From: "Martin Ågren" <martin.agren@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Michael Haggerty <mhagger@alum.mit.edu>,
Git Mailing List <git@vger.kernel.org>
Subject: Re: [PATCH v3 1/3] refs/files-backend: add longer-scoped copy of string to list
Date: Tue, 5 Sep 2017 19:24:18 +0200 [thread overview]
Message-ID: <CAN0heSqnrPUEgP-BgvuHuVrDG2ifuHHDOPPmxiXJ73u4-PrOng@mail.gmail.com> (raw)
In-Reply-To: <xmqq60cxcvjk.fsf@gitster.mtv.corp.google.com>
On 5 September 2017 at 12:02, Junio C Hamano <gitster@pobox.com> wrote:
> Martin Ågren <martin.agren@gmail.com> writes:
>
>> On 30 August 2017 at 04:52, Michael Haggerty <mhagger@alum.mit.edu> wrote:
>>> v3 looks good to me. Thanks!
>>>
>>> Reviewed-by: Michael Haggerty <mhagger@alum.mit.edu>
>>
>> Thank _you_ for very helpful feedback on the earlier versions.
>>
>> Martin
>
> Yes, the earlier attempt was sort-of barking up a wrong tree.
>
> Once we step back and observe other users of affected_refnames and
> realize that the list is meant to to point at a refname field of an
> existing instance of another structure by borrowing, the blame
> shifts from files_transaction_prepare() to the real culprit.
> Michael's review gave us a very good "let's step back a bit" that
> made the huge improvement between v1 and v2/v3.
>
> I wonder if we should be tightening the use of affected_refnames
> even further, though.
>
> It is may be sufficient to make sure that we do not throw anything
> that we would need to free as part of destroying affected_refnames
> into the string list, purely from the "leak prevention" perspective.
>
> But stepping back a bit, the reason why the string list exists in
> the first place is to make sure we do not touch the same ref twice
> in a single transaction, the set of all possible updates in the
> single transaction exists somewhere, and each of these updates know
> what ref it wants to update.
>
> And that is recorded in transaction->updates[]->refname no?
>
> So it seems to me that logically any and all string that is
> registered in affected_refnames list must be the refname field of
> a ref_update structure in the transaction.
I'm with you up to here.
> And from that point of view, doesn't split_head_update() wants a
> similar fix? It attempts to insert "HEAD", makes sure it hasn't
> been inserted and then hangs a new update transaction as its util.
> It is not wrong per-se from purely leak-prevention point of view,
> as that "HEAD" is a literal string we woudn't even want to free,
> but from logical/"what each data means" point of view, it still
> feels wrong.
There is a "Special hack" comment related to this, and I don't feel
particularly confident that I could make any meaningful contribution in
this area. To be honest, I don't immediately see in which direction your
suggestion/idea/thought is going, which tells me I should not be making
a mess out of it. :-)
Martin
next prev parent reply other threads:[~2017-09-05 17:24 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-25 18:49 [PATCH 1/2] refs/files-backend: duplicate strings added to affected_refnames Martin Ågren
2017-08-25 18:49 ` [PATCH 2/2] refs/files-backend: fix memory leak in lock_ref_for_update Martin Ågren
2017-08-25 21:00 ` [PATCH 1/2] refs/files-backend: duplicate strings added to affected_refnames Junio C Hamano
2017-08-26 10:16 ` Martin Ågren
2017-08-28 8:06 ` Michael Haggerty
2017-08-28 10:09 ` Martin Ågren
2017-08-28 20:32 ` [PATCH v2 1/2] refs/files-backend: add longer-scoped copy of string to list Martin Ågren
2017-08-29 8:33 ` Michael Haggerty
2017-08-28 20:32 ` [PATCH v2 2/2] refs/files-backend: fix memory leak in lock_ref_for_update Martin Ågren
2017-08-29 8:39 ` Michael Haggerty
2017-08-29 10:41 ` Martin Ågren
2017-08-29 17:18 ` [PATCH v3 1/3] refs/files-backend: add longer-scoped copy of string to list Martin Ågren
2017-08-30 2:52 ` Michael Haggerty
2017-08-30 18:02 ` Martin Ågren
2017-09-05 10:02 ` Junio C Hamano
2017-09-05 17:24 ` Martin Ågren [this message]
2017-09-05 20:36 ` Jeff King
2017-09-05 21:26 ` Junio C Hamano
2017-09-06 18:12 ` Martin Ågren
2017-09-06 19:52 ` Junio C Hamano
2017-09-06 23:45 ` Jeff King
2017-09-09 6:57 ` [PATCH v4 0/4] Rerolling ma/split-symref-update-fix Martin Ågren
2017-09-09 6:57 ` [PATCH v4 1/4] refs/files-backend: add longer-scoped copy of string to list Martin Ågren
2017-09-09 6:57 ` [PATCH v4 2/4] refs/files-backend: fix memory leak in lock_ref_for_update Martin Ågren
2017-09-09 6:57 ` [PATCH v4 3/4] refs/files-backend: correct return value " Martin Ågren
2017-09-09 6:57 ` [PATCH v4 4/4] refs/files-backend: add `refname`, not "HEAD", to list Martin Ågren
2017-09-09 10:47 ` [PATCH v4 0/4] Rerolling ma/split-symref-update-fix Jeff King
2017-09-05 8:45 ` [PATCH v3 1/3] refs/files-backend: add longer-scoped copy of string to list Jeff King
2017-09-05 9:03 ` Michael Haggerty
2017-09-05 9:04 ` Jeff King
2017-08-29 17:18 ` [PATCH v3 2/3] refs/files-backend: fix memory leak in lock_ref_for_update Martin Ågren
2017-09-05 8:47 ` Jeff King
2017-09-05 17:28 ` Martin Ågren
2017-08-29 17:18 ` [PATCH v3 3/3] refs/files-backend: correct return value " Martin Ågren
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