same time as it is changed back into a normal file. The locker would
get the shared "snaplk" lock which would no longer be the correct lock
for the vnode.
This does not do what I wanted as all dirty buffers must be flushed
by the call to ffs_sync and any remaining dependency work would mean
that this failed.
Pointed out by: tegge
Fix detection of active unlinked files by checking VI_OWEINACT and
VI_DOINGINACT in addition to v_usecount.
Defer inactive handling for unlinked files if the file system is mostly
suspended (secondary writes being blocked).
Perform deferred inactive handling after the file system is resumed.
has many positive effects including improved smp locking, reducing
interdependencies between mounts that can lead to deadlocks, etc.
- Add the softdep worklist and various counters to the ufsmnt structure.
- Add a mount pointer to the workitem and remove mount pointers from the
various structures derived from the workitem as they are now redundant.
- Remove the poor-man's semaphore protecting softdep_process_worklist and
softdep_flushworklist. Several threads may now process the list
simultaneously.
- Add softdep_waitidle() to block the thread until all pending
dependencies being operated on by other threads have been flushed.
- Use softdep_waitidle() in unmount and snapshots to block either
operation until the fs is stable.
- Remove softdep worklist processing from the syncer and move it into the
softdep_flush() thread. This thread processes all softdep mounts
once each second and when it is called via the new softdep_speedup()
when there is a resource shortage. This removes the softdep hook
from the kernel and various hacks in header files to support it.
Reviewed by/Discussed with: tegge, truckman, mckusick
Tested by: kris
that NetBSD implemented it independently of them (don't know which one
was actually first). This saves about 24k for those times you don't
need snapshot support (like when running off a ram disk, or in an
embedded environment where size matters).
updated by a process holding the snapshot lock. Another process updating a
different inode in the same inodeblock will do copy on write checks and lock in
the opposite direction.
The snapshot code force a copy on write of these blocks manually (cf. start of
expunge_ufs[12]) and these inode blocks are later put on snapblklist.
This partial fix is to 'drain' the relevant ffs_copyonwrite() operation after
installing new snapblklist. This is not a 100% solution since a failed block
allocation can cause implicit fsync() which might deadlock before the new
snapblklist has been installed.
file is flushed by a process not holding snaplk (e.g. bufdaemon). Another
process might hold snaplk and try to access the block due to ffs_copyonwrite
processing.
the cg map buffer being held when writing indirect blocks. The process ends up
in ffs_copyonwrite(), attempting to get snaplk while holding the cg map buffer
lock.
Another process might be in ffs_copyonwrite(), trying to allocate a new block
for a copy. It would hold snaplk while trying to get the cg map buffer lock.
Release the cg map buffer early and use the copy for most of the cgaccount
processing to avoid this deadlock.
skipping the call from ffs_snapremove() if the block number is zero.
Simplify snapshot locking in ffs_copyonwrite() and ffs_snapblkfree() by using
the same locking protocol for low block numbers as for larger block numbers.
This removes a lock leak that could happen if vn_lock() succeeded after
lockmgr() failed in ffs_snapblkfree().
Check if snapshot is gone before retrying a lock in ffs_copyonwrite().
Add a new private thread flag to indicate that the thread should
not sleep if runningbufspace is too large.
Set this flag on the bufdaemon and syncer threads so that they skip
the waitrunningbufspace() call in bufwrite() rather than than
checking the proc pointer vs. the known proc pointers for these two
threads. A way of preventing these threads from being starved for
I/O but still placing limits on their outstanding I/O would be
desirable.
Set this flag in ffs_copyonwrite() to prevent bufwrite() calls from
blocking on the runningbufspace check while holding snaplk. This
prevents snaplk from being held for an arbitrarily long period of
time if runningbufspace is high and greatly reduces the contention
for snaplk. The disadvantage is that ffs_copyonwrite() can start
a large amount of I/O if there are a large number of snapshots,
which could cause a deadlock in other parts of the code.
Call runningbufwakeup() in ffs_copyonwrite() to decrement runningbufspace
before attempting to grab snaplk so that I/O requests waiting on
snaplk are not counted in runningbufspace as being in-progress.
Increment runningbufspace again before actually launching the
original I/O request.
Prior to the above two changes, the system could deadlock if enough
I/O requests were blocked by snaplk to prevent runningbufspace from
falling below lorunningspace and one of the bawrite() calls in
ffs_copyonwrite() blocked in waitrunningbufspace() while holding
snaplk.
See <http://www.holm.cc/stress/log/cons143.html>
- Don't intermingle direct calls to lockmgr and indirect calls through
VOPs. This will be important in the future.
- Dont lock the devvp's interlock just to release it on the next line by
passing LK_INTERLOCK to lockmgr.
- Restructure ffs_snapshot_unmount so we don't call free() with the
devvp's interlock locked.
The "business class upgrade" was implemented in UFS's VOP_LOCK
implementation ufs_lock() which is the wrong layer, so move it to
ffs_lock().
Also, as long as we have not abandonned advanced vfs-stacking we
should not preclude it from happening: instead of implementing a
copy locally, use the VOP_LOCK_APV(&ufs) to correctly arrive at
vop_stdlock() at the bottom.
I'm not sure why a credential was added to these in the first place, it is
not used anywhere and it doesn't make much sense:
The credentials for syncing a file (ability to write to the
file) should be checked at the system call level.
Credentials for syncing one or more filesystems ("none")
should be checked at the system call level as well.
If the filesystem implementation needs a particular credential
to carry out the syncing it would logically have to the
cached mount credential, or a credential cached along with
any delayed write data.
Discussed with: rwatson
prematurely report that they were full and/or to panic the kernel
with the message ``ffs_clusteralloc: allocated out of group''.
Submitted by: Henry Whincup <henry@jot.to>
MFC after: 1 week
This eliminates a bunch of vnode overhead (approx 1-2 % speed
improvement) and gives us more control over the access to the storage
device.
Access counts on the underlying device are not correctly tracked and
therefore it is possible to read-only mount the same disk device multiple
times:
syv# mount -p
/dev/md0 /var ufs rw 2 2
/dev/ad0 /mnt ufs ro 1 1
/dev/ad0 /mnt2 ufs ro 1 1
/dev/ad0 /mnt3 ufs ro 1 1
Since UFS/FFS is not a synchrousely consistent filesystem (ie: it caches
things in RAM) this is not possible with read-write mounts, and the system
will correctly reject this.
Details:
Add a geom consumer and a bufobj pointer to ufsmount.
Eliminate the vnode argument from softdep_disk_prewrite().
Pick the vnode out of bp->b_vp for now. Eventually we
should find it through bp->b_bufobj->b_private.
In the mountcode, use g_vfs_open() once we have used
VOP_ACCESS() to check permissions.
When upgrading and downgrading between r/o and r/w do the
right thing with GEOM access counts. Remove all the
workarounds for not being able to do this with VOP_OPEN().
If we are the root mount, drop the exclusive access count
until we upgrade to r/w. This allows fsck of the root
filesystem and the MNT_RELOAD to work correctly.
Set bo_private to the GEOM consumer on the device bufobj.
Change the ffs_ops->strategy function to call g_vfs_strategy()
In ufs_strategy() directly call the strategy on the disk
bufobj. Same in rawread.
In ffs_fsync() we will no longer see VCHR device nodes, so
remove code which synced the filesystem mounted on it, in
case we came there. I'm not sure this code made sense in
the first place since we would have taken the specfs route
on such a vnode.
Redo the highly bogus readblock() function in the snapshot
code to something slightly less bogus: Constructing an uio
and using physio was really quite a detour. Instead just
fill in a bio and ship it down.
is ffs_copyonwrite() and the only place it can be called from is FFS which
would never want to call another filesystems copyonwrite method, should one
exist, so there is no reason why anything generic should know about this.
and the previously malloc'ed snapshot lock.
Malloc struct snapdata instead of just the lock.
Replace snapshot fields in cdev with pointer to snapdata (saves 16 bytes).
While here, give the private readblock() function a vnode argument
in preparation for moving UFS to access GEOM directly.
our cached 'next vnode' being removed from this mountpoint. If we
find that it was recycled, we restart our traversal from the start
of the list.
Code to do that is in all local disk filesystems (and a few other
places) and looks roughly like this:
MNT_ILOCK(mp);
loop:
for (vp = TAILQ_FIRST(&mp...);
(vp = nvp) != NULL;
nvp = TAILQ_NEXT(vp,...)) {
if (vp->v_mount != mp)
goto loop;
MNT_IUNLOCK(mp);
...
MNT_ILOCK(mp);
}
MNT_IUNLOCK(mp);
The code which takes vnodes off a mountpoint looks like this:
MNT_ILOCK(vp->v_mount);
...
TAILQ_REMOVE(&vp->v_mount->mnt_nvnodelist, vp, v_nmntvnodes);
...
MNT_IUNLOCK(vp->v_mount);
...
vp->v_mount = something;
(Take a moment and try to spot the locking error before you read on.)
On a SMP system, one CPU could have removed nvp from our mountlist
but not yet gotten to assign a new value to vp->v_mount while another
CPU simultaneously get to the top of the traversal loop where it
finds that (vp->v_mount != mp) is not true despite the fact that
the vnode has indeed been removed from our mountpoint.
Fix:
Introduce the macro MNT_VNODE_FOREACH() to traverse the list of
vnodes on a mountpoint while taking into account that vnodes may
be removed from the list as we go. This saves approx 65 lines of
duplicated code.
Split the insmntque() which potentially moves a vnode from one mount
point to another into delmntque() and insmntque() which does just
what the names say.
Fix delmntque() to set vp->v_mount to NULL while holding the
mountpoint lock.
Move diagnostic printf after vget. This might delay the debug
output some, but at least it keeps kernel from exploding if
DEBUG_VFS_LOCKS is in effect.
Introduce two new macros MNT_ILOCK(mp)/MNT_IUNLOCK(mp) to
operate on this mutex transparently.
Eventually new mutex will be protecting more fields in
struct mount, not only vnode list.
Discussed with: jeff
