The four patches in this series fix deadlocks with quotas of pagelock (the
problem was lock inversion on PageLock and transaction start - quota code
needed to first start a transaction and then write the data which subsequently
needed acquisition of PageLock while the standard ordering - PageLock first
and transaction start later - was used e.g.  by pdflush).  They implement a
new way of quota access to disk: Every filesystem that would like to implement
quotas now has to provide quota_read() and quota_write() functions.  These
functions must obey quota lock ordering (in particular they should not take
PageLock inside a transaction).

The first patch implements the changes in the quota core, the other three
patches implement needed functions in ext2, ext3 and reiserfs.  The patch for
reiserfs also fixes several other lock inversion problems (similar as ext3
had) and implements the journaled quota functionality (which comes almost for
free after the locking fixes...).

The quota core patch makes quota support in other filesystems (except XFS
which implements everything on its own ;)) unfunctional (quotaon() will refuse
to turn on quotas on them).  When the patches get reasonable wide testing and
it will seem that no major changes will be needed I can make fixes also for
the other filesystems (JFS, UDF, UFS).

This patch:

The patch implements the new way of quota io in the quota core.  Every
filesystem wanting to support quotas has to provide functions quota_read()
and quota_write() obeying quota locking rules.  As the writes and reads
bypass the pagecache there is some ugly stuff ensuring that userspace can
see all the data after quotaoff() (or Q_SYNC quotactl).  In future I plan
to make quota files inaccessible from userspace (with the exception of
quotacheck(8) which will take care about the cache flushing and such stuff
itself) so that this synchronization stuff can be removed...

The rewrite of the quota core. Quota uses the filesystem read() and write()
functions no more to avoid possible deadlocks on PageLock. From now on every
filesystem supporting quotas must provide functions quota_read() and
quota_write() which obey the quota locking rules (e.g. they cannot acquire the
PageLock).
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>