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    SubjectRe: [PATCH 2/2] fuse: wait for writeback in fuse_file_fallocate() -v2
    On 09/11/2013 02:12 PM, Miklos Szeredi wrote:
    > On Fri, Aug 30, 2013 at 1:33 PM, Maxim Patlasov <mpatlasov@parallels.com> wrote:
    >> 08/30/2013 01:13 PM, Miklos Szeredi пишет:
    >>
    >>> On Thu, Aug 29, 2013 at 6:41 PM, Miklos Szeredi <miklos@szeredi.hu> wrote:
    >>>> BTW, isn't it enough to do the filemap_write_and_wait() *plus* the
    >>>> fuse_set_nowrite()?
    >>> Thought about it a bit and I think this should do fine.
    >>>
    >>> Any writes before the fallocate will go trough before the fallocate.
    >>> i_mutex guarantees that only one instance of fuse_set_nowrite() is
    >>> running. Any mmaped writes during the fallocate() will go after the
    >>> fallocate request and the page cache truncation and that's fine too.
    >>> Page cache is consistent since it doens't contain pages for those
    >>> writes to the hole. Subsequent reads to that area will fill them in.
    >>>
    >>> Any other concerns?
    >>
    >> No. What you suggest looks as a neat and correct solution. I'll resend the
    >> updated patch after some testing (since now till Monday).
    >>
    >> As for proof-of-correctness, all you wrote above is correct, but the first
    >> point had been boiling my mind for a while. I came to the following
    >> reasoning (hopefully it is what you meant):
    >>
    >> The fact that filemap_write_and_wait() returned infers that
    >> end_page_writeback() was called for all relevant pages. And fuse doesn't
    >> call it before adding request to fi->queued_writes and calling
    >> fuse_flush_writepages(). And the latter, in turn, guarantees proper
    >> accounting of request in fi->writectr. Here, of course, it's crucial that we
    >> can't have concurrent fuse_set_nowrite(), as you explained. Hence, so far as
    >> fi->writectr was bumped, fuse_set_nowrite() we call after
    >> filemap_write_and_wait() would wait until all changes have gone to the
    >> server.
    > Any news about this?

    Testing updated patch revealed a problem (fsx caught data corruption).
    Then I instrumented debug version to get a cue. The debug version
    survived several days of testing, but now I discovered that that test
    setup was not fully correct. I'll re-run it now.

    Thanks,
    Maxim

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