[Bug 202420] Unmount Of Swap Files At Reboot Fails

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Tue Dec 27 23:35:27 UTC 2016


https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=202420

Jilles Tjoelker <jilles at FreeBSD.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jilles at FreeBSD.org

--- Comment #1 from Jilles Tjoelker <jilles at FreeBSD.org> ---
It looks like this situation occurs only with manually added swap devices
(including swap files) and not with swap devices added by /etc/rc.d/swap and
/etc/rc.d/swaplate, since no writable filesystems are available when
/etc/rc.d/swap runs and /etc/rc.d/swaplate removes any "late" devices it added
when the system is shut down.

Note that swapoff -a looks at /etc/fstab, not at the currently active swap
devices (as would be shown by swapinfo).

If additional logic is desired to turn off (some of the) active swap devices,
it should probably be in init(8) (and reboot(8)) or in the kernel, so it
executes after all other processes have terminated and the resulting I/O is
minimized. It might be useful to non-forcibly unmount tmpfs (or all) mounts
first.

The actual panic with the usual information may be interesting as well.
Normally, a failure to read from swap causes the affected process(es) to crash
with SIGBUS (but things might be different for pageable kernel memory such as
pipe buffers and execve arguments, or if a process has been swapped out and the
kernel stack cannot be read back from swap).

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