Fixed a bug where zfs_zget could access a stale znode pointer when
the inode had already been removed from the inode cache via iput ->
iput_final -> ... -> zfs_zinactive but the corresponding SA handle
was still alive.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#180
Under Linux a dentry referencing an inode must be instantiated before
the inode is unlocked. To accomplish this without overly modifing
the core ZFS code the dentry it passed via the vattr_t. There are
cases such as replay when a dentry is not available. In which case
it is obviously not initialized at inode creation time, if a dentry
is needed it will be spliced as when required via d_lookup().
Now that KM_SLEEP is not defined as GFP_NOFS there is the possibility
of synchronous reclaim deadlocks. These deadlocks never existed in the
original OpenSolaris code because all memory reclaim on Solaris is done
asyncronously. Linux does both synchronous (direct) and asynchronous
(indirect) reclaim.
This commit addresses a deadlock caused by inode eviction. A KM_SLEEP
allocation may trigger direct memory reclaim and shrink the inode cache.
This can occur while a mutex in the array of ZFS_OBJ_HOLD mutexes is
held. Through the ->shrink_icache_memory()->evict()->zfs_inactive()->
zfs_zinactive() call path the same mutex may be reacquired resulting
in a deadlock. To avoid this deadlock the process must not reacquire
the mutex when it is already holding it.
This is a reasonable fix for now but longer term the ZFS_OBJ_HOLD
mutex locking should be reevaluated. This infrastructure already
prevents us from ever using the Linux lock dependency analysis tools,
and it may limit scalability.
It used to be the case that all KM_SLEEP allocations were GFS_NOFS.
Unfortunately this often resulted in the kernel being unable to
reclaim the ARC, inode, and dentry caches in a timely manor.
The fix was to make KM_SLEEP a GFP_KERNEL allocation in the SPL.
However, this increases the posibility of deadlocking the system
on a zfs write thread. If a zfs write thread attempts to perform
an allocation it may trigger synchronous reclaim. This reclaim
may attempt to flush dirty data/inode to disk to free memory.
Unforunately, this write cannot finish because the write thread
which would handle it is holding the previous transaction open.
Deadlock.
To avoid this all allocations in the zfs write thread path must
use KM_PUSHPAGE which prohibits synchronous reclaim for that
thread. In this way forward progress in ensured. The risk
with this change is I missed updating an allocation for the
write threads leaving an increased posibility of deadlock. If
any deadlocks remain they will be unlikely but we'll have to
make sure they all get fixed.
Due to an uninitialized variable files opened with O_APPEND may
overwrite the start of the file rather than append to it. This
was introduced accidentally when I removed the Solaris vnodes.
The zfs_range_lock_writer() function used to key off zf->z_vnode
to determine if a znode_t was for a zvol of zpl object. With
the removal of vnodes this was replaced by the flag zp->z_is_zvol.
This flag was used to control the append behavior for range locks.
Unfortunately, this value was never properly initialized after
the vnode removal. However, because most of memory is usually
zeros it happened to be set correctly most of the time making
the bug appear racy. Properly initializing zp->z_is_zvol to
zero completely resolves the problem with O_APPEND.
Closes#126
When I began work on the Posix layer it immediately became clear to
me that to integrate cleanly with the Linux VFS certain Solaris
specific things would have to go. One of these things was to elimate
as many Solaris specific types from the ZPL layer as possible. They
would be replaced with their Linux equivalents. This would not only
be good for performance, but for the general readability and health of
the code. The Solaris and Linux VFS are different beasts and should
be treated as such. Most of the code remains common for constructing
transactions and such, but there are subtle and important differenced
which need to be repsected.
This policy went quite for for certain types such as the vnode_t,
and it initially seemed to be working out well for the vattr_t. There
was a relatively small amount of related xvattr_t code I was forced to
comment out with HAVE_XVATTR. But it didn't look that hard to come
back soon and replace it all with a native Linux type.
However, after going doing this path with xvattr some distance it
clear that this code was woven in the ZPL more deeply than I thought.
In particular its hooks went very deep in to the ZPL replay code
and replacing it would not be as easy as I originally thought.
Rather than continue persuing replacing and removing this code I've
taken a step back and reevaluted things. This commit reverts many of
my previous commits which removed xvattr related code. It restores
much of the code to its original upstream state and now relies on
improved xvattr_t support in the zfs package itself.
The result of this is that much of the code which I had commented
out, which accidentally broke things like replay, is now back in
place and working. However, there may be a small performance
impact for getattr/setattr operations because they now require
a translation from native Linux to Solaris types. For now that's
a price I'm willing to pay. Once everything is completely functional
we can revisting the issue of removing the vattr_t/xvattr_t types.
Closes#111
Remove custom code to pack/unpack dev_t's. Under Linux all dev_t's
are an unsigned 32-bit value even on 64-bit platforms. The lower
20 bits are used for the minor number and the upper 12 for the major
number.
This means if your importing a pool from Solaris you may get strange
major/minor numbers. But it doesn't really matter because even if
we add compatibility code to translate the encoded Solaris major/minor
they won't do you any good under Linux. You will still need to
recreate the dev_t with a major/minor which maps to reserved major
numbers used under Linux.
Dropping this code also resolves 32-bit builds by removing the
offending 32-bit compatibility code.
Under Linux when creating a fifo or socket type device in the ZFS
filesystem it's critical that the rdev is stored in a SA. This
was already being correctly done for character and block devices,
but that logic needed to be extended to include FIFOs and sockets.
This patch takes care of device creation but a follow on patch
may still be required to verify that the dev_t is being correctly
packed/unpacked from the SA.
I appologize in advance why to many things ended up in this commit.
When it could be seperated in to a whole series of commits teasing
that all apart now would take considerable time and I'm not sure
there's much merrit in it. As such I'll just summerize the intent
of the changes which are all (or partly) in this commit. Broadly
the intent is to remove as much Solaris specific code as possible
and replace it with native Linux equivilants. More specifically:
1) Replace all instances of zfsvfs_t with zfs_sb_t. While the
type is largely the same calling it private super block data
rather than a zfsvfs is more consistent with how Linux names
this. While non critical it makes the code easier to read when
your thinking in Linux friendly VFS terms.
2) Replace vnode_t with struct inode. The Linux VFS doesn't have
the notion of a vnode and there's absolutely no good reason to
create one. There are in fact several good reasons to remove it.
It just adds overhead on Linux if we were to manage one, it
conplicates the code, and it likely will lead to bugs so there's
a good change it will be out of date. The code has been updated
to remove all need for this type.
3) Replace all vtype_t's with umode types. Along with this shift
all uses of types to mode bits. The Solaris code would pass a
vtype which is redundant with the Linux mode. Just update all the
code to use the Linux mode macros and remove this redundancy.
4) Remove using of vn_* helpers and replace where needed with
inode helpers. The big example here is creating iput_aync to
replace vn_rele_async. Other vn helpers will be addressed as
needed but they should be be emulated. They are a Solaris VFS'ism
and should simply be replaced with Linux equivilants.
5) Update znode alloc/free code. Under Linux it's common to
embed the inode specific data with the inode itself. This removes
the need for an extra memory allocation. In zfs this information
is called a znode and it now embeds the inode with it. Allocators
have been updated accordingly.
6) Minimal integration with the vfs flags for setting up the
super block and handling mount options has been added this
code will need to be refined but functionally it's all there.
This will be the first and last of these to large to review commits.
For portability reasons it's handy to be able to create a root
znode and basic filesystem components without requiring the full
cooperation of the VFS. We are committing to this to simply the
filesystem creations code.
The ZFS code is being restructured to act as a library and a stand
alone module. This allows us to leverage most of the existing code
with minimal modification. It also means we need to drop the Solaris
vfs/vnode functions they will be replaced by Linux equivilants and
updated to be Linux friendly.
For the moment we have left ZFS unchanged and it updates many values
as part of the znode. However, some of these values should be set
in the inode. For the moment this is handled by adding a function
called zfs_inode_update() which updates the inode based on the znode.
This is considered a workaround until we can systematically go
through the ZFS code and have it directly update the inode. At
which point zfs_update_inode() can be dropped entirely. Keeping
two copies of the same data isn't only inefficient it's a breeding
ground for bugs.
Under Linux the convention for filesystem specific data structure is
to embed it along with the generic vfs data structure. This differs
significantly from Solaris.
Since we want to integrates as cleanly with the Linux VFS as possible.
This changes modifies zfs_znode_alloc() to allocate a znode with an
embedded inode for use with the generic VFS. This is done by calling
iget_locked() which will allocate a new inode if needed by calling
sb->alloc_inode(). This function allocates enough memory for a
znode_t by returns a pointer to the inode structure for Linux's VFS.
This function is also responsible for setting the callback
znode->z_set_ops_inodes() which is used to register the correct
handlers for the inode.
Basic compilation of the bulk of zfs_znode.c has been enabled. After
much consideration it was decided to convert the existing vnode based
interfaces to more friendly Linux interfaces. The following commits
will systematically replace update the requiter interfaces. There
are of course pros and cons to this decision.
Pros:
* This simplifies intergration with Linux in the long term. There is
no longer any need to manage vnodes which are a foreign concept to
the Linux VFS.
* Improved long term maintainability.
* Minor performance improvements by removing vnode overhead.
Cons:
* Added work in the short term to modify multiple ZFS interfaces.
* Harder to pull in changes if we ever see any new code from Solaris.
* Mixed Solaris and Linux interfaces in some ZFS code.
Certain NFS/SMB share functionality is not yet in place. These
functions used to be wrapped with the generic HAVE_ZPL to prevent
them from being compiled. I still don't want them compiled but
I'm working toward eliminating the use of HAVE_ZPL. So I'm just
renaming the wrapper here to HAVE_SHARE. They still won't be
compiled until all the share issues are worked through. Share
support is the last missing piece from zfs_ioctl.c.
Unlike Solaris the Linux implementation embeds the inode in the
znode, and has no use for a vnode. So while it's true that fragmention
of the znode cache may occur it should not be worse than any of the
other Linux FS inode caches. Until proven that this is a problem it's
just added complexity we don't need.
These compiler warnings were introduced when code which was
previously #ifdef'ed out by HAVE_ZPL was re-added for use
by the posix layer. All of the following changes should be
obviously correct and will cause no semantic changes.
Fix non-c90 compliant code, for the most part these changes
simply deal with where a particular variable is declared.
Under c90 it must alway be done at the very start of a block.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
