From: Ben Peart <peartben@gmail.com>
To: Junio C Hamano <gitster@pobox.com>, Ben Peart <benpeart@microsoft.com>
Cc: git@vger.kernel.org, pclouds@gmail.com, blees@dcon.de
Subject: Re: [PATCH v1] Fix bugs preventing adding updated cache entries to the name hash
Date: Thu, 15 Mar 2018 14:44:06 -0400 [thread overview]
Message-ID: <339cd7f7-9ca0-62cf-ea46-588be119eedd@gmail.com> (raw)
In-Reply-To: <xmqqfu515ihj.fsf@gitster-ct.c.googlers.com>
On 3/15/2018 1:58 PM, Junio C Hamano wrote:
> Ben Peart <benpeart@microsoft.com> 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.
>
next prev parent reply other threads:[~2018-03-15 18:44 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-15 15:25 [PATCH v1] Fix bugs preventing adding updated cache entries to the name hash Ben Peart
2018-03-15 17:58 ` Junio C Hamano
2018-03-15 18:44 ` Ben Peart [this message]
2018-03-15 18:58 ` Junio C Hamano
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