[issue1984] hammer mount fails after crash - HAMMER: FIFO record bad head signature ..

[Matthew Dillon]

:New submission from Thomas Nikolajsen <thomas.nikolajsen at mail.dk>:
:
:On master from February 6th, I had a system freeze during 'hammer cleanup'
:on a x86_64 system using SMP kernel. System stopped responding on console and
:network (e.g. escape to debugger didnt work).

    It's definitely a software bug somewhere.  How big is the filesystem?
    The REDO range is 108MB and might have underflowed the undo/redo FIFO,
    which is a condition I check for but which I've never been able to test.

    The filesystem itself is probably fine, an inability to run REDOs doesn't
    mess anything up (it just means the REDOs couldn't be run).  So I think
    we can get the R/W mount working again by changing the fatal error to
    a non-fatal error:

	fetch http://apollo.backplane.com/DFlyMisc/hammer26.patch

:This file system doesn't contain any valuable data.
:
: -thomas

    If possible before you wipe the filesystem and BEFORE you do a R/W
    mount, could you run the following command on it and redirect the output
    to a file and throw it onto leaf?  That may help me figure out what is
    going on.

	hammer -f <device-from-fstab> show-undo

    Once you've done that I would appreciate it if you could try a kernel
    w/ the above specified patch, see if you can mount the filesystem R+W,
    and continue using it.

						-Matt