linux.git/fs/dcache.c, branch v2.6.38

fs/dcache: allow d_obtain_alias() to return unhashed dentries

2011-03-10T10:18:54+00:00

Without this patch, inodes are not promptly freed on last close of an
unlinked file by an nfs client:

	client$ mount -tnfs4 server:/export/ /mnt/
	client$ tail -f /mnt/FOO
	...
	server$ df -i /export
	server$ rm /export/FOO
	(^C the tail -f)
	server$ df -i /export
	server$ echo 2 >/proc/sys/vm/drop_caches
	server$ df -i /export

the df's will show that the inode is not freed on the filesystem until
the last step, when it could have been freed after killing the client's
tail -f. On-disk data won't be deallocated either, leading to possible
spurious ENOSPC.

This occurs because when the client does the close, it arrives in a
compound with a putfh and a close, processed like:

	- putfh: look up the filehandle.  The only alias found for the
	  inode will be DCACHE_UNHASHED alias referenced by the filp
	  this, so it creates a new DCACHE_DISCONECTED dentry and
	  returns that instead.
	- close: closes the existing filp, which is destroyed
	  immediately by dput() since it's DCACHE_UNHASHED.
	- end of the compound: release the reference
	  to the current filehandle, and dput() the new
	  DCACHE_DISCONECTED dentry, which gets put on the
	  unused list instead of being destroyed immediately.

Nick Piggin suggested fixing this by allowing d_obtain_alias to return
the unhashed dentry that is referenced by the filp, instead of making it
create a new dentry.

Leave __d_find_alias() alone to avoid changing behavior of other
callers.

Also nfsd doesn't need all the checks of __d_find_alias(); any dentry,
hashed or unhashed, disconnected or not, should work.

Signed-off-by: J. Bruce Fields 
Signed-off-by: Al Viro

fs: fix new dcache.c kernel-doc warnings

2011-01-23T04:32:38+00:00

Fix new fs/dcache.c kernel-doc warnings:

  Warning(fs/dcache.c:184): No description found for parameter 'dentry'
  Warning(fs/dcache.c:296): No description found for parameter 'parent'
  Warning(fs/dcache.c:1985): No description found for parameter 'dparent'
  Warning(fs/dcache.c:1985): Excess function parameter 'parent' description in 'd_validate'

Signed-off-by: Randy Dunlap 
Cc:	Alexander Viro 
Cc:	Nick Piggin 
Signed-off-by: Linus Torvalds

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6

2011-01-16T19:31:50+00:00

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6: (23 commits)
  sanitize vfsmount refcounting changes
  fix old umount_tree() breakage
  autofs4: Merge the remaining dentry ops tables
  Unexport do_add_mount() and add in follow_automount(), not ->d_automount()
  Allow d_manage() to be used in RCU-walk mode
  Remove a further kludge from __do_follow_link()
  autofs4: Bump version
  autofs4: Add v4 pseudo direct mount support
  autofs4: Fix wait validation
  autofs4: Clean up autofs4_free_ino()
  autofs4: Clean up dentry operations
  autofs4: Clean up inode operations
  autofs4: Remove unused code
  autofs4: Add d_manage() dentry operation
  autofs4: Add d_automount() dentry operation
  Remove the automount through follow_link() kludge code from pathwalk
  CIFS: Use d_automount() rather than abusing follow_link()
  NFS: Use d_automount() rather than abusing follow_link()
  AFS: Use d_automount() rather than abusing follow_link()
  Add an AT_NO_AUTOMOUNT flag to suppress terminal automount
  ...

Add a dentry op to handle automounting rather than abusing follow_link()

2011-01-16T01:05:03+00:00

Add a dentry op (d_automount) to handle automounting directories rather than
abusing the follow_link() inode operation.  The operation is keyed off a new
dentry flag (DCACHE_NEED_AUTOMOUNT).

This also makes it easier to add an AT_ flag to suppress terminal segment
automount during pathwalk and removes the need for the kludge code in the
pathwalk algorithm to handle directories with follow_link() semantics.

The ->d_automount() dentry operation:

	struct vfsmount *(*d_automount)(struct path *mountpoint);

takes a pointer to the directory to be mounted upon, which is expected to
provide sufficient data to determine what should be mounted.  If successful, it
should return the vfsmount struct it creates (which it should also have added
to the namespace using do_add_mount() or similar).  If there's a collision with
another automount attempt, NULL should be returned.  If the directory specified
by the parameter should be used directly rather than being mounted upon,
-EISDIR should be returned.  In any other case, an error code should be
returned.

The ->d_automount() operation is called with no locks held and may sleep.  At
this point the pathwalk algorithm will be in ref-walk mode.

Within fs/namei.c itself, a new pathwalk subroutine (follow_automount()) is
added to handle mountpoints.  It will return -EREMOTE if the automount flag was
set, but no d_automount() op was supplied, -ELOOP if we've encountered too many
symlinks or mountpoints, -EISDIR if the walk point should be used without
mounting and 0 if successful.  The path will be updated to point to the mounted
filesystem if a successful automount took place.

__follow_mount() is replaced by follow_managed() which is more generic
(especially with the patch that adds ->d_manage()).  This handles transits from
directories during pathwalk, including automounting and skipping over
mountpoints (and holding processes with the next patch).

__follow_mount_rcu() will jump out of RCU-walk mode if it encounters an
automount point with nothing mounted on it.

follow_dotdot*() does not handle automounts as you don't want to trigger them
whilst following "..".

I've also extracted the mount/don't-mount logic from autofs4 and included it
here.  It makes the mount go ahead anyway if someone calls open() or creat(),
tries to traverse the directory, tries to chdir/chroot/etc. into the directory,
or sticks a '/' on the end of the pathname.  If they do a stat(), however,
they'll only trigger the automount if they didn't also say O_NOFOLLOW.

I've also added an inode flag (S_AUTOMOUNT) so that filesystems can mark their
inodes as automount points.  This flag is automatically propagated to the
dentry as DCACHE_NEED_AUTOMOUNT by __d_instantiate().  This saves NFS and could
save AFS a private flag bit apiece, but is not strictly necessary.  It would be
preferable to do the propagation in d_set_d_op(), but that doesn't normally
have access to the inode.

[AV: fixed breakage in case if __follow_mount_rcu() fails and nameidata_drop_rcu()
succeeds in RCU case of do_lookup(); we need to fall through to non-RCU case after
that, rather than just returning with ungrabbed *path]

Signed-off-by: David Howells 
Was-Acked-by: Ian Kent 
Signed-off-by: Al Viro

Turn d_set_d_op() BUG_ON() into WARN_ON_ONCE()

2011-01-14T21:26:18+00:00

It's indicative of a real problem, and it actually triggers with
autofs4, but the BUG_ON() is excessive.  The autofs4 case is being fixed
(to only set d_op in the ->lookup method) but not merged yet.  In the
meantime this gets the code limping along.

Reported-by: Alex Elder 
Cc: Ian Kent 
Cc: Nick Piggin 
Cc: Al Viro 
Signed-off-by: Linus Torvalds

fs: fix kernel-doc for dcache::prepend_path

2011-01-13T01:06:57+00:00

Fix function kernel-doc warning for prepend_path():

Warning(fs/dcache.c:1924): missing initial short description on line:

Signed-off-by: Randy Dunlap 
Cc: Alexander Viro 
Signed-off-by: Al Viro

fs: fix kernel-doc for dcache::d_validate

2011-01-13T01:06:55+00:00

Fix function parameter kernel-doc for d_validate():

Warning(fs/dcache.c:1495): No description found for parameter 'parent'
Warning(fs/dcache.c:1495): Excess function parameter 'dparent' description in 'd_validate'

Signed-off-by: Randy Dunlap 
Cc: Alexander Viro 
Signed-off-by: Al Viro

per-superblock default ->d_op

2011-01-13T01:02:34+00:00

Signed-off-by: Al Viro

fs: implement faster dentry memcmp

2011-01-07T06:50:32+00:00

The standard memcmp function on a Westmere system shows up hot in
profiles in the `git diff` workload (both parallel and single threaded),
and it is likely due to the costs associated with trapping into
microcode, and little opportunity to improve memory access (dentry
name is not likely to take up more than a cacheline).

So replace it with an open-coded byte comparison. This increases code
size by 8 bytes in the critical __d_lookup_rcu function, but the
speedup is huge, averaging 10 runs of each:

git diff st   user   sys   elapsed  CPU
before        1.15   2.57  3.82      97.1
after         1.14   2.35  3.61      96.8

git diff mt   user   sys   elapsed  CPU
before        1.27   3.85  1.46     349
after         1.26   3.54  1.43     333

Elapsed time for single threaded git diff at 95.0% confidence:
        -0.21  +/- 0.01
        -5.45% +/- 0.24%

It's -0.66% +/- 0.06% elapsed time on my Opteron, so rep cmp costs on the
fam10h seem to be relatively smaller, but there is still a win.

Signed-off-by: Nick Piggin

fs: prefetch inode data in dcache lookup

2011-01-07T06:50:32+00:00

This makes single threaded git diff -1.25% +/- 0.05% elapsed time on my
2s12c24t Westmere system, and -0.86% +/- 0.05% on my 2s8c Barcelona, by
prefetching the important first cacheline of the inode in while we do the
actual name compare and other operations on the dentry.

There was no measurable slowdown in the single file stat case, or the creat
case (where negative dentries would be common).

Signed-off-by: Nick Piggin