cvs commit: src/sys/kern kern_lock.c src/sys/sys lockmgr.h
attilio at FreeBSD.org
Tue Feb 5 16:37:15 PST 2008
attilio 2008-02-06 00:37:14 UTC
FreeBSD src repository
Add WITNESS support to lockmgr locking primitive.
This support tries to be as parallel as possible with other locking
primitives, but there are differences; more specifically:
- The base witness support is alredy equipped for allowing lock
duplication acquisition as lockmgr rely on this.
- In the case of lockmgr_disown() the lock result unlocked by witness
even if it is still held by the "kernel context"
- In the case of upgrading we can have 3 different situations:
* Total unlocking of the shared lock and nothing else
* Real witness upgrade if the owner is the first upgrader
* Shared unlocking and exclusive locking if the owner is not the first
upgrade but it is still allowed to upgrade
- LK_DRAIN is basically handled like an exclusive acquisition
Additively new options LK_NODUP and LK_NOWITNESS can now be used with
lockinit(): LK_NOWITNESS disables WITNESS for the specified lock while
LK_NODUP enable duplicated locks tracking. This will require manpages
update and a __FreeBSD_version bumping (addressed by further commits).
This patch also fixes a problem occurring if a lockmgr is held in
exclusive mode and the same owner try to acquire it in shared mode:
currently there is a spourious shared locking acquisition while what
we really want is a lock downgrade. Probabilly, this situation can be
better served with a EDEADLK failing errno return.
Side note: first testing on this patch alredy reveleated several LORs
reported, so please expect LORs cascades until resolved. NTFS also is
reported broken by WITNESS introduction. BTW, NTFS is exposing a lock
leak which needs to be fixed, and this patch can help it out if
Tested by: kris, yar, Scot Hetzel <swhetzel at gmail dot com>
Revision Changes Path
1.121 +46 -11 src/sys/kern/kern_lock.c
1.59 +5 -1 src/sys/sys/lockmgr.h
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