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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)
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