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Re: [PATCH 1/5] fetch-pack: sort incoming heads

From
Jeff King <peff@peff.net>
Date
May 22, 2012, 20:23 UTC
Message-ID
<20120522202336.GA31231@sigill.intra.peff.net>
In-Reply-To
<7v7gw43rn9.fsf@alter.siamese.dyndns.org>
On Tue, May 22, 2012 at 01:08:42PM -0700, Junio C Hamano wrote:
Show 11 quoted lines
> > @@ -1076,6 +1081,8 @@ struct ref *fetch_pack(struct fetch_pack_args *my_args,
> >  			st.st_mtime = 0;
> >  	}
> >  
> > +	qsort(heads, nr_heads, sizeof(*heads), compare_heads);
> > +
> >  	if (heads && nr_heads)
> >  		nr_heads = remove_duplicates(nr_heads, heads);
> 
> Hrm, could heads and/or nr_heads be NULL/0 here when we try to run qsort()
> in this codepath?

Good catch. I had originally put the qsort into remove_duplicates, but hoisted it out, as the second optimization depends on the sorting, too. heads can be NULL here (for example, if you run fetch-pack without any arguments, and without --stdin; though why you would do so is a mystery, we should protect against it).

A sane qsort would see that its second parameter is 0 and never try to dereference the array. But I'm not sure all qsort implementations we will see are sane, so it's probably better to protect it by putting it inside the conditional block just below.

-Peff
Previous: Junio C HamanoNext: Jeff King
Message 8 of 46 in “remove_duplicates() in builtin/fetch-pack.c is O(N^2)”
  1. Michael HaggertyMay 21, 2012
  2. Junio C HamanoMay 21, 2012
  3. demerphqMay 21, 2012
  4. Jeff KingMay 21, 2012
  5. Jeff KingMay 21, 2012
  6. 1/5 fetch-pack: sort incoming headsJeff King, May 21, 2012
  7. Junio C HamanoMay 22, 2012
  8. Jeff KingMay 22, 2012
  9. Jeff KingMay 24, 2012
  10. 2/5 fetch-pack: avoid quadratic behavior in remove_duplicatesJeff King, May 21, 2012
  11. 3/5 add sorting infrastructure for list refsJeff King, May 21, 2012
  12. 4/5 fetch-pack: sort the list of incoming refsJeff King, May 21, 2012
  13. 5/5 fetch-pack: avoid quadratic loop in filter_refsJeff King, May 21, 2012
  14. Junio C HamanoMay 22, 2012
  15. Jeff KingMay 21, 2012
  16. Jeff KingMay 22, 2012
  17. Michael HaggertyMay 22, 2012
  18. Jeff KingMay 22, 2012
  19. Michael HaggertyMay 22, 2012
  20. Jeff KingMay 22, 2012
  21. Michael HaggertyMay 22, 2012
  22. Jeff KingMay 22, 2012
  23. Michael HaggertyMay 24, 2012
  24. Martin FickMay 25, 2012
  25. Jeff KingMay 25, 2012
  26. Martin FickMay 25, 2012
  27. Jeff KingMay 25, 2012
  28. Martin FickMay 25, 2012
  29. Jeff KingMay 25, 2012
  30. Nguyen Thai Ngoc DuyMay 22, 2012
  31. Michael HaggertyMay 22, 2012
  32. Jeff KingMay 22, 2012
  33. Junio C HamanoMay 22, 2012
  34. Jeff KingMay 22, 2012
  35. Michael HaggertyMay 24, 2012
  36. Nguyen Thai Ngoc DuyMay 23, 2012
  37. Junio C HamanoMay 22, 2012
  38. Martin FickMay 21, 2012
  39. Jeff KingMay 21, 2012
  40. Junio C HamanoMay 21, 2012
  41. Jeff KingMay 21, 2012
  42. Martin FickMay 22, 2012
  43. Jeff KingMay 22, 2012
  44. Martin FickMay 22, 2012
  45. Junio C HamanoMay 22, 2012
  46. Martin FickMay 23, 2012

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