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

From: Taylor Blau <me@ttaylorr.com>
To: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Cc: "SZEDER Gábor" <szeder.dev@gmail.com>,
	"Taylor Blau" <me@ttaylorr.com>,
	git@vger.kernel.org, peff@peff.net, dstolee@microsoft.com,
	gitster@pobox.com
Subject: Re: [PATCH 1/3] builtin/commit-graph.c: support '--split[=<strategy>]'
Date: Mon, 3 Feb 2020 19:59:40 -0800	[thread overview]
Message-ID: <20200204035940.GD5790@syl.local> (raw)
In-Reply-To: <nycvar.QRO.7.76.6.2002012223490.46@tvgsbejvaqbjf.bet>

On Sat, Feb 01, 2020 at 10:25:36PM +0100, Johannes Schindelin wrote:
> Hi,
>
> On Sat, 1 Feb 2020, SZEDER Gábor wrote:
>
> > 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.
>
> I noticed the same. This patch seems to fix it for me:
>
> -- snip --
> diff --git a/commit-graph.c b/commit-graph.c
> index a5d7624073f..af5c58833cf 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -1566,7 +1566,8 @@ 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;
>
> -	if (ctx->split_opts->flags != COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED) {
> +	if (ctx->split_opts &&
> +	    ctx->split_opts->flags != COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED) {
>  		while (g && (g->num_commits <= size_mult * num_commits ||
>  			    (max_commits && num_commits > max_commits) ||
>  			    (ctx->split_opts->flags == COMMIT_GRAPH_SPLIT_MERGE_REQUIRED))) {
> -- snap --
>
> For your convenience, I also pushed this up as
> `tb/commit-graph-split-merge` to https://github.com/dscho/git

Thanks, Dscho. I also published it under the same name on my fork at
'https://github.com/ttaylorr/git'.

> Thanks,
> Dscho
>
>
> >
> > 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--;
> > > +		}
> > >  	}
> > >
> >

Thanks,
Taylor