so make the code slightly more uniform. The vnode lock is acquired in
all cases and now the only difference between VCHR and other is we
call UFS_UPDATE instead of VOP_FSYNC().
Use pre-emption detection to avoid the need for wiring a userland buffer
when copying opaque data structures.
sysctl_wire_old_buffer() is now a no-op. Other consumers of this
API should use pre-emption detection to notice update collisions.
vslock() and vsunlock() should no longer be called by any code
and should be retired in subsequent commits.
Discussed with: pete, phk
MFC after: 1 week
go away in due course. Involuntary pre-emption means that we can't count
on wiring of pages alone for consistency when performing a SYSCTL_OUT()
bigger than PAGE_SIZE.
Discussed with: pete, phk
- Slightly rewrite the fsync loop to be more lock friendly. We must
acquire the vnode interlock before dropping the mnt lock. We must
also check XLOCK to prevent vclean() races.
- Use LK_INTERLOCK in the vget() in ffs_sync to further prevent vclean()
races.
- Use a local variable to store the results of the nvp == TAILQ_NEXT
test so that we do not access the vp after we've vrele()d it.
- Add an XXX comment about UFS_UPDATE() not being protected by any lock
here. I suspect that it should need the VOP lock.
LK_RETRY either, we don't want this vnode if it turns into another.
- Remove the code that checks the mount point after acquiring the lock
we are guaranteed to either fail or get the vnode that we wanted.
- In vtryrecycle() try to vgonel the vnode if all of the previous checks
passed. We won't vgonel if someone has either acquired a hold or usecount
or started the vgone process elsewhere. This is because we may have been
removed from the free list while we were inspecting the vnode for
recycling.
- The VI_TRYLOCK stops two threads from entering getnewvnode() and recycling
the same vnode. To further reduce the likelyhood of this event, requeue
the vnode on the tail of the list prior to calling vtryrecycle(). We can
not actually remove the vnode from the list until we know that it's
going to be recycled because other interlock holders may see the VI_FREE
flag and try to remove it from the free list.
- Kill a bogus XXX comment. If XLOCK is set we shouldn't wait for it
regardless of MNT_WAIT because the vnode does not actually belong to
this filesystem.
purge, the purge in vclean, and the filesystems purge, we had 3 purges
per vnode.
- Move the insmntque(vp, 0) to vclean() so that we may remove it from the
two vgone() functions and reduce the number of lock operations required.
whether or not the sync failed. This could potentially get set between
the time that we VOP_UNLOCK and VI_LOCK() but the race would harmelssly
lead to the sync being delayed by an extra 30 seconds. If we do not move
the vnode it could cause an endless loop if it continues to fail to sync.
- Use vhold and vdrop to stop the vnode from changing identities while we
have it unlocked. Other internal vfs lists are likely to follow this
scheme.
- Create a new function, vgonechrl(), which performs vgone for an in-use
character device. Move the code from vflush() that did this into
vgonechrl().
- Hold the xlock across the entirety of vgonel() and vgonechrl() so that
at no point will an invalid vnode exist on any list without XLOCK set.
- Move the xlock code out of vclean() now that it is in the vgone*()
functions.
work in, but we had it mapped read-only. While this has always been the
case, the PG_PS enable hack hid it and the apm bios code ended up taking
advantage of it.
