PRIVATE, 1) = 0
> write(7, "\1\0\0\0\0\0\0\0", 8) = 8
> futex(0x7f2794eeeb80, FUTEX_WAKE_PRIVATE, 1) = 1
> futex(0x7ffcf7c1ad80, FUTEX_WAIT_PRIVATE, 0, NULL) = 0
> write(7, "\1\0\0\0\0\0\0\0", 8) = 8
> futex(0x7f2794eeeb80, FUTEX_WAKE_PRIVATE, 1) = 1
> futex(0x7ffcf7c1ad80, FUTEX_WAIT_PRIVATE, 0, NULL) = -1 EAGAIN (Resource
> temporarily unavailable)
> write(7, "\1\0\0\0\0\0\0\0", 8) = 8
> futex(0x55f81438d020, FUTEX_WAIT_PRIVATE, 0, NULL
>
> After 50 seconds gwenview starts up normally and displays the following
> messages which may or may not be related to the problem:
>
> QObject::connect: No such signal QDBusAbstractInterface::DeviceAdded(QString)
> QObject::connect: No such signal
> QDBusAbstractInterface::DeviceRemoved(QString)
> org.kde.kdegraphics.gwenview.lib: Unresolved raw mime type "image/x-nikon-
> nrw"
> org.kde.kdegraphics.gwenview.lib: Unresolved raw mime type "image/x-samsung-
> srw"
>
I think you need to use *strace -f*. This will show system calls from all
threads.
FUTEX_WAIT_PRIVATE can only wait for another thread in your process, so 'strace
-f' should show the other thread's wait on the same futex.
The 50s delay sounds to me like an unsuccessful DNS lookup. Maybe the other
thread did one - 'strace -f' should show that.
HTH
Cheers ... Duncan.
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