From: David Turner <dturner@twopensource.com>
To: Michael Haggerty <mhagger@alum.mit.edu>,
Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, "Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>,
"Jeff King" <peff@peff.net>,
"Ramsay Jones" <ramsay@ramsayjones.plus.com>
Subject: Re: [PATCH 19/29] refs: don't dereference on rename
Date: Fri, 29 Apr 2016 19:21:48 -0400 [thread overview]
Message-ID: <1461972108.4123.43.camel@twopensource.com> (raw)
In-Reply-To: <57230F71.2020401@alum.mit.edu>
On Fri, 2016-04-29 at 09:38 +0200, Michael Haggerty wrote:
> On 04/27/2016 08:55 PM, Junio C Hamano wrote:
> > Michael Haggerty <mhagger@alum.mit.edu> writes:
> >
> > > @@ -2380,8 +2381,8 @@ int rename_ref(const char *oldrefname,
> > > const char *newrefname, const char *logms
> > > goto rollback;
> > > }
> > >
> > > - if (!read_ref_full(newrefname, RESOLVE_REF_READING,
> > > sha1, NULL) &&
> > > - delete_ref(newrefname, sha1, REF_NODEREF)) {
> > > + if (!read_ref_full(newrefname, resolve_flags, sha1,
> > > NULL) &&
> > > + delete_ref(newrefname, NULL, REF_NODEREF)) {
> >
> > Could you explain s/sha1/NULL/ here in the proposed log message?
>
> Good question.
>
> Passing sha1 to delete_ref() doesn't add any safety, because the same
> sha1 was just read a moment before, and it is not used for anything
> else. So the check only protects us from a concurrent update to
> newrefname between the call to read_ref_full() and the call to
> delete_ref(). But such a race is indistinguishable from the case that
> a
> modification to newrefname happens just before the call to
> read_ref_full(), which would have the same outcome as the new code.
> So
> the "sha1" check only adds ways for the rename() to fail in
> situations
> where nothing harmful would have happened anyway.
>
> That being said, this is a very unlikely race, and I don't think it
> matters much either way. In any case, the change s/sha1/NULL/ here
> seems
> orthogonal to the rest of the patch.
>
> David, you wrote the original version of this patch. Am I overlooking
> something?
I think I might have been handling some weird case related to symbolic
refs, but I don't recall the details. Your argument seems right to me.
next prev parent reply other threads:[~2016-04-29 23:21 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-27 16:57 [PATCH 00/29] Yet more preparation for reference backends Michael Haggerty
2016-04-27 16:57 ` [PATCH 01/29] safe_create_leading_directories(): improve docstring Michael Haggerty
2016-04-27 16:57 ` [PATCH 02/29] remove_dir_recursively(): add docstring Michael Haggerty
2016-04-27 16:57 ` [PATCH 03/29] refname_is_safe(): use skip_prefix() Michael Haggerty
2016-04-27 16:57 ` [PATCH 04/29] refname_is_safe(): don't allow the empty string Michael Haggerty
2016-04-27 16:57 ` [PATCH 05/29] refname_is_safe(): insist that the refname already be normalized Michael Haggerty
2016-04-27 17:59 ` Junio C Hamano
2016-04-27 20:10 ` David Turner
2016-04-27 20:15 ` Jeff King
2016-04-27 20:34 ` David Turner
2016-04-27 20:37 ` Jeff King
2016-04-27 22:19 ` Jeff King
2016-04-28 17:44 ` David Turner
2016-04-27 16:57 ` [PATCH 06/29] commit_ref_update(): write error message to *err, not stderr Michael Haggerty
2016-04-27 16:57 ` [PATCH 07/29] rename_ref(): remove unneeded local variable Michael Haggerty
2016-04-27 16:57 ` [PATCH 08/29] ref_transaction_commit(): remove local variable n Michael Haggerty
2016-04-27 18:16 ` Junio C Hamano
2016-04-27 20:45 ` Junio C Hamano
2016-04-27 16:57 ` [PATCH 09/29] read_raw_ref(): rename flags argument to type Michael Haggerty
2016-04-27 16:57 ` [PATCH 10/29] read_raw_ref(): clear *type at start of function Michael Haggerty
2016-04-27 16:57 ` [PATCH 11/29] read_raw_ref(): rename symref argument to referent Michael Haggerty
2016-04-27 16:57 ` [PATCH 12/29] read_raw_ref(): improve docstring Michael Haggerty
2016-04-27 18:31 ` Junio C Hamano
2016-04-27 16:57 ` [PATCH 13/29] lock_ref_sha1_basic(): remove unneeded local variable Michael Haggerty
2016-04-27 16:57 ` [PATCH 14/29] refs: make error messages more consistent Michael Haggerty
2016-04-27 16:57 ` [PATCH 15/29] ref_transaction_create(): disallow recursive pruning Michael Haggerty
2016-04-27 18:47 ` Junio C Hamano
2016-04-27 20:23 ` David Turner
2016-04-27 20:45 ` Junio C Hamano
2016-04-27 21:15 ` Junio C Hamano
2016-04-28 17:48 ` David Turner
2016-04-28 20:15 ` Junio C Hamano
2016-04-29 6:56 ` Michael Haggerty
2016-04-29 8:19 ` Junio C Hamano
2016-04-29 8:41 ` Junio C Hamano
2016-04-29 14:29 ` Michael Haggerty
2016-04-27 16:57 ` [PATCH 16/29] ref_transaction_commit(): correctly report close_ref() failure Michael Haggerty
2016-04-27 16:57 ` [PATCH 17/29] delete_branches(): use resolve_refdup() Michael Haggerty
2016-04-27 16:57 ` [PATCH 18/29] refs: allow log-only updates Michael Haggerty
2016-04-27 16:57 ` [PATCH 19/29] refs: don't dereference on rename Michael Haggerty
2016-04-27 18:55 ` Junio C Hamano
2016-04-29 7:38 ` Michael Haggerty
2016-04-29 8:53 ` Junio C Hamano
2016-04-29 10:57 ` Michael Haggerty
2016-04-29 12:12 ` Jeff King
2016-04-29 13:55 ` Michael Haggerty
2016-04-29 14:08 ` Jeff King
2016-04-29 15:29 ` Junio C Hamano
2016-04-29 23:21 ` David Turner [this message]
2016-04-30 3:48 ` Michael Haggerty
2016-05-02 17:55 ` Junio C Hamano
2016-04-27 16:57 ` [PATCH 20/29] verify_refname_available(): adjust constness in declaration Michael Haggerty
2016-04-27 16:57 ` [PATCH 21/29] add_update(): initialize the whole ref_update Michael Haggerty
2016-04-27 16:57 ` [PATCH 22/29] lock_ref_for_update(): new function Michael Haggerty
2016-04-27 16:57 ` [PATCH 23/29] unlock_ref(): move definition higher in the file Michael Haggerty
2016-04-27 16:57 ` [PATCH 24/29] ref_transaction_update(): check refname_is_safe() at a minimum Michael Haggerty
2016-04-27 20:14 ` Junio C Hamano
2016-04-29 7:42 ` Michael Haggerty
2016-04-29 8:53 ` Junio C Hamano
2016-04-27 16:57 ` [PATCH 25/29] refs: resolve symbolic refs first Michael Haggerty
2016-04-28 23:40 ` David Turner
2016-04-29 9:51 ` Michael Haggerty
2016-04-29 23:14 ` David Turner
2016-05-02 18:06 ` Junio C Hamano
2016-04-27 16:57 ` [PATCH 26/29] lock_ref_for_update(): don't re-read non-symbolic references Michael Haggerty
2016-04-27 16:57 ` [PATCH 27/29] lock_ref_for_update(): don't resolve symrefs Michael Haggerty
2016-04-27 16:57 ` [PATCH 28/29] commit_ref_update(): remove the flags parameter Michael Haggerty
2016-04-27 16:57 ` [PATCH 29/29] lock_ref_sha1_basic(): only handle REF_NODEREF mode Michael Haggerty
2016-04-29 15:43 ` Junio C Hamano
2016-04-29 1:14 ` [PATCH 00/29] Yet more preparation for reference backends David Turner
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