cvs commit: src/sys/kern vfs_subr.c

[Jeff Roberson]

jeff        2005-06-16 04:41:42 UTC

  FreeBSD src repository

  Modified files:
    sys/kern             vfs_subr.c 
  Log:
   - Change holdcnt use around vnode recycling.  We now always keep a holdcnt
     ref while we're calling vgone().  This prevents transient refs from
     re-adding us to the free list.  Previously, a vfree() triggered via
     vinvalbuf() getting rid of all of a vnode's pages could place a partially
     destructed vnode on the free list where vtryrecycle() could find it.  The
     first call to vtryrecycle would hang up on the vnode lock, but when it
     failed it would place a now dead vnode onto the free list, and another
     call to vtryrecycle() would free an already free vnode.  There were many
     complications of having a zero ref count while freeing which can now go
     away.
   - Change vdropl() to release the interlock before returning.  All callers
     now respect this, so vdropl() directly frees VI_DOOMED vnodes once the
     last ref is dropped.  This means that we'll never have VI_DOOMED vnodes
     on the free list.
   - Seperate v_incr_usecount() into v_incr_usecount(), v_decr_usecount() and
     v_decr_useonly().  The incr/decr split is so that incr usecount can
     return with the interlock still held while decr drops the interlock so
     it can call vdropl() which will potentially free the vnode.  The calling
     function can't drop the lock of an already free'd node.  v_decr_useonly()
     drops a usecount without droping the hold count.  This is done so the
     usecount reaches zero in vput() before we recycle, however the holdcount
     is still 1 which prevents any new references from placing the vnode
     back on the free list.
   - Fix vnlrureclaim() to vhold the vnode since it doesn't do a vget().  We
     wouldn't want vnlrureclaim() to bump the usecount since this has
     different semantics.  Also change vnlrureclaim() to do a NOWAIT on the
     vn_lock.  When this function runs we're usually in a desperate situation
     and we wouldn't want to wait for any specific vnode to be released.
   - Fix a bunch of misc comments to reflect the new behavior.
   - Add vhold() and vdrop() to vflush() for the same reasons that we do in
     vlrureclaim().  Previously we held no reference and a vnode could have
     been freed while we were waiting on the lock.
   - Get rid of vlruvp() and vfreehead().  Neither are used.  vlruvp() should
     really be rethought before it's reintroduced.
   - vgonel() always returns with the vnode locked now and never puts the
     vnode back on a free list.  The vnode will be freed as soon as the last
     reference is released.
  
  Sponsored by:   Isilon Systems, Inc.
  Debugging help from:    Kris Kennaway, Peter Holm
  Approved by:    re (blanket vfs)
  
  Revision  Changes    Path
  1.632     +198 -202  src/sys/kern/vfs_subr.c