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Re: Protecting old temporary objects being reused from concurrent "git gc"?

From
Jeff King <peff@peff.net>
Date
Nov 16, 2016, 08:07 UTC
Message-ID
<20161116080753.gkn6v7vhdbifpubn@sigill.intra.peff.net>
In-Reply-To
<xmqqk2c4tsv4.fsf@gitster.mtv.corp.google.com>
On Tue, Nov 15, 2016 at 12:01:35PM -0800, Junio C Hamano wrote:
Show 15 quoted lines
> Jeff King <peff@peff.net> writes:
> 
> > I suspect the issue is that read-tree populates the cache-tree index
> > extension, and then write-tree omits the object write before it even
> > gets to write_sha1_file(). The solution is that it should probably be
> > calling one of the freshen() functions (possibly just replacing
> > has_sha1_file() with check_and_freshen(), but I haven't looked).
> 
> I think the final writing always happens via write_sha1_file(), but
> an earlier cache-tree update that says "if we have a tree object
> already, then use it, otherwise even though we know the object name
> for this subtree, do not record it in the cache-tree" codepath may
> decide to record the subtree's sha1 without refreshing the referent.
> 
> A fix may look like this.

Yeah, that's along the lines I was expecting, though I'm not familiar enough with cache-tree to say whether it's sufficient. I notice there is a return very early on in update_one() when has_sha1_file() matches, and it seems like that would trigger in some interesting cases, too.

-Peff
Previous: Junio C HamanoNext: Junio C Hamano
Message 8 of 13 in “Protecting old temporary objects being reused from concurrent "git gc"?”
  1. Matt McCutchenNov 15, 2016
  2. Jeff KingNov 15, 2016
  3. Matt McCutchenNov 15, 2016
  4. Jeff KingNov 15, 2016
  5. git-gc.txt: expand discussion of races with other processesMatt McCutchen, Nov 15, 2016
  6. Matt McCutchenNov 15, 2016
  7. Junio C HamanoNov 15, 2016
  8. Jeff KingNov 16, 2016
  9. Junio C HamanoNov 16, 2016
  10. Junio C HamanoNov 16, 2016
  11. Jeff KingNov 17, 2016
  12. Re* Protecting old temporary objects being reused from concurrent "git gc"?Junio C Hamano, Nov 17, 2016
  13. Jeff KingNov 17, 2016

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