Attempt to create a new file in a snapshot crashes the MDS

Attempt to create a new file in a snapshot crashes the MDS

[Adam C. Emerson]

I know it's not supported, but I tried it out to see what kind of
error behaviour I would get.

The following were preformed on a simple ceph filesystem (one monitor,
one mds, one osd all on the same machine) running current unstable
with the filesystem mounted via cfuse:

/mnt# mkdir foo
/mnt# cd foo
/mnt/foo# cat > something
These are the contents of the file.
/mnt/foo# cd .snap
/mnt/foo/.snap# mkdir old
/mnt/foo/.snap# cd ..
/mnt/foo# cat > something
These are different contents of the file.
/mnt/foo# cd .snap
/mnt/foo/.snap# ls
old/
/mnt/foo/.snap# cd old 
root@seasalt:/mnt/foo/.snap/old# ls
something
/mnt/foo/.snap/old# cat something 
These are the contents of the file.
/mnt/foo/.snap/old# cat > something
zsh: invalid argument: something
/mnt/foo/.snap/old# cat > somthingelse
These are divergent contents.

This last command hangs, and in the MDS log I find:
mds/CDir.cc: In function 'CDentry* CDir::add_null_dentry(const std::string&, snapid_t, snapid_t)':
mds/CDir.cc:225: FAILED assert(lookup_exact_snap(dname, last) == 0)

Thank you very much.

Re: Attempt to create a new file in a snapshot crashes the MDS

[Wido den Hollander]

Hi Adam,

Could you add "debug mds = 20" in your ceph.conf and retry?

There should also be a file "core" in /, this is a dump which you can
use to make a backtrace with gdb (if you have the debug symbols).

gdb /usr/bin/cmds /core
gdb> bt

Could you try this?

-- 
Met vriendelijke groet,

Wido den Hollander
CTO
Contact: http://www.pcextreme.nl/contact


On Fri, 2010-07-09 at 19:22 +0000, Adam C. Emerson wrote:
> I know it's not supported, but I tried it out to see what kind of
> error behaviour I would get.
> 
> The following were preformed on a simple ceph filesystem (one monitor,
> one mds, one osd all on the same machine) running current unstable
> with the filesystem mounted via cfuse:
> 
> /mnt# mkdir foo
> /mnt# cd foo
> /mnt/foo# cat > something
> These are the contents of the file.
> /mnt/foo# cd .snap
> /mnt/foo/.snap# mkdir old
> /mnt/foo/.snap# cd ..
> /mnt/foo# cat > something
> These are different contents of the file.
> /mnt/foo# cd .snap
> /mnt/foo/.snap# ls
> old/
> /mnt/foo/.snap# cd old 
> root@seasalt:/mnt/foo/.snap/old# ls
> something
> /mnt/foo/.snap/old# cat something 
> These are the contents of the file.
> /mnt/foo/.snap/old# cat > something
> zsh: invalid argument: something
> /mnt/foo/.snap/old# cat > somthingelse
> These are divergent contents.
> 
> This last command hangs, and in the MDS log I find:
> mds/CDir.cc: In function 'CDentry* CDir::add_null_dentry(const std::string&, snapid_t, snapid_t)':
> mds/CDir.cc:225: FAILED assert(lookup_exact_snap(dname, last) == 0)
> 
> Thank you very much.
> --
> To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Attempt to create a new file in a snapshot crashes the MDS

[Sage Weil]

This is primarily a cfuse bug.. it should generate EROFS locally.  The 
MDS should also not crash. 

In any case, we shouldn't need the debug output.  :)

Thanks for the bug report!
sage

On Fri, 9 Jul 2010, Wido den Hollander wrote:

> Hi Adam,
> 
> Could you add "debug mds = 20" in your ceph.conf and retry?
> 
> There should also be a file "core" in /, this is a dump which you can
> use to make a backtrace with gdb (if you have the debug symbols).
> 
> gdb /usr/bin/cmds /core
> gdb> bt
> 
> Could you try this?
> 
> -- 
> Met vriendelijke groet,
> 
> Wido den Hollander
> CTO
> Contact: http://www.pcextreme.nl/contact
> 
> 
> On Fri, 2010-07-09 at 19:22 +0000, Adam C. Emerson wrote:
> > I know it's not supported, but I tried it out to see what kind of
> > error behaviour I would get.
> > 
> > The following were preformed on a simple ceph filesystem (one monitor,
> > one mds, one osd all on the same machine) running current unstable
> > with the filesystem mounted via cfuse:
> > 
> > /mnt# mkdir foo
> > /mnt# cd foo
> > /mnt/foo# cat > something
> > These are the contents of the file.
> > /mnt/foo# cd .snap
> > /mnt/foo/.snap# mkdir old
> > /mnt/foo/.snap# cd ..
> > /mnt/foo# cat > something
> > These are different contents of the file.
> > /mnt/foo# cd .snap
> > /mnt/foo/.snap# ls
> > old/
> > /mnt/foo/.snap# cd old 
> > root@seasalt:/mnt/foo/.snap/old# ls
> > something
> > /mnt/foo/.snap/old# cat something 
> > These are the contents of the file.
> > /mnt/foo/.snap/old# cat > something
> > zsh: invalid argument: something
> > /mnt/foo/.snap/old# cat > somthingelse
> > These are divergent contents.
> > 
> > This last command hangs, and in the MDS log I find:
> > mds/CDir.cc: In function 'CDentry* CDir::add_null_dentry(const std::string&, snapid_t, snapid_t)':
> > mds/CDir.cc:225: FAILED assert(lookup_exact_snap(dname, last) == 0)
> > 
> > Thank you very much.
> > --
> > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 
> --
> To unsubscribe from this list: send the line "unsubscribe ceph-devel" in
> the body of a message to majordomo@vger.kernel.org
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> 
>