We can easily set the extsize flag without setting an extent size
hint, or one that evaluates to zero. Historically the di_extsize
field was only used when it was non-zero, but the commit
"Cleanup inode extent size hint extraction"
broke this. Restore the old behaviour, thus fixing xfsqa 090 with
a debug kernel.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Currently both xfs_rtpick_extent and xfs_rtallocate_extent call
xfs_trans_iget to grab and lock the rt bitmap inode, which results in a
deadlock since the removal of the lock recursion counters in commit
"xfs: simplify inode to transaction joining"
Fix this by acquiring and locking the inode in xfs_bmap_rtalloc before
calling into xfs_rtpick_extent and xfs_rtallocate_extent.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
When filling in the middle of a previous delayed allocation in
xfs_bmap_add_extent_delay_real, set br_startblock of the new delay
extent to the right to nullstartblock instead of 0 before inserting
the extent into the ifork (xfs_iext_insert), rather than setting
br_startblock afterward.
Adding the extent into the ifork with br_startblock=0 can lead to
the extent being copied into the btree by xfs_bmap_extent_to_btree
if we happen to convert from extents format to btree format before
updating br_startblock with the correct value. The unexpected
addition of this delay extent to the btree can cause subsequent
XFS_WANT_CORRUPTED_GOTO filesystem shutdown in several
xfs_bmap_add_extent_delay_real cases where we are converting a delay
extent to real and unexpectedly find an extent already inserted.
For example:
911 case BMAP_LEFT_FILLING:
912 /*
913 * Filling in the first part of a previous delayed allocation.
914 * The left neighbor is not contiguous.
915 */
916 trace_xfs_bmap_pre_update(ip, idx, state, _THIS_IP_);
917 xfs_bmbt_set_startoff(ep, new_endoff);
918 temp = PREV.br_blockcount - new->br_blockcount;
919 xfs_bmbt_set_blockcount(ep, temp);
920 xfs_iext_insert(ip, idx, 1, new, state);
921 ip->i_df.if_lastex = idx;
922 ip->i_d.di_nextents++;
923 if (cur == NULL)
924 rval = XFS_ILOG_CORE | XFS_ILOG_DEXT;
925 else {
926 rval = XFS_ILOG_CORE;
927 if ((error = xfs_bmbt_lookup_eq(cur, new->br_startoff,
928 new->br_startblock, new->br_blockcount,
929 &i)))
930 goto done;
931 XFS_WANT_CORRUPTED_GOTO(i == 0, done);
With the bogus extent in the btree we shutdown the filesystem at
931. The conversion from extents to btree format happens when the
number of extents in the inode increases above ip->i_df.if_ext_max.
xfs_bmap_extent_to_btree copies extents from the ifork into the
btree, ignoring all delalloc extents which are denoted by
br_startblock having some value of nullstartblock.
SGI-PV: 1013221
Signed-off-by: Ben Myers <bpm@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Alex Elder <aelder@sgi.com>
Commit 368e136 ("xfs: remove duplicate code from dquot reclaim") fails
to unlock the dquot freelist when the number of loop restarts is
exceeded in xfs_qm_dqreclaim_one(). This causes hangs in memory
reclaim.
Rework the loop control logic into an unwind stack that all the
different cases jump into. This means there is only one set of code
that processes the loop exit criteria, and simplifies the unlocking
of all the items from different points in the loop. It also fixes a
double increment of the restart counter from the qi_dqlist_lock
case.
Reported-by: Malcolm Scott <lkml@malc.org.uk>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Alex Elder <aelder@sgi.com>
Failure to commit a transaction into the CIL is not handled
correctly. This currently can only happen when racing with a
shutdown and requires an explicit shutdown check, so it rare and can
be avoided. Remove the shutdown check and make the CIL commit a void
function to indicate it will always succeed, thereby removing the
incorrectly handled failure case.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
The extent size hint can be set to larger than an AG. This means
that the alignment process can push the range to be allocated
outside the bounds of the AG, resulting in assert failures or
corrupted bmbt records. Similarly, if the extsize is larger than the
maximum extent size supported, the alignment process will produce
extents that are too large to fit into the bmbt records, resulting
in a different type of assert/corruption failure.
Fix this by limiting extsize at the time іt is set firstly to be
less than MAXEXTLEN, then to be a maximum of half the size of the
AGs in the filesystem for non-realtime inodes. Realtime inodes do
not allocate out of AGs, so don't have to be restricted by the size
of AGs.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
When doing delayed allocation, if the allocation size is for a
maximally sized extent, extent size alignment can push it over this
limit. This results in an assert failure in xfs_bmbt_set_allf() as
the extent length is too large to find in the extent record.
Fix this by ensuring that we allow for space that extent size
alignment requires (up to 2 * (extsize -1) blocks as we have to
handle both head and tail alignment) when limiting the maximum size
of the extent.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Delayed allocation extents can be larger than AGs, so when trying to
convert a large range we may scan every AG inside
xfs_bmap_alloc_nullfb() trying to find an AG with a size larger than
an AG. We should stop when we find the first AG with a maximum
possible allocation size. This causes excessive CPU usage when there
are lots of AGs.
The same problem occurs when doing preallocation of a range larger
than an AG.
Fix the problem by limiting real allocation lengths to the maximum
that an AG can support. This means if we have empty AGs, we'll stop
the search at the first of them. If there are no empty AGs, we'll
still scan them all, but that is a different problem....
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
rounddown_power_of_2() returns an undefined result when passed a
value of zero. The specualtive delayed allocation code is doing this
when the inode is zero length. Hence occasionally the preallocation
is much, much larger than is necessary (e.g. 8GB for a 270 _byte_
file). Ensure we don't even pass a zero value to this function so
the result of preallocation is always the desired size.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
After test 139, kmemleak shows:
unreferenced object 0xffff880078b405d8 (size 400):
comm "xfs_io", pid 4904, jiffies 4294909383 (age 1186.728s)
hex dump (first 32 bytes):
60 c1 17 79 00 88 ff ff 60 c1 17 79 00 88 ff ff `..y....`..y....
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<ffffffff81afb04d>] kmemleak_alloc+0x2d/0x60
[<ffffffff8115c6cf>] kmem_cache_alloc+0x13f/0x2b0
[<ffffffff814aaa97>] kmem_zone_alloc+0x77/0xf0
[<ffffffff814aab2e>] kmem_zone_zalloc+0x1e/0x50
[<ffffffff8147cd6b>] xfs_efi_init+0x4b/0xb0
[<ffffffff814a4ee8>] xfs_trans_get_efi+0x58/0x90
[<ffffffff81455fab>] xfs_bmap_finish+0x8b/0x1d0
[<ffffffff814851b4>] xfs_itruncate_finish+0x2c4/0x5d0
[<ffffffff814a970f>] xfs_setattr+0x8df/0xa70
[<ffffffff814b5c7b>] xfs_vn_setattr+0x1b/0x20
[<ffffffff8117dc00>] notify_change+0x170/0x2e0
[<ffffffff81163bf6>] do_truncate+0x66/0xa0
[<ffffffff81163d0b>] sys_ftruncate+0xdb/0xe0
[<ffffffff8103a002>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff
The cause of the leak is that the "remove" parameter of IOP_UNPIN()
is never set when a CIL push is aborted. This means that the EFI
item is never freed if it was in the push being cancelled. The
problem is specific to delayed logging, but has uncovered a couple
of problems with the handling of IOP_UNPIN(remove).
Firstly, we cannot safely call xfs_trans_del_item() from IOP_UNPIN()
in the CIL commit failure path or the iclog write failure path
because for delayed loging we have no transaction context. Hence we
must only call xfs_trans_del_item() if the log item being unpinned
has an active log item descriptor.
Secondly, xfs_trans_uncommit() does not handle log item descriptor
freeing during the traversal of log items on a transaction. It can
reference a freed log item descriptor when unpinning an EFI item.
Hence it needs to use a safe list traversal method to allow items to
be removed from the transaction during IOP_UNPIN().
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Alex Elder <aelder@sgi.com>
The latter is called only when both ino and dentry are about to
be freed, so cleaning ->d_fsdata and ->dentry is pointless.
Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
split init_ino into new_ino and clean_ino; the former is
what used to be init_ino(NULL, sbi), the latter is for cases
where we passed non-NULL ino. Lose unused arguments.
Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
It's used only to pass the length of symlink body to
autofs4_get_inode() in autofs4_dir_symlink(). We can
bloody well set inode->i_size in autofs4_dir_symlink()
directly and be done with that.
Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
In all cases we'd set inf->mode to know value just before
passing it to autofs4_get_inode(). That kills the need
to store it in autofs_info and pass it to autofs_init_ino()
Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Kill it. Mind you, it's been an obfuscated call of autofs4_init_ino()
ever since 2.3.99pre6-4...
Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
gets rid of all ->free()/->u.symlink machinery in autofs; we simply
keep symlink bodies in inode->i_private and free them in ->evict_inode().
Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
oz_mode isn't defined any more, use autofs4_oz_mode(sbi) instead.
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
There is a ref count problem in fs/namei.c:do_lookup().
When walking in ref-walk mode, if follow_managed() returns a fail we
need to drop dentry and possibly vfsmount. Clean up properly,
as we do in the other caller of follow_managed().
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
The initialization condition in fs/autofs4/expire.c:get_next_positive_dentry()
appears to be incorrect. If prev == NULL I believe that root should be
returned.
Further down, at the current dentry check for it being simple_positive()
it looks like the d_lock for dentry p should be dropped instead of dentry
ret, otherwise when p is assinged to ret we end up with no lock on p and
a lost lock on ret, which leads to a deadlock.
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable: (25 commits)
Btrfs: forced readonly mounts on errors
btrfs: Require CAP_SYS_ADMIN for filesystem rebalance
Btrfs: don't warn if we get ENOSPC in btrfs_block_rsv_check
btrfs: Fix memory leak in btrfs_read_fs_root_no_radix()
btrfs: check NULL or not
btrfs: Don't pass NULL ptr to func that may deref it.
btrfs: mount failure return value fix
btrfs: Mem leak in btrfs_get_acl()
btrfs: fix wrong free space information of btrfs
btrfs: make the chunk allocator utilize the devices better
btrfs: restructure find_free_dev_extent()
btrfs: fix wrong calculation of stripe size
btrfs: try to reclaim some space when chunk allocation fails
btrfs: fix wrong data space statistics
fs/btrfs: Fix build of ctree
Btrfs: fix off by one while setting block groups readonly
Btrfs: Add BTRFS_IOC_SUBVOL_GETFLAGS/SETFLAGS ioctls
Btrfs: Add readonly snapshots support
Btrfs: Refactor btrfs_ioctl_snap_create()
btrfs: Extract duplicate decompress code
...
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ecryptfs/ecryptfs-2.6:
ecryptfs: remove unnecessary decrypt when extending a file
ecryptfs: Fix ecryptfs_printk() size_t warnings
fs/ecryptfs: Add printf format/argument verification and fix fallout
ecryptfs: fixed testing of file descriptor flags
ecryptfs: test lower_file pointer when lower_file_mutex is locked
ecryptfs: missing initialization of the superblock 'magic' field
ecryptfs: moved ECRYPTFS_SUPER_MAGIC definition to linux/magic.h
ecryptfs: fix truncation error in ecryptfs_read_update_atime
On platforms that call panic() inside their BUG() macro (m68k/sun3, and
all platforms that don't set HAVE_ARCH_BUG), compilation fails with:
| fs/xfs/support/debug.c: In function ‘xfs_cmn_err’:
| fs/xfs/support/debug.c:92: error: called object ‘panic’ is not a function
as the local variable "panic" conflicts with the "panic()" function.
Rename the local variable to resolve this.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This patch comes from "Forced readonly mounts on errors" ideas.
As we know, this is the first step in being more fault tolerant of disk
corruptions instead of just using BUG() statements.
The major content:
- add a framework for generating errors that should result in filesystems
going readonly.
- keep FS state in disk super block.
- make sure that all of resource will be freed and released at umount time.
- make sure that fter FS is forced readonly on error, there will be no more
disk change before FS is corrected. For this, we should stop write operation.
After this patch is applied, the conversion from BUG() to such a framework can
happen incrementally.
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
* git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6:
cifs: add cruid= mount option
cifs: cFYI the entire error code in map_smb_to_linux_error
* git://git.infradead.org/mtd-2.6: (59 commits)
mtd: mtdpart: disallow reading OOB past the end of the partition
mtd: pxa3xx_nand: NULL dereference in pxa3xx_nand_probe
UBI: use mtd->writebufsize to set minimal I/O unit size
mtd: initialize writebufsize in the MTD object of a partition
mtd: onenand: add mtd->writebufsize initialization
mtd: nand: add mtd->writebufsize initialization
mtd: cfi: add writebufsize initialization
mtd: add writebufsize field to mtd_info struct
mtd: OneNAND: OMAP2/3: prevent regulator sleeping while OneNAND is in use
mtd: OneNAND: add enable / disable methods to onenand_chip
mtd: m25p80: Fix JEDEC ID for AT26DF321
mtd: txx9ndfmc: limit transfer bytes to 512 (ECC provides 6 bytes max)
mtd: cfi_cmdset_0002: add support for Samsung K8D3x16UxC NOR chips
mtd: cfi_cmdset_0002: add support for Samsung K8D6x16UxM NOR chips
mtd: nand: ams-delta: drop omap_read/write, use ioremap
mtd: m25p80: add debugging trace in sst_write
mtd: nand: ams-delta: select for built-in by default
mtd: OneNAND: lighten scary initial bad block messages
mtd: OneNAND: OMAP2/3: add support for command line partitioning
mtd: nand: rearrange ONFI revision checking, add ONFI 2.3
...
Fix up trivial conflict in drivers/mtd/Kconfig as per DavidW.
Removes an unecessary page decrypt from ecryptfs_begin_write when the
page is beyond the current file size. Previously, the call to
ecryptfs_decrypt_page would result in a read of 0 bytes, but still
attempt to decrypt an entire page. This patch detects that case and
merely zeros the page before marking it up-to-date.
Signed-off-by: Frank Swiderski <fes@chromium.org>
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
Commit cb55d21f6fa19d8c6c2680d90317ce88c1f57269 revealed a number of
missing 'z' length modifiers in calls to ecryptfs_printk() when
printing variables of type size_t. This patch fixes those compiler
warnings.
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
Add __attribute__((format... to __ecryptfs_printk
Make formats and arguments match.
Add casts to (unsigned long long) for %llu.
Signed-off-by: Joe Perches <joe@perches.com>
[tyhicks: 80 columns cleanup and fixed typo]
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
This patch prevents the lower_file pointer in the 'ecryptfs_inode_info'
structure to be checked when the mutex 'lower_file_mutex' is not locked.
Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
This patch initializes the 'magic' field of ecryptfs filesystems to
ECRYPTFS_SUPER_MAGIC.
Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
[tyhicks: merge with 66cb76666d]
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
The definition of ECRYPTFS_SUPER_MAGIC has been moved to the include
file 'linux/magic.h' to become available to other kernel subsystems.
Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
This is similar to the bug found in direct-io not so long ago.
Fix up truncation (ssize_t->int). This only matters with >2G
reads/writes, which the kernel doesn't permit.
Signed-off-by: Edward Shishkin <edward.shishkin@gmail.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Eric Sandeen <esandeen@redhat.com>
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
The fi_extents_start field of struct fiemap_extent_info is a
user pointer but was not marked as __user. This makes sparse
emit following warnings:
CHECK fs/ioctl.c
fs/ioctl.c:114:26: warning: incorrect type in argument 1 (different address spaces)
fs/ioctl.c:114:26: expected void [noderef] <asn:1>*dst
fs/ioctl.c:114:26: got struct fiemap_extent *[assigned] dest
fs/ioctl.c:202:14: warning: incorrect type in argument 1 (different address spaces)
fs/ioctl.c:202:14: expected void const volatile [noderef] <asn:1>*<noident>
fs/ioctl.c:202:14: got struct fiemap_extent *[assigned] fi_extents_start
fs/ioctl.c:212:27: warning: incorrect type in argument 1 (different address spaces)
fs/ioctl.c:212:27: expected void [noderef] <asn:1>*dst
fs/ioctl.c:212:27: got char *<noident>
Also add 'ufiemap' variable to eliminate unnecessary casts.
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This fixed a case that 'sparse' spotted where hpfs_setattr has an error return
that didn't go through it's path that unlocks.
This is against git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
version 6313e3c217.
Build tested only, I don't have an hpfs file system to test.
Dave
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
f_flags and f_spare fields were not copied to userspace when
compat_sys_[f]statfs64 called.
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
The commit 7ed1ee6118 ("Take statfs variants to fs/statfs.c")
separates out statfs syscalls from fs/open.c. Thus the comment
should be changed also.
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Jiri Kosina <trivial@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
*@ret_pointer is initialized to @fast_pointer thus the assignment is
redundant.
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
- Fix a kconfig unmet dependency warning.
- Remove the comment that identifies which filesystems use POSIX ACL
utility routines.
- Move the FS_POSIX_ACL symbol outside of the BLOCK symbol if/endif block
because its functions do not depend on BLOCK and some of the filesystems
that use it do not depend on BLOCK.
warning: (GENERIC_ACL && JFFS2_FS_POSIX_ACL && NFSD_V4 && NFS_ACL_SUPPORT && 9P_FS_POSIX_ACL) selects FS_POSIX_ACL which has unmet direct dependencies (BLOCK)
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
There's an unlikely() in fget_light() that assumes the file ref count
will be 1. Running the annotate branch profiler on a desktop that is
performing daily tasks (running firefox, evolution, xchat and is also part
of a distcc farm), it shows that the ref count is not 1 that often.
correct incorrect % Function File Line
------- --------- - -------- ---- ----
1035099358 6209599193 85 fget_light file_table.c 315
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Currently all filesystems except XFS implement fallocate asynchronously,
while XFS forced a commit. Both of these are suboptimal - in case of O_SYNC
I/O we really want our allocation on disk, especially for the !KEEP_SIZE
case where we actually grow the file with user-visible zeroes. On the
other hand always commiting the transaction is a bad idea for fast-path
uses of fallocate like for example in recent Samba versions. Given
that block allocation is a data plane operation anyway change it from
an inode operation to a file operation so that we have the file structure
available that lets us check for O_SYNC.
This also includes moving the code around for a few of the filesystems,
and remove the already unnedded S_ISDIR checks given that we only wire
up fallocate for regular files.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Instead of various home grown checks that might need updates for new
flags just check for any bit outside the mask of the features supported
by the filesystem. This makes the check future proof for any newly
added flag.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
do_add_mount() and mnt_clear_expiry() are not needed outside of
namespace.c anymore, now that namei has finish_automount() to
use.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
That gets rid of the kludge in finish_automount() - we need
to keep refcount on the vfsmount as-is until we evict it from
expiry list.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
