[PATCH v5 1/3] rerere: wait for MERGE_RR.lock before giving up
- From
Thomas Bachem via GitGitGadget <gitgitgadget@gmail.com>
- Date
- Sep 28, 2026, 11:58 UTC
- Message-ID
- <3dc3d02f12a3118ac9e270c19960815f6b8170cb.1790596702.git.gitgitgadget@gmail.com>
- In-Reply-To
- <pull.2214.v5.git.1790596702.gitgitgadget@gmail.com>
From: Thomas Bachem <mail@thomasbachem.com>
setup_rerere() takes MERGE_RR.lock with LOCK_DIE_ON_ERROR, so of two processes that want it at the same time the second one dies. That used to be rare. Since 452b12c2e0 (builtin/maintenance: use "geometric" strategy by default, 2026-02-24) the auto maintenance after a commit runs "git rerere gc" whenever rr-cache has enough stale entries, and the gc holds the lock while it prunes.
A rebase whose next pick conflicts while that happens dies inside repo_rerere(), before the sequencer has written the state that "git rebase --continue" needs. Every later "git rebase --continue" then fails with "you have staged changes in your working tree".
Wait for the lock for up to rerere.lockTimeout milliseconds, 1000 by default, and only then fail as before. Pruning a few thousand entries takes well under a second, so the default covers a rebase that runs into the gc.
Assisted-by: Claude Fable 5.1 Signed-off-by: Thomas Bachem <mail@thomasbachem.com> --- Documentation/config/rerere.adoc | 8 +++++ rerere.c | 22 ++++++++++--- t/t4200-rerere.sh | 53 ++++++++++++++++++++++++++++++++ 3 files changed, 78 insertions(+), 5 deletions(-)
diff --git a/Documentation/config/rerere.adoc b/Documentation/config/rerere.adoc index 3a78b5ebb1..30e827f32b 100644 --- a/Documentation/config/rerere.adoc +++ b/Documentation/config/rerere.adoc @@ -10,3 +10,11 @@ rerere.enabled:: enabled if there is an `rr-cache` directory under the `$GIT_DIR`, e.g. if "rerere" was previously used in the repository. + +rerere.lockTimeout:: + The length of time, in milliseconds, to wait for the rerere + lock when another process holds it, typically a background + `git rerere gc`. Value 0 means not to wait at all; -1 means + to wait indefinitely. Default is 1000 (i.e., wait for 1 + second). When the time is up, the command fails as it does + for any other lock it cannot take. diff --git a/rerere.c b/rerere.c index 1c3745d9e3..64fac07c71 100644 --- a/rerere.c +++ b/rerere.c @@ -33,6 +33,9 @@ static int rerere_enabled = -1; /* automatically update cleanly resolved paths to the index */ static int rerere_autoupdate; +/* how long to wait for MERGE_RR.lock, in milliseconds */ +static int rerere_lock_timeout_ms = 1000; + #define RR_HAS_POSTIMAGE 1 #define RR_HAS_PREIMAGE 2 struct rerere_dir { @@ -850,6 +853,8 @@ static void git_rerere_config(void) { repo_config_get_bool(the_repository, "rerere.enabled", &rerere_enabled); repo_config_get_bool(the_repository, "rerere.autoupdate", &rerere_autoupdate); + repo_config_get_int(the_repository, "rerere.locktimeout", + &rerere_lock_timeout_ms); repo_config(the_repository, git_default_config, NULL); } @@ -882,12 +887,19 @@ int setup_rerere(struct repository *r, struct string_list *merge_rr, int flags) if (flags & (RERERE_AUTOUPDATE|RERERE_NOAUTOUPDATE)) rerere_autoupdate = !!(flags & RERERE_AUTOUPDATE); - if (flags & RERERE_READONLY) + if (flags & RERERE_READONLY) { fd = 0; - else - fd = repo_hold_lock_file_for_update(r, &write_lock, - git_path_merge_rr(r), - LOCK_DIE_ON_ERROR); + } else { + /* + * Another process may hold the lock for a while, e.g. + * "git rerere gc" while it prunes rr-cache, so wait for + * it instead of dying right away. + */ + fd = repo_hold_lock_file_for_update_timeout(r, &write_lock, + git_path_merge_rr(r), + LOCK_DIE_ON_ERROR, + rerere_lock_timeout_ms); + } read_rr(r, merge_rr); return fd; } diff --git a/t/t4200-rerere.sh b/t/t4200-rerere.sh index 7bb601e117..7bd92235dc 100755 --- a/t/t4200-rerere.sh +++ b/t/t4200-rerere.sh @@ -242,6 +242,59 @@ test_expect_success 'old records rest in peace' ' test_path_is_missing $rr2/preimage ' +test_expect_success 'a held lock is waited out within rerere.lockTimeout' ' + git reset --hard && + rm -rf $rr && + test_when_finished "rm -f .git/MERGE_RR.lock" && + >.git/MERGE_RR.lock && + { + ( sleep 1 && rm -f .git/MERGE_RR.lock ) & + } && + test_must_fail git -c rerere.lockTimeout=5000 merge first 2>err && + wait && + test_grep ! "MERGE_RR" err && + test_grep "^=======\$" $rr/preimage +' + +test_expect_success 'merge fails once rerere.lockTimeout is up' ' + git reset --hard && + rm -rf $rr && + test_when_finished "rm -f .git/MERGE_RR.lock" && + >.git/MERGE_RR.lock && + test_must_fail git -c rerere.lockTimeout=0 merge first 2>err && + test_grep "Unable to create" err && + test_grep "^=======\$" a1 && + test_path_is_missing $rr/preimage +' + +test_expect_success 'rerere, forget, clear and gc fail on a lock they cannot take' ' + test_when_finished "rm -f .git/MERGE_RR.lock" && + >.git/MERGE_RR.lock && + test_must_fail git -c rerere.lockTimeout=0 rerere 2>err && + test_grep "Unable to create" err && + test_must_fail git -c rerere.lockTimeout=0 rerere forget a1 2>err && + test_grep "Unable to create" err && + test_must_fail git -c rerere.lockTimeout=0 rerere clear 2>err && + test_grep "Unable to create" err && + test_must_fail git -c rerere.lockTimeout=0 rerere gc 2>err && + test_grep "Unable to create" err +' + +test_expect_success 'rebase --abort fails on a lock it cannot take' ' + git reset --hard && + git checkout -b lock-held-abort third && + test_when_finished "git checkout third && git branch -D lock-held-abort" && + test_must_fail git rebase first && + test_when_finished "rm -f .git/MERGE_RR.lock" && + >.git/MERGE_RR.lock && + test_must_fail git -c rerere.lockTimeout=0 rebase --abort 2>err && + test_grep "Unable to create" err && + test_path_is_dir .git/rebase-merge && + rm .git/MERGE_RR.lock && + git rebase --abort && + test_path_is_missing .git/rebase-merge +' + rerere_gc_custom_expiry_test () { five_days="$1" right_now="$2" test_expect_success "rerere gc with custom expiry ($five_days, $right_now)" '
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