From: Ben Peart Date: Thu, 15 Mar 2018 18:44:06 GMT Subject: Re: [PATCH v1] Fix bugs preventing adding updated cache entries to the name hash Message-ID: <339cd7f7-9ca0-62cf-ea46-588be119eedd@gmail.com> In-Reply-To: On 3/15/2018 1:58 PM, Junio C Hamano wrote: > Ben Peart writes: > >> Update replace_index_entry() to clear the CE_HASHED flag from the new cache >> entry so that it can add it to the name hash in set_index_entry() > > OK. > >> diff --git a/read-cache.c b/read-cache.c >> index 977921d90c..bdfa552861 100644 >> --- a/read-cache.c >> +++ b/read-cache.c >> @@ -62,6 +62,7 @@ static void replace_index_entry(struct index_state *istate, int nr, struct cache >> replace_index_entry_in_base(istate, old, ce); >> remove_name_hash(istate, old); >> free(old); >> + ce->ce_flags &= ~CE_HASHED; >> set_index_entry(istate, nr, ce); >> ce->ce_flags |= CE_UPDATE_IN_BASE; >> mark_fsmonitor_invalid(istate, ce); > > As we are removing "old" that is not "ce", an earlier call to > remove_name_hash() that clears the CE_HASHED bit from the cache > entry does not help us at all. We need to clear the bit from "ce" > ourselves before calling set_index_entry() on it, otherwise the call > would become a no-op wrt the name hash. Makes sense. > Correct. As you note below, this one line is sufficient to fix the actual bug. > Makes me wonder why "ce" which is a replacement for what is in the > index already has the hashed bit, though. Is that the failure to > use copy_cache_entry() in the caller the other part of this patch > fixes? To me it looks like copy_cache_entry() is designed for > copying an entry's data to another one that has a different name, > but in the refresh codepath, we _know_ we are replacing an old entry > with an entry with the same name, so it somehow feels a bit strange > to use copy_cache_entry(), instead of doing memcpy() (and possibly > dropping the HASHED bit from the new copy--but wouldn't that become > unnecessary with the fix to replace_index_entry() we saw above?) > This 2nd part of the patch was more for code cleanliness. When I was investigating why the hashed bit was set, it was caused by this memcpy(). When I examined the rest of the code base, I only found 1 other instance (in dup_entry()) that did a straight memcpy(), the rest used the copy_cache_entry() macro. I updated this code to match that pattern as it would have prevented the bug as well though as you correctly point out, it is not necessary with the other fix. > Is this fix something we can demonstrate in a new test, by the way? > Unfortunately I was unable to find a way to reliably demonstrate this bug and fix with a new test. I only ran across it while working on another patch series that ends up triggering it more reliably. The symptom was that occasionally in very specific circumstances a git status call would incorrectly show some directories as having untracked files when there were actually no untracked files in that directory. A subsequent call to status would correctly show no untracked files as would git status -uall. I do have a test for this fix as part of the other patch series but thought I'd submit this bug fix separately as it may be a while before the other patch series is ready. > Thanks. >