not in the namecache when shared lookups are enabled (vfs.lookup_shared=1,
it is currently off by default) and the filesystem supports shared lookups
(e.g. NFS client). Specifically, if multiple concurrent LOOKUPs both miss
in the name cache in parallel, each of the lookups may each end up adding an
entry to the namecache resulting in duplicate entries in the namecache
for the same pathname. A subsequent removal of the mapping of that
pathname to that vnode (via remove or rename) would only evict one of the
entries from the name cache. As a result, subseqent lookups for that
pathname would still return the old vnode.
This race was observed with shared lookups over NFS where a file was updated
by writing a new file out to a temporary file name and then renaming that
temporary file to the "real" file to effect atomic updates of a file. Other
processes on the same client that were periodically reading the file would
occasionally receive an ESTALE error from open(2) because the VOP_GETATTR()
in nfs_open() would receive that error when given the stale vnode.
The fix here is to check for duplicates in cache_enter() and just return
if an entry for this same directory and leaf file name for this vnode is
already in the cache. The check for duplicates is done by walking the
per-vnode list of name cache entries. It is expected that this list should
be very small in the common case (usually 0 or 1 entries during a
cache_enter() since most files only have 1 "leaf" name).
Reviewed by: ups, scottl
MFC after: 2 months
processes are not producing absolute pathname tokens. It is required
that audited pathnames are generated relative to the global root mount
point. This modification changes our implementation of audit_canon_path(9)
and introduces a new function: vn_fullpath_global(9) which performs a
vnode -> pathname translation relative to the global mount point based
on the contents of the name cache. Much like vn_fullpath,
vn_fullpath_global is a wrapper function which called vn_fullpath1.
Further, the string parsing routines have been converted to use the
sbuf(9) framework. This change also removes the conditional acquisition
of Giant, since the vn_fullpath1 method will not dip into file system
dependent code.
The vnode locking was modified to use vhold()/vdrop() instead the vref()
and vrele(). This will modify the hold count instead of modifying the
user count. This makes more sense since it's the kernel that requires
the reference to the vnode. This also makes sure that the vnode does not
get recycled we hold the reference to it. [1]
Discussed with: rwatson
Reviewed by: kib [1]
MFC after: 2 weeks
no longer needed, but for now we still want to be consistent with other
similar checks in the tree.
- Call ASSERT_VOP_ELOCKED() only when vget() returns 0.
Reviewed by: jeff
after each SYSINIT() macro invocation. This makes a number of
lightweight C parsers much happier with the FreeBSD kernel
source, including cflow's prcc and lxr.
MFC after: 1 month
Discussed with: imp, rink
always curthread.
As KPI gets broken by this patch, manpages and __FreeBSD_version will be
updated by further commits.
Tested by: Andrea Barberio <insomniac at slackware dot it>
conjuction with 'thread' argument passing which is always curthread.
Remove the unuseful extra-argument and pass explicitly curthread to lower
layer functions, when necessary.
KPI results broken by this change, which should affect several ports, so
version bumping and manpage update will be further committed.
Tested by: kris, pho, Diego Sardina <siarodx at gmail dot com>
Remove this argument and pass curthread directly to underlying
VOP_LOCK1() VFS method. This modify makes the code cleaner and in
particular remove an annoying dependence helping next lockmgr() cleanup.
KPI results, obviously, changed.
Manpage and FreeBSD_version will be updated through further commits.
As a side note, would be valuable to say that next commits will address
a similar cleanup about VFS methods, in particular vop_lock1 and
vop_unlock.
Tested by: Diego Sardina <siarodx at gmail dot com>,
Andrea Di Pasquale <whyx dot it at gmail dot com>
parent vnode and relock it after locking child vnode. The problem was that
we always relock it exclusively, even when it was share-locked.
Discussed with: jeff
and flags with an sxlock. This leads to a significant and measurable
performance improvement as a result of access to shared locking for
frequent lookup operations, reduced general overhead, and reduced overhead
in the event of contention. All of these are imported for threaded
applications where simultaneous access to a shared file descriptor array
occurs frequently. Kris has reported 2x-4x transaction rate improvements
on 8-core MySQL benchmarks; smaller improvements can be expected for many
workloads as a result of reduced overhead.
- Generally eliminate the distinction between "fast" and regular
acquisisition of the filedesc lock; the plan is that they will now all
be fast. Change all locking instances to either shared or exclusive
locks.
- Correct a bug (pointed out by kib) in fdfree() where previously msleep()
was called without the mutex held; sx_sleep() is now always called with
the sxlock held exclusively.
- Universally hold the struct file lock over changes to struct file,
rather than the filedesc lock or no lock. Always update the f_ops
field last. A further memory barrier is required here in the future
(discussed with jhb).
- Improve locking and reference management in linux_at(), which fails to
properly acquire vnode references before using vnode pointers. Annotate
improper use of vn_fullpath(), which will be replaced at a future date.
In fcntl(), we conservatively acquire an exclusive lock, even though in
some cases a shared lock may be sufficient, which should be revisited.
The dropping of the filedesc lock in fdgrowtable() is no longer required
as the sxlock can be held over the sleep operation; we should consider
removing that (pointed out by attilio).
Tested by: kris
Discussed with: jhb, kris, attilio, jeff
- Remove also "MP SAFE" after prior "MPSAFE" pass. (suggested by bde)
- Remove extra blank lines in some cases.
- Add extra blank lines in some cases.
- Remove no-op comments consisting solely of the function name, the word
"syscall", or the system call name.
- Add punctuation.
- Re-wrap some comments.
filesystem agnostic. We are not touching any file system specific functions
in this code path. Since we have a cache lock, there is really no need to
keep Giant around here.
This eliminates Giant acquisitions for any syscall which is auditing pathnames.
Discussed with: jeff
cache_zap() to clear the v_dd pointers when a directory vnode is forcibly
discarded. For this to work, all vnodes with v_dd pointers to a directory
must also have name cache entries linked via v_cache_dst to that dvp
otherwise we could not find them at cache_purge() time. The following
code snipit could break this guarantee by unlinking a directory before
fetching it's dotdot. The dotdot lookup would initialize the v_dd field
of the unlinked directory which could never be cleared. To fix this
we don't initialize v_dd for orphaned vnodes.
printf("rmdir: %d\n", rmdir("../foo")); /* foo is cwd */
printf("chdir: %d\n", chdir(".."));
printf("%s\n", getwd(NULL));
Sponsored by: Isilon Systems, Inc.
Discovered by: kkenn
Approved by: re (blanket vfs)
vnodes whose names it caches, so we no longer need a `generation
number' to tell us if a referenced vnode is invalid. Replace the use
of the parent's v_id in the hash function with the address of the
parent vnode.
Tested by: Peter Holm
Glanced at by: jeff, phk
except for places where people forget to update one of them. We now
collect only one set of stats for both of these routines. Other
changes in this commit include:
- Start acquiring Giant again in vn_fullpath(), since it is required
when crossing a mount point.
- Expand the scope of the cache lock to avoid dropping it and
picking it up again for every pathname component. This also
makes it trivial to avoid races in stats collection.
- Assert that nc_dvp == v_dd for directories instead of returning
an error to userland when this is not true. AFAIK, it should
always be true when v_dd is non-null.
- For vn_fullpath(), handle the first (non-directory) vnode
separately.
Glanced at by: jeff, phk
to cache_lookup(). This allows us to acquire the vnode interlock before
dropping the cache lock. This protects the vnodes identity until we
have locked it.
Sponsored by: Isilon Systems, Inc.
config option have now been fixed. All filesystems are properly locked
and checked via DEBUG_VFS_LOCKS. Remove the workaround code.
Sponsored by: Isilon Systems, Inc.
vnode lock is much simpler than I originally thought it would be.
Now, the cache lock is always acquired before the vnode lock.
- Provide some gotos in __getcwd() to simplify the unlocking a bit.
- Move Giant acquisition down into __getcwd().
Sponsored By: Isilon Systems, Inc.
small but noticeable increase in performance for name lookup operations.
The code uses two zones, one for short names (less than 32 characters)
and one for long names (up to NAME_MAX). Since most file names are
fairly short, this saves a considerable amount of space that would
otherwise be wasted if we always allocated NAME_MAX bytes. The cutoff
value of 32 characters was picked arbitrarily and may benefit from some
tweaking; it could also be made into a tunable.
Submitted by: hmp
but I decided that it was important for this patch to not bit-rot, and
since it is mainly moving code around, the total amount of entropy is
epsilon /phk)
This is a patch to move the common parts of linux_getcwd() back into
kern/vfs_cache.c so that the standard FreeBSD libc getcwd() can use it's
extended functionality. The linux syscall linux_getcwd() in
compat/linux/linux_getcwd.c has been rewritten to use it too. It should
be possible to simplify libc's getcwd() after this. No doubt this code
needs some cleaning up, since I've left in the sysctl variables I used
for debugging.
PR: 48169
Submitted by: James Whitwell <abacau@yahoo.com.au>
