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git tag --contains: avoid stack overflow 

In large repos, the recursion implementation of contains(commit,
commit_list) may result in a stack overflow. Replace the recursion with
a loop to fix it.

This problem is more apparent on Windows than on Linux, where the stack
is more limited by default.

See also this thread on the msysGit list:

	https://groups.google.com/d/topic/msysgit/FqT6boJrb2g/discussion

[jes: re-written to imitate the original recursion more closely]

Thomas Braun pointed out several documentation shortcomings.

Tests are run only if ulimit -s is available.  This means they cannot
be run on Windows.

Signed-off-by: Jean-Jacques Lafay <jeanjacques.lafay@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Tested-by: Stepan Kasal <kasal@ucw.cz>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jean-Jacques Lafay 2014-04-24 14:24:39 +02:00 committed by Junio C Hamano
parent 779792a5f2
commit cbc60b6720
2 changed files with 101 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

90
builtin/tag.c
View File

@ -80,11 +80,19 @@ static int in_commit_list(const struct commit_list *want, struct commit *c)
return 0;
}
static int contains_recurse(struct commit *candidate,
enum contains_result {
CONTAINS_UNKNOWN = -1,
CONTAINS_NO = 0,
CONTAINS_YES = 1,
};
/*
* Test whether the candidate or one of its parents is contained in the list.
* Do not recurse to find out, though, but return -1 if inconclusive.
*/
static enum contains_result contains_test(struct commit *candidate,
const struct commit_list *want)
{
struct commit_list *p;
/* was it previously marked as containing a want commit? */
if (candidate->object.flags & TMP_MARK)
return 1;
@ -92,26 +100,78 @@ static int contains_recurse(struct commit *candidate,
if (candidate->object.flags & UNINTERESTING)
return 0;
/* or are we it? */
if (in_commit_list(want, candidate))
if (in_commit_list(want, candidate)) {
candidate->object.flags |= TMP_MARK;
return 1;
}
if (parse_commit(candidate) < 0)
return 0;
/* Otherwise recurse and mark ourselves for future traversals. */
for (p = candidate->parents; p; p = p->next) {
if (contains_recurse(p->item, want)) {
candidate->object.flags |= TMP_MARK;
return 1;
}
}
candidate->object.flags |= UNINTERESTING;
return 0;
return -1;
}
static int contains(struct commit *candidate, const struct commit_list *want)
/*
* Mimicking the real stack, this stack lives on the heap, avoiding stack
* overflows.
*
* At each recursion step, the stack items points to the commits whose
* ancestors are to be inspected.
*/
struct stack {
int nr, alloc;
struct stack_entry {
struct commit *commit;
struct commit_list *parents;
} *stack;
};
static void push_to_stack(struct commit *candidate, struct stack *stack)
{
return contains_recurse(candidate, want);
int index = stack->nr++;
ALLOC_GROW(stack->stack, stack->nr, stack->alloc);
stack->stack[index].commit = candidate;
stack->stack[index].parents = candidate->parents;
}
static enum contains_result contains(struct commit *candidate,
const struct commit_list *want)
{
struct stack stack = { 0, 0, NULL };
int result = contains_test(candidate, want);
if (result != CONTAINS_UNKNOWN)
return result;
push_to_stack(candidate, &stack);
while (stack.nr) {
struct stack_entry *entry = &stack.stack[stack.nr - 1];
struct commit *commit = entry->commit;
struct commit_list *parents = entry->parents;
if (!parents) {
commit->object.flags |= UNINTERESTING;
stack.nr--;
}
/*
* If we just popped the stack, parents->item has been marked,
* therefore contains_test will return a meaningful 0 or 1.
*/
else switch (contains_test(parents->item, want)) {
case CONTAINS_YES:
commit->object.flags |= TMP_MARK;
stack.nr--;
break;
case CONTAINS_NO:
entry->parents = parents->next;
break;
case CONTAINS_UNKNOWN:
push_to_stack(parents->item, &stack);
break;
}
}
free(stack.stack);
return contains_test(candidate, want);
}
static void show_tag_lines(const unsigned char *sha1, int lines)

26
t/t7004-tag.sh
View File

@ -1423,4 +1423,30 @@ EOF
test_cmp expect actual
'
run_with_limited_stack () {
(ulimit -s 64 && "$@")
}
test_lazy_prereq ULIMIT 'run_with_limited_stack true'
# we require ulimit, this excludes Windows
test_expect_success ULIMIT '--contains works in a deep repo' '
>expect &&
i=1 &&
while test $i -lt 4000
do
echo "commit refs/heads/master
committer A U Thor <author@example.com> $((1000000000 + $i * 100)) +0200
data <<EOF
commit #$i
EOF"
test $i = 1 && echo "from refs/heads/master^0"
i=$(($i + 1))
done | git fast-import &&
git checkout master &&
git tag far-far-away HEAD^ &&
run_with_limited_stack git tag --contains HEAD >actual &&
test_cmp expect actual
'
test_done