From: Derrick Stolee <derrickstolee@github.com>
To: Han Xin <hanxin.hx@bytedance.com>, git@vger.kernel.org
Cc: xingxin.xx@bytedance.com, jonathantanmy@google.com,
Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH v2 1/2] negotiator/default: avoid stack overflow
Date: Wed, 26 Apr 2023 07:13:15 -0400 [thread overview]
Message-ID: <bf45bfe7-4a29-38d6-b8d7-811581aec82b@github.com> (raw)
In-Reply-To: <935be72eb92cd2eda7aff43c8cc2306b78b2a146.1682473718.git.hanxin.hx@bytedance.com>
On 4/26/2023 12:05 AM, Han Xin wrote:
> mark_common() in negotiator/default.c may overflow the stack due to
> recursive function calls. Avoid this by instead recursing using a
> heap-allocated data structure.
>
> This is the same case as [1].
>
> 1. 4654134976f (negotiator/skipping: avoid stack overflow, 2022-10-25)
We would typically write this inline, such as:
This is the same case as 4654134976f (negotiator/skipping: avoid
stack overflow, 2022-10-25)
> - if (commit != NULL && !(commit->object.flags & COMMON)) {
> - struct object *o = (struct object *)commit;
> + struct prio_queue queue = { NULL };
> +
> + if (!commit || (commit->object.flags & COMMON))
> + return;
> +
> + prio_queue_put(&queue, commit);
> + if (!ancestors_only) {
> + commit->object.flags |= COMMON;
>
> - if (!ancestors_only)
> - o->flags |= COMMON;
> + if ((commit->object.flags & SEEN) && !(commit->object.flags & POPPED))
> + ns->non_common_revs--;
> + }
> + while ((commit = prio_queue_get(&queue))) {
> + struct object *o = (struct object *)commit;
>
> if (!(o->flags & SEEN))
> rev_list_push(ns, commit, SEEN);
> else {
> struct commit_list *parents;
>
> - if (!ancestors_only && !(o->flags & POPPED))
> - ns->non_common_revs--;
> if (!o->parsed && !dont_parse)
> if (repo_parse_commit(the_repository, commit))
> - return;
> + continue;
>
> for (parents = commit->parents;
> parents;
> - parents = parents->next)
> - mark_common(ns, parents->item, 0,
> - dont_parse);
> + parents = parents->next) {
> + struct commit *p = parents->item;
> +
> + if (p->object.flags & COMMON)
> + continue;
> +
> + p->object.flags |= COMMON;
> +
> + if ((p->object.flags & SEEN) && !(p->object.flags & POPPED))
> + ns->non_common_revs--;
> +
> + prio_queue_put(&queue, parents->item);
> + }
> }
> }
> +
> + clear_prio_queue(&queue);
Thanks for this version. It looks like an identical set of actions
in the commit walk, but the change from DFS to priority queue is
a welcome change.
-Stolee
next prev parent reply other threads:[~2023-04-26 11:13 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-24 2:23 [PATCH v1] negotiator/default.c: avoid stack overflow Han Xin
2023-04-24 14:44 ` Derrick Stolee
2023-04-25 3:02 ` [External] " Han Xin
2023-04-25 13:34 ` Derrick Stolee
2023-04-26 4:05 ` [PATCH v2 0/2] negotiator/default: " Han Xin
2023-04-26 4:05 ` [PATCH v2 1/2] " Han Xin
2023-04-26 11:13 ` Derrick Stolee [this message]
2023-04-26 11:40 ` [External] " Han Xin
2023-04-26 4:05 ` [PATCH v2 2/2] negotiator/skipping: fix some problems in mark_common() Han Xin
2023-04-26 11:08 ` Derrick Stolee
2023-04-26 11:55 ` [External] " Han Xin
2023-04-26 13:15 ` [PATCH v2 0/2] negotiator/default: avoid stack overflow Han Xin
2023-04-26 13:15 ` [PATCH v3 1/2] " Han Xin
2023-04-26 17:14 ` Junio C Hamano
2023-04-26 17:30 ` Derrick Stolee
2023-04-26 17:38 ` Junio C Hamano
2023-04-26 13:15 ` [PATCH v3 2/2] negotiator/skipping: fix some problems in mark_common() Han Xin
2023-05-01 22:11 ` [PATCH v2 0/2] negotiator/default: avoid stack overflow Junio C Hamano
2023-05-02 1:49 ` Derrick Stolee
2023-05-02 15:51 ` Junio C Hamano
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