Avoid deadlocks in geometric repacking on windows#903
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dscho merged 2 commits intomicrosoft:vfs-2.54.0from Apr 28, 2026
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At some point between Windows 10 Build 17134.1304 and Build 18363.657, the default behavior of `DeleteFileW()` was changed to use POSIX semantics (https://stackoverflow.com/a/60512798). Under those semantics, a file can be deleted even when another process holds an active `MapViewOfFile` view on it: the directory entry is removed immediately, but the underlying data persists until the last handle is closed. On older Windows versions (and Windows 10 builds before that change), `DeleteFileW()` uses legacy semantics where deletion fails outright if any process holds a file mapping. To allow testing code paths that depend on the legacy behavior, introduce a `GIT_TEST_LEGACY_DELETE` environment variable. When set, `mingw_unlink()` uses `SetFileInformationByHandle()` with `FileDispositionInfo` (the non-POSIX variant) instead of `DeleteFileW()`, forcing legacy delete semantics regardless of the Windows version. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
As is done for all the other maintenance tasks, let's release the ODB also before starting the geometric repacking. That way, the `.idx` files won't be `mmap()`ed when they are to be deleted (which does not work on Windows because you cannot delete files on that platform as long as they are kept open by a process). This regression was introduced by 9bc1518 (builtin/maintenance: introduce "geometric-repack" task, 2025-10-24), but was only noticed once geometric repacking was made the default in 452b12c (builtin/ maintenance: use "geometric" strategy by default, 2026-02-24). The fix recapitulates my work from df76ee7 (run-command: offer to close the object store before running, 2021-09-09) & friends. To guard against future regressions of this kind, add a check to `run_and_verify_geometric_pack()` in `t7900` that detects orphaned `.idx` files left behind after repacking. Contrary to interactive calls, the `git maintenance` call in that test case would _not_ block on Windows, asking whether to retry deleting that file, which is the reason why this bug was not caught earlier. Furthermore, since the default behavior of `DeleteFileW()` was changed at some point between Windows 10 Build 17134.1304 and Build 18363.657 to use POSIX semantics (see https://stackoverflow.com/a/60512798), the added orphaned-`.idx` check would be insufficient to catch this regression on modern Windows without emulating legacy delete semantics via `GIT_TEST_LEGACY_DELETE=1`. This fixes git-for-windows#6210. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
derrickstolee
approved these changes
Apr 28, 2026
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This is a companion of gitgitgadget#2103 and of git-for-windows#6215.
On Windows,
maintenance_task_geometric_repack()opens pack index files viapack_geometry_init()(whichmmap()s the.idxfiles), then spawnsgit repackas a child process without settingchild.odb_to_close. The parent'smmap()s prevent the child from deleting old.idxfiles.On Windows 10 builds before the POSIX delete semantics change (between Build 17134.1304 and 18363.657, see https://stackoverflow.com/a/60512798), this results in
Unlink of file '.git/objects/pack/pack-<hash>.idx' failed. Should I try again?during fetch-triggered auto-maintenance with the geometric strategy.The fix adds the missing
child.odb_to_close = the_repository->objectsline, matching all other maintenance tasks.The first commit introduces a
GIT_TEST_LEGACY_DELETEenvironment variable to simulate legacy (pre-POSIX) delete semantics on modern Windows, so the regression test can verify the fix even on Windows 11.