Re: [PATCH/RFC] fscache/cachefiles versus btrfs

[NeilBrown <neilb@suse.de>]

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On Fri, 10 Apr 2015 11:24:31 +1000 NeilBrown <neilb@suse.de> wrote:

> On Thu, 09 Apr 2015 10:23:08 +0100 David Howells <dhowells@redhat.com> wrote:
> 
> > NeilBrown <neilb@suse.de> wrote:
> > 
> > >  Is there a better way?  Could a better way be created?  Maybe
> > >  SEEK_DATA_RELIABLE ??
> > 
> > fiemap() maybe?
> > 
> > > Also, if you do try to use fscache on btrfs with 3.19, then nothing gets
> > > cached (as expected) and with a heavy load you can lose a race and get an
> > > asserting fail in fscache_enqueue_operation
> > 
> > Do you have the patches here applied?
> > 
> > 	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=fscache-fixes
> > 
> 
> Do I don't.  I had looked through them and while they did seem to be
> addressing similar sorts of races, nothing seems like an obvious match.
> I haven't been able to reproduce the BUG_ON myself.  I only have a report
> of it repeatedly affecting someone else:
> 
>   https://bugzilla.opensuse.org/show_bug.cgi?id=908706
> 
> I'll probably have to be happy with fixing usage on btrfs, and hope the other
> bug is fixed already or doesn't become a problem.

I managed to reproduce the bug, and when I applied your patches I cannot any
more.  So it looks like you've fixed it - thanks.

That just leave the bmap issue.  I'll post a patch which causes lseek to be
used when the fs says that is OK.

Thanks,
NeilBrown

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