Re: [PATCH 1/3] builtin/commit-graph.c: support '--split[=<strategy>]'

> On Thu, Jan 30, 2020 at 04:28:17PM -0800, Taylor Blau wrote:
> > diff --git a/commit-graph.c b/commit-graph.c
> > index 6d34829f57..02e6ad9d1f 100644
> > --- a/commit-graph.c
> > +++ b/commit-graph.c
> > @@ -1565,15 +1565,18 @@ static void split_graph_merge_strategy(struct write_commit_graph_context *ctx)
> >  	num_commits = ctx->commits.nr;
> >  	ctx->num_commit_graphs_after = ctx->num_commit_graphs_before + 1;
> >
> > -	while (g && (g->num_commits <= size_mult * num_commits ||
> > -		    (max_commits && num_commits > max_commits))) {
> > -		if (g->odb != ctx->odb)
> > -			break;
> > +	if (ctx->split_opts->flags != COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED) {
>
> This line segfaults in the tests 'fetch.writeCommitGraph' and
> 'fetch.writeCommitGraph with submodules' in 't5510-fetch.sh', because
> 'git fetch' doesn't pass a 'split_opts' to the commit-graph functions.

> Thread 1 "git" received signal SIGSEGV, Segmentation fault.
> 0x00000000005113dd in split_graph_merge_strategy (ctx=0x9ca930)
>     at commit-graph.c:1568
> 1568            if (ctx->split_opts->flags != COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED) {
> (gdb) p *ctx
> $1 = {r = 0x9ae2a0 <the_repo>, odb = 0x9c0df0, graph_name = 0x0, oids = {
>     list = 0xa02660, nr = 12, alloc = 1024}, commits = {list = 0x9caa00,
>     nr = 6, alloc = 6}, num_extra_edges = 0, approx_nr_objects = 0,
>   progress = 0x0, progress_done = 0, progress_cnt = 0, base_graph_name = 0x0,
>   num_commit_graphs_before = 0, num_commit_graphs_after = 1,
>   commit_graph_filenames_before = 0x0, commit_graph_filenames_after = 0x0,
>   commit_graph_hash_after = 0x0, new_num_commits_in_base = 0,
>   new_base_graph = 0x0, append = 0, report_progress = 1, split = 1,
>   check_oids = 0, split_opts = 0x0}
>                   ^^^^^^^^^^^^^^^^
> (gdb) bt
> #0  0x00000000005113dd in split_graph_merge_strategy (ctx=0x9ca930)
>     at commit-graph.c:1568
> #1  0x0000000000512446 in write_commit_graph (odb=0x9c0df0, pack_indexes=0x0,
>     commit_hex=0x7fffffffd550,
>     flags=(COMMIT_GRAPH_WRITE_PROGRESS | COMMIT_GRAPH_WRITE_SPLIT),
>     split_opts=0x0) at commit-graph.c:1891
> #2  0x000000000050fd86 in write_commit_graph_reachable (odb=0x9c0df0,
>     flags=(COMMIT_GRAPH_WRITE_PROGRESS | COMMIT_GRAPH_WRITE_SPLIT),
>     split_opts=0x0) at commit-graph.c:1174
>     ^^^^^^^^^^^^^^
> #3  0x0000000000444ea4 in cmd_fetch (argc=0, argv=0x7fffffffd9b8, prefix=0x0)
>     at builtin/fetch.c:1873
> #4  0x0000000000406154 in run_builtin (p=0x969a88 <commands+840>, argc=2,
>     argv=0x7fffffffd9b0) at git.c:444
> #5  0x00000000004064a4 in handle_builtin (argc=2, argv=0x7fffffffd9b0)
>     at git.c:674
> #6  0x000000000040674c in run_argv (argcp=0x7fffffffd84c, argv=0x7fffffffd840)
>     at git.c:741
> #7  0x0000000000406bbd in cmd_main (argc=2, argv=0x7fffffffd9b0) at git.c:872
> #8  0x00000000004cfd4e in main (argc=5, argv=0x7fffffffd998)
>     at common-main.c:52
>
> Note that this function split_graph_merge_strategy() does look at
> various fields in 'ctx->split_opts' a bit earlier, but those accesses
> are protected by a 'if (ctx->split_opts)' condition.
> expire_commit_graphs() does the same.
>
>
> > +		while (g && (g->num_commits <= size_mult * num_commits ||
> > +			    (max_commits && num_commits > max_commits) ||
> > +			    (ctx->split_opts->flags == COMMIT_GRAPH_SPLIT_MERGE_REQUIRED))) {
> > +			if (g->odb != ctx->odb)
> > +				break;
> >
> > -		num_commits += g->num_commits;
> > -		g = g->base_graph;
> > +			num_commits += g->num_commits;
> > +			g = g->base_graph;
> >
> > -		ctx->num_commit_graphs_after--;
> > +			ctx->num_commit_graphs_after--;
> > +		}
> >  	}
> >