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bin/41766: system will hang in reboot or shutdown if tmpfs contains more data than phys mem available
>Synopsis: system will hang in reboot or shutdown if tmpfs contains more
>data than phys mem available
>Arrival-Date: Wed Jul 22 12:45:00 +0000 2009
>Originator: Wolfgang Stukenbrock
>Release: NetBSD 4.0
Dr. Nagler & Company GmbH
System: NetBSD s012 4.0 NetBSD 4.0 (NSW-S012) #9: Fri Mar 13 12:31:52 CET 2009
During reboot or shutdown the last step is to execute /etc/rc.d/swap1
"swapoff=YES" is set in rc.conf. Setting this is required if the swap
on a raid device to avoid rebuilding the parity on every boot.
If there are some tmpfs filesystems, the data of theese resides in the
swap space and
if there is a large amount of data present, unmounting of the swap
space will fail.
The system will hang.
Setup a large swap space, add a tmpfs, fill e.g. twice the amount of
data of the phys memory
available in the system into the tmpfs.
Set swapoff=YES in rc.conf and try to reboot the system. You will get
The fix below simply removes all tmpfs filesystems prior unmounting the
The fix is added to swap1 that is executed as last script according to
the rcorder output
created in rc.shutdown.
remark: If someone is using network swap space it may be already too
late to do it here,
but umounting in the swap2 script would happen too early and
some problems with
still running processes may pop up.
It is clear that this fix will not solve all possible problems with
"out of swap space" during
shutdown. E.g. if there is more memroy allocated to processes than phys
memory is available,
this fix will help nothing. but in this case the kernel itself tries to
work around the problem
by killing some processes.
The following patch will add the removeal of all tmpfs filesystems in
in front of the swapspace removal.
--- swap1 2009/07/22 12:32:13 1.1
+++ swap1 2009/07/22 12:32:24
@@ -29,6 +29,16 @@
if checkyesno swapoff || [ -n "$rc_force" ]; then
echo "Removing block-type swap devices"
+# Check if there is tmpfs present.
+# The problem is that we my hang in swapctl -U if there
+# is not enougth physical memory to hold the contents.
+# Remark: We assume that there are no other mount points inside of tmpfs
+# and this will not solve the problem for more process memory
+# than physical memory.
+ umount -aft tmpfs
swapctl -U -t blk
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