Bug 240122 - ddb: cont doesn't give a working terminal back
Summary: ddb: cont doesn't give a working terminal back
Status: New
Alias: None
Product: Base System
Classification: Unclassified
Component: kern (show other bugs)
Version: CURRENT
Hardware: Any Any
: --- Affects Some People
Assignee: freebsd-bugs (Nobody)
Depends on:
Reported: 2019-08-26 12:16 UTC by Bjoern A. Zeeb
Modified: 2020-08-05 17:28 UTC (History)
2 users (show)

See Also:


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Description Bjoern A. Zeeb freebsd_committer 2019-08-26 12:16:33 UTC
I've seen this for a long time when using ddb over an IPMI serial console and people were saying that it could be because of IPMI and whatever.

Now I had a KDB: enter: manua escape to debugger situation (unclear where from yet) on my laptop.  I said "db> cont" on v0 and it is stuck at that, not bringing back the shell session alive.   However I can switch to v1 v2 v3 and all these shells are perfectly working fine.

I wonder what is broken that returning from ddb doesn't work anymore?
Comment 1 Bjoern A. Zeeb freebsd_committer 2019-08-26 20:12:31 UTC
Coming back hours later pressing <Enter> again on the "cont" line which didn't show a shell prompt, gave me the 4 <Enter>s I pressed in total (3 earlier, 1 now) and the command prompt came back.  Something is still fishy.

Anyone else with other experience (IPMI, serial, tty) would be welcome.
Comment 2 Bjoern A. Zeeb freebsd_committer 2020-08-03 21:09:06 UTC
And I currently had this on a classic serial line machine as well.
sysctl debug.kdb.enter=1
ddb> cont

I still get kernel printfs coming but typing anything doesn't work.

I hope someone has an idea...  It's annoying if you cannot remotely power cycle a machine and need hands-on.
Comment 3 Gary Jennejohn 2020-08-05 17:28:15 UTC
(In reply to Bjoern A. Zeeb from comment #2)
I gave this a try in vt0 and, after entering cont in the ddb prompt the terminal recovered and my bash prompt reappeared.  A number of carriage returns were apparently emitted by the kernel, but that was not a problem.
BUT I'm using sc and NOT vt.  What are you using?