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Re: [PATCH v6 02/42] refs.c: allow passing NULL to ref_transaction_free

From
Jonathan Nieder <jrnieder@gmail.com>
Date
May 13, 2014, 22:44 UTC
Message-ID
<20140513224422.GX9218@google.com>
In-Reply-To
<1398976662-6962-3-git-send-email-sahlberg@google.com>
Ronnie Sahlberg wrote:
> Allow ref_transaction_free to be called with NULL and in extension allow
> ref_transaction_rollback to be called for a NULL transaction.
In extension = as a result?
Makes sense.  It lets someone do the usual
	struct ref_transaction *transaction;
	int ret = 0;
	if (something_fails()) {
		ret = -1;
		goto cleanup;
	}
	...
 cleanup:
	ref_transaction_free(transaction);
	return ret;
just like you can already do with free().
Show 8 quoted lines
> This allows us to write code that will
>
>   if ( (!transaction ||
>         ref_transaction_update(...))  ||
>       (ref_transaction_commit(...) && !(transaction = NULL)) {
>           ref_transaction_rollback(transaction);
>           ...
>   }
Somewhere in the whitespace and parentheses I'm lost.

Is the idea that when ref_transaction_commit fails it will have freed the transaction so we need not to roll back to prevent a double free? I think it would be simpler for the caller to unconditionally set transaction to NULL after calling ref_transaction_commit in such a case to avoid use-after-free.

Even better if it is the caller's responsibility to free the transaction. At any rate, it doesn't seem related to this patch.

Show 8 quoted lines
> --- a/refs.c
> +++ b/refs.c
> @@ -3303,6 +3303,9 @@ static void ref_transaction_free(struct ref_transaction *transaction)
>  {
>  	int i;
>  
> +	if (!transaction)
> +		return;
Except for the unclear commit message,
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Previous: Ronnie SahlbergNext: Ronnie Sahlberg
Message 4 of 78 in “Use ref transactions for all ref updates”
  1. 00/42 Use ref transactions for all ref updatesRonnie Sahlberg, May 1, 2014
  2. 01/42 refs.c: constify the sha arguments for ref_transaction_create|delete|updateRonnie Sahlberg, May 1, 2014
  3. 02/42 refs.c: allow passing NULL to ref_transaction_freeRonnie Sahlberg, May 1, 2014
  4. Jonathan NiederMay 13, 2014
  5. Ronnie SahlbergMay 13, 2014
  6. Ronnie SahlbergMay 14, 2014
  7. 03/42 refs.c: add a strbuf argument to ref_transaction_commit for error loggingRonnie Sahlberg, May 1, 2014
  8. Jonathan NiederMay 13, 2014
  9. Ronnie SahlbergMay 14, 2014
  10. 04/42 refs.c: make ref_update_reject_duplicates take a strbuf argument for errorsRonnie Sahlberg, May 1, 2014
  11. Jonathan NiederMay 14, 2014
  12. Ronnie SahlbergMay 14, 2014
  13. 05/42 update-ref.c: log transaction error from the update_refRonnie Sahlberg, May 1, 2014
  14. Jonathan NiederMay 14, 2014
  15. Ronnie SahlbergMay 15, 2014
  16. 06/42 refs.c: make update_ref_write update a strbuf on failureRonnie Sahlberg, May 1, 2014
  17. Jonathan NiederMay 14, 2014
  18. 07/42 refs.c: remove the onerr argument to ref_transaction_commitRonnie Sahlberg, May 1, 2014
  19. Jonathan NiederMay 14, 2014
  20. 08/42 refs.c: change ref_transaction_update() to do error checking and return statusRonnie Sahlberg, May 1, 2014
  21. Michael HaggertyMay 5, 2014
  22. Ronnie SahlbergMay 5, 2014
  23. Jonathan NiederMay 14, 2014
  24. Ronnie SahlbergMay 15, 2014
  25. 09/42 refs.c: change ref_transaction_create to do error checking and return statusRonnie Sahlberg, May 1, 2014
  26. Jonathan NiederMay 15, 2014
  27. Ronnie SahlbergMay 15, 2014
  28. Jonathan NiederMay 15, 2014
  29. 10/42 refs.c: ref_transaction_delete to check for error and return statusRonnie Sahlberg, May 1, 2014
  30. Jonathan NiederMay 15, 2014
  31. Ronnie SahlbergMay 15, 2014
  32. 11/42 tag.c: use ref transactions when doing updatesRonnie Sahlberg, May 1, 2014
  33. Jonathan NiederMay 15, 2014
  34. Ronnie SahlbergMay 15, 2014
  35. Jonathan NiederMay 15, 2014
  36. 12/42 replace.c: use the ref transaction functions for updatesRonnie Sahlberg, May 1, 2014
  37. Jonathan NiederMay 15, 2014
  38. Ronnie SahlbergMay 15, 2014
  39. 13/42 commit.c: use ref transactions for updatesRonnie Sahlberg, May 1, 2014
  40. Jonathan NiederMay 15, 2014
  41. Ronnie SahlbergMay 15, 2014
  42. 14/42 sequencer.c: use ref transactions for all ref updatesRonnie Sahlberg, May 1, 2014
  43. Jonathan NiederMay 15, 2014
  44. 15/42 fast-import.c: change update_branch to use ref transactionsRonnie Sahlberg, May 1, 2014
  45. 16/42 branch.c: use ref transaction for all ref updatesRonnie Sahlberg, May 1, 2014
  46. 17/42 refs.c: change update_ref to use a transactionRonnie Sahlberg, May 1, 2014
  47. 18/42 refs.c: free the transaction before returning when number of updates is 0Ronnie Sahlberg, May 1, 2014
  48. 19/42 refs.c: ref_transaction_commit should not free the transactionRonnie Sahlberg, May 1, 2014
  49. 20/42 fetch.c: clear errno before calling functions that might set itRonnie Sahlberg, May 1, 2014
  50. Eric SunshineMay 2, 2014
  51. Ronnie SahlbergMay 2, 2014
  52. 21/42 fetch.c: change s_update_ref to use a ref transactionRonnie Sahlberg, May 1, 2014
  53. 22/42 fetch.c: use a single ref transaction for all ref updatesRonnie Sahlberg, May 1, 2014
  54. 23/42 receive-pack.c: use a reference transaction for updating the refsRonnie Sahlberg, May 1, 2014
  55. 24/42 fast-import.c: use a ref transaction when dumping tagsRonnie Sahlberg, May 1, 2014
  56. 25/42 walker.c: use ref transaction for ref updatesRonnie Sahlberg, May 1, 2014
  57. 26/42 refs.c: make write_ref_sha1 staticRonnie Sahlberg, May 1, 2014
  58. 27/42 refs.c: make lock_ref_sha1 staticRonnie Sahlberg, May 1, 2014
  59. 28/42 refs.c: add transaction.status and track OPEN/CLOSED/ERRORRonnie Sahlberg, May 1, 2014
  60. 29/42 refs.c: remove the update_ref_lock functionRonnie Sahlberg, May 1, 2014
  61. 30/42 refs.c: remove the update_ref_write functionRonnie Sahlberg, May 1, 2014
  62. 31/42 refs.c: remove lock_ref_sha1Ronnie Sahlberg, May 1, 2014
  63. 32/42 refs.c: make prune_ref use a transaction to delete the refRonnie Sahlberg, May 1, 2014
  64. 33/42 refs.c: make delete_ref use a transactionRonnie Sahlberg, May 1, 2014
  65. 34/42 refs.c: pass the ref log message to _create/delete/update instead of _commitRonnie Sahlberg, May 1, 2014
  66. 35/42 refs.c: pass NULL as *flags to read_ref_fullRonnie Sahlberg, May 1, 2014
  67. 36/42 refs.c: pack all refs before we start to rename a refRonnie Sahlberg, May 1, 2014
  68. 37/42 refs.c: move the check for valid refname to lock_ref_sha1_basicRonnie Sahlberg, May 1, 2014
  69. 38/42 refs.c: call lock_ref_sha1_basic directly from commitRonnie Sahlberg, May 1, 2014
  70. 39/42 refs.c: add a new flag for transaction delete for refs we know are packed onlyRonnie Sahlberg, May 1, 2014
  71. 40/42 refs.c: pass a skip list to name_conflict_fnRonnie Sahlberg, May 1, 2014
  72. Eric SunshineMay 2, 2014
  73. Ronnie SahlbergMay 2, 2014
  74. 41/42 refs.c: make rename_ref use a transactionRonnie Sahlberg, May 1, 2014
  75. 42/42 refs.c: remove forward declaraion of write_ref_sha1Ronnie Sahlberg, May 1, 2014
  76. Michael HaggertyMay 5, 2014
  77. Ronnie SahlbergMay 5, 2014
  78. Jonathan NiederMay 13, 2014

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