[Bug 200493] Killing pid 11 (idle) wedges the disk IO

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=200493

--- Comment #8 from Konstantin Belousov <kib at FreeBSD.org> ---
(In reply to Konstantin Belousov from comment #7)
And to express my opinion on the whole stuff.

The signal delivery to the kernel threads must be opt-in feature.  Kernel
thread should explicitely declare the ability to handle signals directed to it.
 E.g., nfsd threads check for signal as an indication of exit request.

Most threads do not handle signals at all, and queuing the signal to them
causes odd side-effects.  Most innocent consequence is the memory leak due to
queued ksiginfo, which is never deleted from the sigqueue.  Or, the priority
bump for the idle thread, as you discovered.

Code to prevent even queuing signals to the kernel threads is trivial, but it
requires careful examination of each call to kproc/kthread creation to decide
should the signalling be allowed.  The patch I provided IMO is good stop-gap
measure which fixes the immediate ugly case.

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