Re: bug caused by removal of trans_mutex? (Was: Re: kernel BUG at fs/btrfs/extent-tree.c:6164!)

[Chris Mason <chris.mason@oracle.com>]

Excerpts from Yan, Zheng's message of 2011-06-13 10:58:35 -0400:
> The usage of trans_mutex in relocation code is subtle. It controls
> interaction of relocation
> with transaction start, transaction commit and snapshot creation.
> Simple replacing
> trans_mutex with trans_lock is wrong.

What requirements of the relocation stuff are we currently missing?  I'=
d
rather add extra waiting for relocation than go back to the mutex.

-chris

>=20
> On Mon, Jun 13, 2011 at 3:13 PM, Li Zefan <lizf@cn.fujitsu.com> wrote=
:
> > Cc: Josef
> >
> >>>>>>>>> I encountered following panic using 'btrfs-unstable + for-l=
inus'
> >>>>>>>>> kernel.
> >>>>>>>>>
> >>>>>>>>> I ran "btrfs fi bal /test5" command, and mount option of /t=
est5
> >>>>>>>>> is as follows:
> >>>>>>>>>
> >>>>>>>>> =C2=A0/dev/sdc3 on /test5 type btrfs (rw,space_cache,compre=
ss=3Dlzo,inode_cache)
> >>>>>>>>>
> >>>>>>>> So, just a "btrfs fi bal" would lead to the bug?
> >>>>>>> I think so.
> >>>
> >>> It should be specific to the inode caching code. =C2=A0The balanc=
ing code is
> >>> finding the inode map cache extents, but it doesn't know how to r=
elocate
> >>> them.
> >>
> >> However, the panic has occurred even if inode_cahce is turned off.
> >> Is this another problem?
> >>
> >
> > I don't think free inode cache isthe cause of the bug here (even if=
 inode_cache
> > is turned on).
> >
> > What I have found out is:
> >
> > 1. git checkout a4abeea41adfa3c143c289045f4625dfaeba2212
> >
> > So the top commit is the removal of trans_mutex and no delayed_inod=
e patch
> > or free inode cache patchset in the tree, and bug can be triggered.
> >
> > 2. git checkout 2a1eb4614d984d5cd4c928784e9afcf5c07f93be
> >
> > So the top commit is the one before trans_mutex removal, and no bug=
 triggered.
> >
> > 3. test linus' tree
> >
> > bug triggered.
> >
> > 4. revert that suspicoius commit manually from linus' tree
> >
> > no bug.
> >
> > so either that commit is buggy or it reveals some bugs covered by t=
he trans_mutex.
> >
> > --
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