17b86f7fce
1 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
WANG Chao
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002337c671 |
Introduce kdump error handling service
Now upon failure kdump script might not be called at all and it might
not be able to execute default action. It results in a hang.
Because we disable emergency shell and rely on kdump.sh being invoked
through dracut-pre-pivot hook. But it might happen that we never call
into dracut-pre-pivot hook because certain systemd targets could not
reach due to failure in their dependencies. In those cases error
handling code does not run and system hangs. For example:
sysroot-var-crash.mount --> initrd-root-fs.target --> initrd.target \
--> dracut-pre-pivot.service --> kdump.sh
If /sysroot/var/crash mount fails, initrd-root-fs.target will not be
reached. And then initrd.target will not be reached,
dracut-pre-pivot.service wouldn't run. Finally kdump.sh wouldn't run.
To solve this problem, we need to separate the error handling code from
dracut-pre-pivot hook, and every time when a failure shows up, the
separated code can be called by the emergency service.
By default systemd provides an emergency service which will drop us into
shell every time upon a critical failure. It's very convenient for us to
re-use the framework of systemd emergency, because we don't have to
touch the other parts of systemd. We can use our own script instead of
the default one.
This new scheme will overwrite emergency shell and replace with kdump
error handling code. And this code will do the error handling as needed.
Now, we will not rely on dracut-pre-pivot hook running always. Instead
whenever error happens and it is serious enough that emergency shell
needed to run, now kdump error handler will run.
dracut-emergency is also replaced by kdump error handler and it's
enabled again all the way down. So all the failure (including systemd
and dracut) in 2nd kernel could be captured, and trigger kdump error
handler.
dracut-initqueue is a special case, which calls "systemctl start
emergency" directly, not via "OnFailure=emergency". In case of failure,
emergency is started, but not in a isolation mode, which means
dracut-initqueue is still running. On the other hand, emergency will
call dracut-initqueue again when default action is dump_to_rootfs.
systemd would block on the last dracut-initqueue, waiting for the first
instance to exit, which leaves us hang. It looks like the following:
dracut-initqueue (running)
--> call dracut-emergency:
--> dracut-emergency (running)
--> kdump-error-handler.sh (running)
--> call dracut-initqueue:
--> blocking and waiting for the original instance to exit.
To fix this, I'd like to introduce a wrapper emergency service. This
emegency service will replace both the systemd and dracut emergency. And
this service does nothing but to isolate to real kdump error handler
service:
dracut-initqueue (running)
--> call dracut-emergency:
--> dracut-emergency isolate to kdump-error-handler.service
--> dracut-emergency and dracut-initqueue will both be stopped
and kdump-error-handler.service will run kdump-error-handler.sh.
In a normal failure case, this still works:
foo.service fails
--> trigger emergency.service
--> emergency.service isolates to kdump-error-handler.service
--> kdump-error-handler.service will run kdump-error-handler.sh
Signed-off-by: WANG Chao <chaowang@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>
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