Date: Tue, 31 Dec 2002 11:38:04 -0800 (PST) From: Alan Cox <alc@FreeBSD.org> To: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/vm vm_map.c vm_map.h Message-ID: <200212311938.gBVJc43Y039211@repoman.freebsd.org>
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alc 2002/12/31 11:38:04 PST
Modified files:
sys/vm vm_map.c vm_map.h
Log:
Implement a variant locking scheme for vm maps: Access to system maps
is now synchronized by a mutex, whereas access to user maps is still
synchronized by a lockmgr()-based lock. Why? No single type of lock,
including sx locks, meets the requirements of both types of vm map.
Sometimes we sleep while holding the lock on a user map. Thus, a
a mutex isn't appropriate. On the other hand, both lockmgr()-based
and sx locks release Giant when a thread/process blocks during
contention for a lock. This could lead to a race condition in a legacy
driver (that relies on Giant for synchronization) if it attempts to
kmem_malloc() and fails to immediately obtain the lock. Fortunately,
we never sleep while holding a system map lock.
Revision Changes Path
1.278 +38 -16 src/sys/vm/vm_map.c
1.94 +1 -0 src/sys/vm/vm_map.h
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