2000-11-04 10:01:08 +00:00
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Copyright 2000, International Business Machines Corporation and others.
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All Rights Reserved.
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This software has been released under the terms of the IBM Public
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License. For details, see the LICENSE file in the top-level source
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directory or online at http://www.openafs.org/dl/license10.html
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2000-11-04 02:13:13 +00:00
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Locking order (in order of locking) --
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1. PVN lock in cache entry. Locks out pvn operations on vnode from
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our own layer.
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2. VCache entries. Multiple ones can be locked, in which case
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they're locked in order of vnode within the same volume. afs_AccessOK
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is called before locking other entries.
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3. afs_xvcache locked before afs_xdcache in afs_remove, afs_symlink, etc
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in the file afs_vnodeops.c
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4. afs_xvcache. Must be able to load new cache
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entries while holding locks on others. Note this means you can't lock
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a cache entry while holding either of this lock, unless, as in afs_create,
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the cache entry is actually created while the afs_xvcache is held.
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5. afs_xvcb. Volume callback lock. Locked before afs_xserver in afs_RemoveVCB.
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6. afs_xvolume -- allows low-level server etc stuff to happen while
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creating a volume?
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7. afs_xuser -- afs_xuser locked before afs_xserver and afs_xconn in
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PUnlog.
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8. afs_xcell -- locked before server in afs_GetCell.
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9. afs_xserver -- afs_xserver locked before afs_xconn in
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afs_ResetUserConns.
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10. afs_xsrvAddr -- afs_xserver locked before afs_xsrvAddr in
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afs_CheckServers.
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11. afs_xconn -- see above
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12. Individual volume locks. Must be after afs_xvolume so we can
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iterate over all volumes without others being inserted/deleted. Same
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hack doesn't work for cache entry locks since we need to be able to
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lock multiple cache entries (but not multiple volumes) simultaneously.
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13. afs_xdnlc -- locked after afs_xvcache in afs_osidnlc.c. Shouldn't
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interact with any of the other locks.
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14. afs_xcbhash -- No code which holds xcbhash (all of it is in
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afs_cbqueue.c) attempts to get any other locks, so it should always be
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obtained last. It is locked in afs_DequeueCallbacks which is called from
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afs_FlushVCache with afs_xvcache write-locked.
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***** RX_ENABLE_LOCKS
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Many fine grained locks are used by Rx on the AIX4.1 platform. These
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need to be explained.
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It is likely they could be used preference to the afs_rxglobal_lock on
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AFS_GLOBAL_SUNLOCK platforms.
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***** GLOBAL LOCKS
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98. afs_global_lock -- This lock provides a non-preemptive environment
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for the bulk of the AFS kernel code on platforms that require it.
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Presently this includes SunOS5 and SGI53 systems. This lock is dropped
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and reaquired frequently, especially around calls back to the OS that
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may reenter AFS such as vn_rele.
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Generally, this lock should not be used to explicitly avoid locking
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data structures that need synchronization. However, much existing code
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is deficient in this regard (e.g. afs_getevent).
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99. afs_rxglobal_lock -- This lock is obtained after the afs_global_lock
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at process level but is obtained independently during packet arrival
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"interrupts" and during fasttimo processing.
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***** OS LOCKS
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100. The vnode lock on SunOS and SGI53 protects the its reference count.
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101. NETPRI/USERPRI -- These are not really locks but provide mutual
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exclusion against packet and timer interrupts.
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