Fix racy fsmonitor #223
Fix racy fsmonitor #223
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We will need to pass down the `struct index_state` to `mark_fsmonitor_valid()` for an upcoming bug fix, and this here function calls that there function, so we need to extend the signature of `fill_stat_cache_info()` first. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Without this bug fix, t7519's four "status doesn't detect unreported modifications" test cases would fail occasionally (and, oddly enough, *a lot* more frequently on Windows). The reason is that these test cases intentionally use the side effect of `git status` to re-write the index if any updates were detected: they first clean the worktree, run `git status` to update the index as well as show the output to the casual reader, then make the worktree dirty again and expect no changes to reported if running with a mocked fsmonitor hook. The problem with this strategy was that the index was written during said `git status` on the clean worktree for the *wrong* reason: not because the index was marked as changed (it wasn't), but because the recorded mtimes were racy with the index' own mtime. As the mtime granularity on Windows is 100 nanoseconds (see e.g. https://docs.microsoft.com/en-us/windows/desktop/SysInfo/file-times), the mtimes of the files are often enough *not* racy with the index', so that that `git status` call currently does not always update the index (including the fsmonitor extension), causing the test case to fail. The obvious fix: if we change *any* index entry's `CE_FSMONITOR_VALID` flag, we should also mark the index as changed. That will cause the index to be written upon `git status`, *including* an updated fsmonitor extension. Side note: Even though the reader might think that the t7519 issue should be *much* more prevalent on Linux, given that the ext4 filesystem (that seems to be used by every Linux distribution) stores mtimes in nanosecond precision. However, ext4 uses `current_kernel_time()` (see https://unix.stackexchange.com/questions/11599#comment762968_11599; it is *amazingly* hard to find any proper source of information about such ext4 questions) whose accuracy seems to depend on many factors but is safely worse than the 100-nanosecond granularity of NTFS (again, it is *horribly* hard to find anything remotely authoritative about this question). So it seems that the racy index condition that hid the bug fixed by this patch simply is a lot more likely on Linux than on Windows. But not impossible ;-) Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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Submitted as pull.223.git.gitgitgadget@gmail.com |
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This patch series was integrated into pu via git@51e7b33. |
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This patch series was integrated into pu via git@a3e6b42. |
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This patch series was integrated into next via git@a3e6b42. |
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This patch series was integrated into master via git@a3e6b42. |
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Closed via a3e6b42. |
The
t7519-status-fsmonitor.shtests became a lot more flaky with the recent fsmonitor fix (js/fsmonitor-refresh-after-discarding-index). That fix, however, did not introduce the flakiness, but it just made it much more likely to be hit. And it seemed to be hit only on Windows.The reason, though, is that the fsmonitor feature failed to mark the in-memory index as changed, i.e. in need of writing, and it was the
has_racy_timestamp()test that hid this bug in most cases (although a lot less on Windows, where the files' mtimes are actually a lot more accurate than on Linux).This fixes #197
Cc: Ævar Arnfjörð Bjarmason avarab@gmail.com