git: HAMMER VFS - Major retooling of the refcount mechanics, and
commit 250aec18e447d7c9db30d4f905d21333e825a9d9
Author: Matthew Dillon <dillon@apollo.backplane.com>
Date: Mon Mar 15 02:07:23 2010 -0700
HAMMER VFS - Major retooling of the refcount mechanics, and fix a deadlock
* Add an interlock to hammer_lock->refs which is independent of
hammer_lock->lockval.
* Retool the refcount mechanics to integrate the interlock on 0->1 and
1->0 transitions.
In addition implement a check bit to deal with serialization races
between threads which forces all threads to interlock. This deals
with the case where one thread bumps the refcount (lock->refs) but
is unable to immediateliy acquire the interlock. Other threads doing
the same thing will race and lock->refs will be bumped far higher
than 1. The check bit is set on the 0->1 transition and enforces
all threads to serialize until one (usually the first to acquire the
lock) is able to dispose of the check condition.
The transition interlocks are used to do I/O loading and validation
on the 0->N transition and I/O unloading and invalidation on the 1->0
transition.
* The new integrated mechanics also simplify hammer_io's handling of
B_LOCKED slightly and properly interlocks changes in disposition for
the related buffer cache buffer against refcount transitions.
* The new integrated refcount/interlock is also more optimal as the
combined operation can be done in a single atomic_cmpset_int() call,
and fully MPSAFE. Even though other major portions of HAMMER are not
yet MPSAFE getting this particular bit dealt with will ease MP work
later on.
* Retool the volume, buffer, and node referencing code to use the new
mechanics. This fixes a deadlock. These routines were previously
acquiring an exclusive lock instead of an interlock. The exclusive
lock could combine with shared locks held by the same thread to create
a deadlock situation against other threads.
Use of the interlock fixes this particular deadlock.
Reported-by: Francois Tigeot <ftigeot@wolfpond.org> (deadlock report)
Summary of changes:
sys/vfs/hammer/hammer.h | 62 ++++-
sys/vfs/hammer/hammer_btree.c | 6 +-
sys/vfs/hammer/hammer_flusher.c | 8 -
sys/vfs/hammer/hammer_inode.c | 30 ++--
sys/vfs/hammer/hammer_io.c | 47 +++--
sys/vfs/hammer/hammer_object.c | 6 +-
sys/vfs/hammer/hammer_ondisk.c | 454 ++++++++++++++++++++++----------------
sys/vfs/hammer/hammer_recover.c | 10 +-
sys/vfs/hammer/hammer_subs.c | 462 ++++++++++++++++++++++++++++++++++++---
9 files changed, 803 insertions(+), 282 deletions(-)
http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/250aec18e447d7c9db30d4f905d21333e825a9d9
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