On Sat, 9 Apr 2016, John Baldwin wrote:
On Saturday, April 09, 2016 12:05:24 PM Bjoern A. Zeeb wrote:
Author: bz
Date: Sat Apr 9 12:05:23 2016
New Revision: 297742
URL: https://svnweb.freebsd.org/changeset/base/297742
Log:
Mfp: r296310,r296343
It looks like as with the safety belt of DELAY() fastened (*) we can
completely tear down and free all memory for TCP (after r281599).
(*) in theory a few ticks should be good enough to make sure the timers
are all really gone. Could we use a better matric here and check a
tcbcb count as an optimization?
In theory, no amount of DELAY() is ever enough to close a theoretical race
window. In practice you might get lucky, but you might also panic and
Yes I do understand. Thus saying a better metric should do the right
thing. I am aware of the consequences of removing type stability.
Should there be reports I'll make sure that DELAY becomes something
more proper sooner than later.
trash user data. In the rest of the tree, we tend to prefer marking items
as NOFREE instead of this approach putting a priority on stability and
reliability over memory efficiency.
For all of the zones that you removed NOFREE from, do you know why that was
added in the first place (e.g. which stale pointers to pcbs could be
referenced after free)? Did you verify that those conditions have been
fixed?
I did check. I did check a few years ago (and I think you had
reviewed that; maybe it was trouble). And the TCP bits here were
the last ones that were problematic back then. With the changes from
r281599 this should no longer be a problem.
As for the others, a few years ago Andre already removed the NOFREE
and we unconditionally made him back the change out, which was a
mistake as otherwise some of these zones would have been "clean" for
years. Others have had KASSERTs ensuring that on VNET stack they were
actually empty.
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