Re: Leveldb in google-chrome incompatible with btrfs?

[Marc MERLIN <marc@merlins.org>]

On Thu, Jul 06, 2017 at 04:01:41PM -0700, Omar Sandoval wrote:
> What doesn't add up about your bug report is that your CURRENT points to
> a MANIFEST-010814 way behind all of the other files in that directory,
> which are numbered 022745+. If there were a bug here, I'd expect the
> stale MANIFEST file would be one older than the new one. The filenames
> seem to be allocated sequentially, so that old MANIFEST file CURRENT
> refers to must be really old, which doesn't make sense. I don't see how
> Btrfs would screw that up :) I'd be interested to see if you can make
> the same condition trigger again.
> 

First, thanks for looking at it.

Second, you are right on the numbers being so far apart that something was
wrong. I checked my snapshots, and I've been carrying that MANIFEST-010814
for a long time.
In other words, it's a old stale manifest that never got deleted.

The new real old one apparently got deleted, the new one was created but
didn't make it to disk, but the pointer in CURRENT did get repointed to the
new one that never made it to actual disk.

So I think what happened is something like this:
MANIFEST-new got created
echo MANIFEST-new > CURRENT
MANIFEST-old got deleted
system crashed

MANIFEST-old was indeed deleted, and MANIFEST-new never made it to disk.

Does that sound more plausible?

As for redoing this at will, apparently I may have been hit by the skylake
hyperthreading CPU bug that I just installed a microcode update for, which
was causing random crashes, which hopefully are now solved.
I can't say if those in turn messed with btrfs writing data, but I'd rather
not recreate this since it's my real filesystem I care about and don't want
to corrupt on purpose :)
That said, the google-chrome on my previous haswell CPU also had routine
problems when restarting chrome, although at this point I don't know if they
were due to leveldb or sqlite or something else.
I'm just mentioning this to say that I'm pretty sure that the haswell HT bug
isn't the sole culprit of this problem, likely just the trigger of some of
my crashes.

Hope this helps
Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/