callout is first initialised, using a new function callout_init_mtx().
The callout system will acquire this mutex before calling the callout
function and release it on return.
In addition, the callout system uses the mutex to avoid most of the
complications and race conditions inherent in asynchronous timer
facilities, so mutex-protected callouts have much simpler semantics.
As long as the mutex is held when invoking callout_stop() or
callout_reset(), then these functions will guarantee that the callout
will be stopped, even if softclock() had already begun to process
the callout.
Existing Giant-locked callouts will automatically pick up the new
race-free semantics. This should close a number of race conditions
in the USB code and probably other areas of the kernel too.
There should be no change in behaviour for "MP-safe" callouts; these
still need to use the techniques mentioned in timeout(9) to avoid
race conditions.
when using the callout subsystem. Show how the callout_pending(),
callout_active() and callout_deactivate() macros can be used to
achieve simpler race-free callout semantics in many situations.
callout_stop(), except that if the callout being stopped is currently
in progress, it blocks attempts to reset the callout and waits until the
callout is completed before it returns.
This makes it possible to clean up callout-using code safely, e.g.,
without potentially freeing memory which is still being used by a callout.
Reviewed by: mux, gallatin, rwatson, jhb
callout lock while the callout is happening. So the serialization
that I thought was happening isn't. Therefore, remove the part of the
bugs that says this. Leave in the other bug as it is very hard to
work around (impossible?).
Fix various typos.
Also note that timeout/untimeout are considered to be the old interface and
the callout interface should be used insetad.
Submitted by: bde (first two) and wollman (third)
callout has finished or is in progress. Also document that the
locking of the callout code for FreeBSD 5 has eliminated the 'or is in
progress' clause as a possibility and that such elimination is an
accident of the implementation and shouldn't be relied upon.
cd src/share; find man[1-9] -type f|xargs perl -pi -e 's/[ \t]+$//'
BTW, what editors are the culprits? I'm using vim and it shows
me whitespace at EOL in troff files with a thick blue block...
Reviewed by: Silence from cvs diff -b
MFC after: 7 days
spl0) and some bitrot (the not-so-new callout_init/stop/reset functions
were not mentioned; the callout_activate/deactivate/pending macros are
still not mentioned).
Submitted by: mostly by jlemon
This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
