AFAIK, those three contexts that you mentioned are indeed the only contexts that an 'instruction' can be in. If you look at the top-voted answer on the stackoverflow question that you cited, it explains how a kernel thread executes kernel instructions in a process context. The idea of a 'thread' in Linux is very similar to that of a process. In fact, every 'thread' _is_ a process. Just that a 'thread'/'process' happens to share some resources with other threads/process (ex. stack, text section etc.).
A kernel thread in addition has _no_ user-space addresses. The 'mm' pointer (which points to the user-space addresses of a process) is set to NULL for kernel threads. That is okay, because kernel threads are _not_ supposed to execute/access anything that might belong to a process/lies in user-space.
For details, refer Linux Kernel Dev. by Robert Love.
~Gaurav
--
On Mon, Oct 8, 2012 at 12:42 PM, Robert P. J. Day <rpjday@xxxxxxxxxxxxxx> wrote:
the standard explanation of context related to linux is that there
are three "contexts" one can be in at any time:
* user context
* kernel, process context
* kernel, interrupt context
but that's clearly(?) an incomplete (or not refined enough) list,
since it doesn't include kernel threads, and a quick google showed
this:
http://stackoverflow.com/questions/9389688/in-what-context-kernel-thread-runs-in-linux
so is there a more refined or up-to-date list of contexts which
explains them fairly well, including the subtle distinctions? thanks.
rday
--
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Robert P. J. Day Ottawa, Ontario, CANADA
http://crashcourse.ca
Twitter: http://twitter.com/rpjday
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Gaurav Jain
Associate Software Engineer
VxVM Escalations Team, SAMG
Symantec Software India Pvt. Ltd.
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