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  1. 02 Feb, 2009 4 commits
    • Tao Ma's avatar
      ocfs2: Access the xattr bucket only before modifying it. · 554e7f9e
      Tao Ma authored 
      In ocfs2_xattr_value_truncate, we may call b-tree codes which will
extend the journal transaction. It has a potential problem that it
may let the already-accessed-but-not-dirtied buffers gone. So we'd
better access the bucket after we call ocfs2_xattr_value_truncate.
And as for the root buffer for the xattr value, b-tree code will
acess and dirty it, so we don't need to worry about it.
Signed-off-by: default avatarTao Ma <tao.ma@oracle.com>
Signed-off-by: default avatarMark Fasheh <mfasheh@suse.com>
      554e7f9e
    • Joel Becker's avatar
      configfs: Silence lockdep on mkdir(), rmdir() and configfs_depend_item() · 0e033342
      Joel Becker authored 
      When attaching default groups (subdirs) of a new group (in mkdir() or
in configfs_register()), configfs recursively takes inode's mutexes
along the path from the parent of the new group to the default
subdirs. This is needed to ensure that the VFS will not race with
operations on these sub-dirs. This is safe for the following reasons:

- the VFS allows one to lock first an inode and second one of its
  children (The lock subclasses for this pattern are respectively
  I_MUTEX_PARENT and I_MUTEX_CHILD);
- from this rule any inode path can be recursively locked in
  descending order as long as it stays under a single mountpoint and
  does not follow symlinks.

Unfortunately lockdep does not know (yet?) how to handle such
recursion.

I've tried to use Peter Zijlstra's lock_set_subclass() helper to
upgrade i_mutexes from I_MUTEX_CHILD to I_MUTEX_PARENT when we know
that we might recursively lock some of their descendant, but this
usage does not seem to fit the purpose of lock_set_subclass() because
it leads to several i_mutex locked with subclass I_MUTEX_PARENT by
the same task.

>From inside configfs it is not possible to serialize those recursive
locking with a top-level one, because mkdir() and rmdir() are already
called with inodes locked by the VFS. So using some
mutex_lock_nest_lock() is not an option.

I am proposing two solutions:
1) one that wraps recursive mutex_lock()s with
   lockdep_off()/lockdep_on().
2) (as suggested earlier by Peter Zijlstra) one that puts the
   i_mutexes recursively locked in different classes based on their
   depth from the top-level config_group created. This
   induces an arbitrary limit (MAX_LOCK_DEPTH - 2 == 46) on the
   nesting of configfs default groups whenever lockdep is activated
   but this limit looks reasonably high. Unfortunately, this alos
   isolates VFS operations on configfs default groups from the others
   and thus lowers the chances to detect locking issues.

This patch implements solution 1).

Solution 2) looks better from lockdep's point of view, but fails with
configfs_depend_item(). This needs to rework the locking
scheme of configfs_depend_item() by removing the variable lock recursion
depth, and I think that it's doable thanks to the configfs_dirent_lock.
For now, let's stick to solution 1).
Signed-off-by: default avatarLouis Rilling <louis.rilling@kerlabs.com>
Acked-by: default avatarJoel Becker <joel.becker@oracle.com>
Signed-off-by: default avatarMark Fasheh <mfasheh@suse.com>
      0e033342
    • Jan Kara's avatar
      ocfs2: Fix possible deadlock in ocfs2_write_dquot() · f8afead7
      Jan Kara authored 
      It could happen that some limit has been set via quotactl() and in parallel
->mark_dirty() is called from another thread doing e.g. dquot_alloc_space(). In
such case ocfs2_write_dquot() must not try to sync the dquot because that needs
global quota lock but that ranks above transaction start.
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarMark Fasheh <mfasheh@suse.com>
      f8afead7
    • Jan Kara's avatar
      ocfs2: Push out dropping of dentry lock to ocfs2_wq · ea455f8a
      Jan Kara authored 
      Dropping of last reference to dentry lock is a complicated operation involving
dropping of reference to inode. This can get complicated and quota code in
particular needs to obtain some quota locks which leads to potential deadlock.
Thus we defer dropping of inode reference to ocfs2_wq.
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarMark Fasheh <mfasheh@suse.com>
      ea455f8a
  3. 01 Feb, 2009 1 commit
    • Linus Torvalds's avatar
      Manually revert "mlock: downgrade mmap sem while populating mlocked regions" · 27421e21
      Linus Torvalds authored 
      This essentially reverts commit 8edb08ca.

It downgraded our mmap semaphore to a read-lock while mlocking pages, in
order to allow other threads (and external accesses like "ps" et al) to
walk the vma lists and take page faults etc.  Which is a nice idea, but
the implementation does not work.

Because we cannot upgrade the lock back to a write lock without
releasing the mmap semaphore, the code had to release the lock entirely
and then re-take it as a writelock.  However, that meant that the caller
possibly lost the vma chain that it was following, since now another
thread could come in and mmap/munmap the range.

The code tried to work around that by just looking up the vma again and
erroring out if that happened, but quite frankly, that was just a buggy
hack that doesn't actually protect against anything (the other thread
could just have replaced the vma with another one instead of totally
unmapping it).

The only way to downgrade to a read map _reliably_ is to do it at the
end, which is likely the right thing to do: do all the 'vma' operations
with the write-lock held, then downgrade to a read after completing them
all, and then do the "populate the newly mlocked regions" while holding
just the read lock.  And then just drop the read-lock and return to user
space.

The (perhaps somewhat simpler) alternative is to just make all the
callers of mlock_vma_pages_range() know that the mmap lock got dropped,
and just re-grab the mmap semaphore if it needs to mlock more than one
vma region.

So we can do this "downgrade mmap sem while populating mlocked regions"
thing right, but the way it was done here was absolutely not correct.
Thus the revert, in the expectation that we will do it all correctly
some day.

Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@kernel.org
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      27421e21
  5. 31 Jan, 2009 15 commits
  7. 30 Jan, 2009 20 commits
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