Re: Consistent file system hang with RELENG_6 of today ...

From: Robert Watson (rwatson_at_FreeBSD.org)
Date: 07/29/05

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    Date: Fri, 29 Jul 2005 14:19:33 +0100 (BST)
To: "Marc G. Fournier" <scrappy@hub.org>

    On Fri, 29 Jul 2005, Marc G. Fournier wrote:

    > Oh, before I forget ... how do you break to DDB from a serial console?
    > I'll be running a Portmaster for this ...

    Compile BREAK_TO_DEBUGGER into the kernel. Then issue a serial break and
    it should go into the debugger if the low-level console is set to the
    serial port.

    On my port-master, I issue a telnet break using "send break" after hitting
    ^] to generate a serial break for a serial port hooked up to TCP.

    There's also ALT_BREAK_TO_DEBUGGER, which is documented in NOTES, and
    provides for an alternative key sequence that doesn't use a break signal.

    Robert N M Watson

    >
    > On Fri, 29 Jul 2005, Robert Watson wrote:
    >
    >>
    >> On Thu, 28 Jul 2005, Marc G. Fournier wrote:
    >>
    >>> 'k, I'm starting to play with 6.x, for our new server ... my priority
    >>> right now is to just have it run the existing 'jail' environments from my
    >>> 4.x machine, while I work on getting all of our servers up to 6.x, and
    >>> then will worry about the jail's themselves ...
    >>>
    >>> When I try and startup the 4.x jail on my 6.x machine, it "hangs" the file
    >>> system that the jail directory hierarchy happens to be mounted on though
    >>> ... twice in a row so far ...
    >>>
    >>> Now, I'm suspecting (and am going to try without it) that it might be
    >>> because I'm mounting devfs within the 4.x jail, but even then, it
    >>> shouldn't hang things up, only generate a whack of errors ...
    >>>
    >>> I have a good dump (CTL-ALT-ESC -> panic), but do not have a clue what to
    >>> offer from within there that might be of any use ...
    >>>
    >>> If anyone is interested ... ?
    >>
    >> If you can get into DDB and have serial console output, the following would
    >> be useful:
    >>
    >> The output of 'show pcpu'
    >>
    >> The output of 'show pcpu X' for each present cpu, starting with 0.
    >>
    >> The output of 'ps'
    >>
    >> The output of 'trace' for the currently running thread, and each non-idle
    >> thread shown in the show pcpu output
    >>
    >> The output of 'show lockedvnods'
    >>
    >> It would also be useful if, relating to the startup of the jail, you can
    >> identify the point in the jail boot where it wedges, and if you hit Ctrl-T,
    >> what process is shown as running and what state it is in, and using DDB,
    >> trace that process.
    >>
    >> If you could show the trace output for each process listed in "show
    >> lockevnods".
    >>
    >> Likely, there is a leaked lock or a low buffer condition. However, once we
    >> have the above output we should be able to say more. The above will
    >> hopefully tell us whether it's a vnode deadlock, and ideally, the
    >> approximate source.
    >>
    >> Robert N M Watson
    >>
    >>
    >
    > ----
    > Marc G. Fournier Hub.Org Networking Services (http://www.hub.org)
    > Email: scrappy@hub.org Yahoo!: yscrappy ICQ: 7615664
    >
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