[Devel] [PATCH] fuse: hotfix truncate_pagecache() issue

[Miklos Szeredi]

On Thu, Aug 29, 2013 at 3:01 PM, Maxim Patlasov <mpatlasov at parallels.com> wrote:
> The patch looks fine, but it solves only one side of the problem (exactly
> what you formulated above). Another side is opposite: truncating page cache
> too late, when the state of inode changed significantly. The beginning may
> be as in the scenario above: fuse_dentry_revalidate() discovered that i_size
> changed (due to our own fuse_do_setattr()) and is going to call
> truncate_pagecache() for some 'new_size' it believes valid right now. But by
> the time that particular truncate_pagecache() is called, a lot of things may
> happen:
>
> 1) fuse_do_setattr() called truncate_pagecache() according to your patch
> 2) the file was extended either by write(2) or ftruncate(2) or fallocate(2).
> 3) mmap-ed write make a page in the extended region dirty
>
> The result will be the lost of data user wrote on the step '3)'. (my patch
> solves the issue at least for all cases w/o external changes)

I get it.

Could you please resend the patch with all these failure cases
described in the header?

Thanks,
Miklos