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[7/6] split-index: BUG() when cache entry refers to non-existing shared entry

Message ID 20181011095357.19061-1-szeder.dev@gmail.com (mailing list archive)
State New, archived
Headers show
Series Fix the racy split index problem | expand

Commit Message

SZEDER Gábor Oct. 11, 2018, 9:53 a.m. UTC
When the split index feature is in use, then a cache entry is:

  - either only present in the split index, in which case its 'index'
    field must be 0,

  - or it should refer to an existing entry in the shared index, i.e.
    the 'index' field can't be greater than the size of the shared

If a cache entry were to refer to a non-existing entry in the shared
index, then that's a sign of something being wrong in the index state,
either as a result of a bug in dealing with the split/shared index
entries, or perhaps a (potentially unrelated) memory corruption issue.

prepare_to_write_split_index() already has a condition to catch cache
entries with such bogus 'index' field, but instead of calling BUG() it
just sets cache entry's 'index = 0', and the entry will then be
written to the new split index.

Don't write a new index file from bogus index state, and call BUG()
upon encountering an cache entry referring to a non-existing shared
index entry.

Running the test suite repeatedly with 'GIT_TEST_SPLIT_INDEX=yes'
doesn't trigger this condition.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>

A follow-up to:


 split-index.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/split-index.c b/split-index.c
index 875f538802..5820412dc5 100644
--- a/split-index.c
+++ b/split-index.c
@@ -254,8 +254,8 @@  void prepare_to_write_split_index(struct index_state *istate)
 			if (ce->index > si->base->cache_nr) {
-				ce->index = 0;
-				continue;
+				BUG("ce refers to a shared ce at %d, which is beyond the shared index size %d",
+				    ce->index, si->base->cache_nr);
 			ce->ce_flags |= CE_MATCHED; /* or "shared" */
 			base = si->base->cache[ce->index - 1];