builtin/maintenance: fix locking race when handling "gc" task
The "gc" task has a similar locking race as the one that we have fixed for the "pack-refs" and "reflog-expire" tasks in preceding commits. Fix this by splitting up the logic of the "gc" task: - We execute `gc_before_repack()` in the foreground, which contains the logic that git-gc(1) itself would execute in the foreground, as well. - We spawn git-gc(1) after detaching, but with a new hidden flag that suppresses calling `gc_before_repack()`. Like this we have roughly the same logic as git-gc(1) itself and know to repack refs and reflogs before detaching, thus fixing the race. Note that `gc_before_repack()` is renamed to `gc_foreground_tasks()` to better reflect what this function does. Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Patrick Steinhardt committed
Jun 3, 2025 at 16:01 UTC
1b5074e614d9b32bd760d2583e7435685ca4faab
2 files changed
+33
-20
builtin/gc.c
+27
-14
@@ -816,8 +816,8 @@ done:
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return ret;
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}
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-static int gc_before_repack(struct maintenance_run_opts *opts,
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- struct gc_config *cfg)
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+static int gc_foreground_tasks(struct maintenance_run_opts *opts,
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+ struct gc_config *cfg)
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{
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if (cfg->pack_refs && maintenance_task_pack_refs(opts, cfg))
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return error(FAILED_RUN, "pack-refs");
@@ -837,6 +837,7 @@ int cmd_gc(int argc,
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pid_t pid;
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int daemonized = 0;
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int keep_largest_pack = -1;
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+ int skip_foreground_tasks = 0;
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timestamp_t dummy;
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struct maintenance_run_opts opts = MAINTENANCE_RUN_OPTS_INIT;
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struct gc_config cfg = GC_CONFIG_INIT;
@@ -869,6 +870,8 @@ int cmd_gc(int argc,
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N_("repack all other packs except the largest pack")),
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OPT_STRING(0, "expire-to", &cfg.repack_expire_to, N_("dir"),
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N_("pack prefix to store a pack containing pruned objects")),
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+ OPT_HIDDEN_BOOL(0, "skip-foreground-tasks", &skip_foreground_tasks,
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+ N_("skip maintenance tasks typically done in the foreground")),
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OPT_END()
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};
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@@ -952,14 +955,16 @@ int cmd_gc(int argc,
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goto out;
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}
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- if (lock_repo_for_gc(force, &pid)) {
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- ret = 0;
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- goto out;
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- }
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+ if (!skip_foreground_tasks) {
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+ if (lock_repo_for_gc(force, &pid)) {
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+ ret = 0;
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+ goto out;
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+ }
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- if (gc_before_repack(&opts, &cfg) < 0)
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- die(NULL);
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- delete_tempfile(&pidfile);
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+ if (gc_foreground_tasks(&opts, &cfg) < 0)
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+ die(NULL);
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+ delete_tempfile(&pidfile);
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+ }
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/*
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* failure to daemonize is ok, we'll continue
@@ -988,8 +993,8 @@ int cmd_gc(int argc,
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free(path);
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}
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- if (opts.detach <= 0)
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- gc_before_repack(&opts, &cfg);
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+ if (opts.detach <= 0 && !skip_foreground_tasks)
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+ gc_foreground_tasks(&opts, &cfg);
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if (!repository_format_precious_objects) {
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struct child_process repack_cmd = CHILD_PROCESS_INIT;
@@ -1225,8 +1230,14 @@ static int maintenance_task_prefetch(struct maintenance_run_opts *opts,
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return 0;
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}
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-static int maintenance_task_gc(struct maintenance_run_opts *opts,
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- struct gc_config *cfg UNUSED)
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+static int maintenance_task_gc_foreground(struct maintenance_run_opts *opts,
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+ struct gc_config *cfg)
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+{
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+ return gc_foreground_tasks(opts, cfg);
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+}
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+
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+static int maintenance_task_gc_background(struct maintenance_run_opts *opts,
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+ struct gc_config *cfg UNUSED)
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{
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struct child_process child = CHILD_PROCESS_INIT;
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@@ -1240,6 +1251,7 @@ static int maintenance_task_gc(struct maintenance_run_opts *opts,
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else
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strvec_push(&child.args, "--no-quiet");
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strvec_push(&child.args, "--no-detach");
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+ strvec_push(&child.args, "--skip-foreground-tasks");
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return run_command(&child);
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}
@@ -1571,7 +1583,8 @@ static const struct maintenance_task tasks[] = {
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},
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[TASK_GC] = {
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.name = "gc",
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- .background = maintenance_task_gc,
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+ .foreground = maintenance_task_gc_foreground,
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+ .background = maintenance_task_gc_background,
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.auto_condition = need_to_gc,
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},
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[TASK_COMMIT_GRAPH] = {
t/t7900-maintenance.sh
+6
-6
@@ -49,9 +49,9 @@ test_expect_success 'run [--auto|--quiet]' '
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git maintenance run --auto 2>/dev/null &&
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GIT_TRACE2_EVENT="$(pwd)/run-no-quiet.txt" \
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git maintenance run --no-quiet 2>/dev/null &&
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- test_subcommand git gc --quiet --no-detach <run-no-auto.txt &&
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- test_subcommand ! git gc --auto --quiet --no-detach <run-auto.txt &&
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- test_subcommand git gc --no-quiet --no-detach <run-no-quiet.txt
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+ test_subcommand git gc --quiet --no-detach --skip-foreground-tasks <run-no-auto.txt &&
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+ test_subcommand ! git gc --auto --quiet --no-detach --skip-foreground-tasks <run-auto.txt &&
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+ test_subcommand git gc --no-quiet --no-detach --skip-foreground-tasks <run-no-quiet.txt
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'
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test_expect_success 'maintenance.auto config option' '
@@ -154,9 +154,9 @@ test_expect_success 'run --task=<task>' '
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git maintenance run --task=commit-graph 2>/dev/null &&
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GIT_TRACE2_EVENT="$(pwd)/run-both.txt" \
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git maintenance run --task=commit-graph --task=gc 2>/dev/null &&
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- test_subcommand ! git gc --quiet --no-detach <run-commit-graph.txt &&
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- test_subcommand git gc --quiet --no-detach <run-gc.txt &&
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- test_subcommand git gc --quiet --no-detach <run-both.txt &&
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+ test_subcommand ! git gc --quiet --no-detach --skip-foreground-tasks <run-commit-graph.txt &&
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+ test_subcommand git gc --quiet --no-detach --skip-foreground-tasks <run-gc.txt &&
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+ test_subcommand git gc --quiet --no-detach --skip-foreground-tasks <run-both.txt &&
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test_subcommand git commit-graph write --split --reachable --no-progress <run-commit-graph.txt &&
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test_subcommand ! git commit-graph write --split --reachable --no-progress <run-gc.txt &&
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test_subcommand git commit-graph write --split --reachable --no-progress <run-both.txt