[Lse-tech] locking document available for review soon

[Rick L. <ne...@se...>]

I've produced the first draft of a document which can begin to describe
the locks in use in the Linux kernel, and I encourage the LSE community
to review it and send me comments. I've asked the maintainers of the
project to place it in a public location there so it can be easily
viewed.  Although it's in plain text right now, it's over 1900 lines
long or I'd just include it in this message.)

The philosophy of why I feel this document is necessary is explained in
the first few paragraphs of the document itself, so I won't repeat it
here. The document itself is more of a reference document than a paper,
but that's intentional for the first draft.  Once we establish the
"correct" use of the various locks in use in the system, we can then
spend time discussing incorrect or unnecessary usages. Before we agree
on "correct" usage, such discussions can become quite philosophical.

The goal of the review process, though, is to insure accuracy while
minimizing the impact to any one developer. Many of you who have
volunteered have other irons in the fire, and I want to use your time
efficiently. So I emphasize that I'm not asking any one person to
review the entire document -- please review those locks that you
believe you understand already and verify that I've interpreted them
correctly. Note that the r/w locks are only half finished; although I
believe there's only a few more hours work there, I really wanted to
get this out NOW and avoid putting it off while working on "just one
more thing."

The remaining uses of the Big Kernel Lock are especially enigmatic.  If
anyone feels qualified to comment on any remaining, legitimate uses for
the BKL, please do elaborate. My default belief, right now, is that all
the current uses are either incorrect, unnecessary, or due to be so
very soon (although I've not inserted this opinion into the document
quite so succinctly.)

One more topic I encourage you to comment on is support. My original
intention was that this become a document submitted for inclusion in
usr/src/Documentation, and that it then be maintained on an ongoing basis
either by myself or another. (Yes I volunteer, initially.)  If you have
thoughts on format, enhancements, or support issues please do include
that in your comments.  Simply to provide a starting point, I'll take the
position right now that it be updated no more frequently than quarterly
and quite possibly less frequently. Updates will necessarily follow any
new release by a minimum of six weeks since I can't make the document
correct for any particular release until it is out and I have time to
go through it (or unless the release waits for me and I'm quite happy
to have Linux be the final gate on release thank you.) If you have other
thoughts or desires on support, by all means -- dissuade me. I'm fairly
open on this.

Please send comments to ne...@se....  If that address causes
you problems for some reason, please try ne...@us....  That
address cannot reliably accept diffs currently due to possible message
reformatting, so a third address you may try if you need that
capability is ri...@ea....

Thank you in advance for your efforts. I encourage you to return
comments by 6/1 but will accept them both sooner and later.

Rick Lindsley
IBM Linux Technology Center
ne...@se...
ne...@us...
ri...@ea...