Hello,
I'm trying to kill a kernel thread gracefully, in particular kswapd,
without any success.
The goal is to start another kernel thread that contains updated kswapd
functionality, through a loadable module; no kernel recompilation.
I noticed that kernel threads block SIGKILL. Hence, on module load I'm
running:
task = find_task_by_name("kswapd");
if (task != NULL) {
spin_lock_irq(&task->sigmask_lock);
sigdelset(&task->blocked, SIGKILL);
recalc_sigpending(task);
spin_unlock_irq(&task->sigmask_lock);
// Also tried issuing here a: kill_proc(task->pid, SIGKILL, 1);
}
Then from userspace I issue:
# ps aux |grep -i swap
root 4 0.0 0.0 0 0 ? SW 18:36 0:00 [kswapd]
$ kill -9 4
After the kill is issued, kswapd is taking up 99.9% of CPU time and
remains at a runnable state:
# ps aux |grep -i swap
root 4 0.2 0.0 0 0 ? RW 18:36 0:02 [kswapd]
Can anyone explain why this is happening ? I've tried this with linux
kernels 2.2.19 and 2.4.27 (with patch kdb-4.3). What is the proper way
of gracefully killing a kernel thread launched from the original kernel
image (not a module) in kernels < 2.6 (ie. without the new kernel thread
API that contains the stop_kthread call documented in
http://www.scs.ch/~frey/linux/kernelthreads.html)
I've also tried the same with kflushd, kupdate, and keventd in 2.2.19.
When I do issue a "kill -9" for them I see:
# ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 2 0.0 0.0 0 0 ? SW 12:18 0:00 [kflushd]
root 3 1.5 0.0 0 0 ? RW 12:18 0:16 [kupdate]
root 5 0.0 0.0 0 0 ? SW 12:18 0:00 [keventd]
All 3 kernel threads remain in the process list. kupdate also appears to
be in a running state consuming 99.9% of the CPU when killed. What's so
special about kupdate and kswapd that makes them stay at a running
state, and why do all kernel threads seem unkillable?
Thanks,
Kristis
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