Re: [PATCH v2 7/8] submodule-config: pass repo upon blob config read
- From
Matheus Tavares Bernardino <matheus.bernardino@usp.br>
- Date
- Aug 16, 2021, 14:32 UTC
- Message-ID
- <CAHd-oW7nv-Y_QmhA2gcX5GoWxus88inmbcXQ5kPiSRLBdhtoUw@mail.gmail.com>
- In-Reply-To
- <94db10a4e5943d689113693c64633ddffa5508cc.1628888668.git.jonathantanmy@google.com>
On Fri, Aug 13, 2021 at 6:05 PM Jonathan Tan <jonathantanmy@google.com> wrote:
Show 5 quoted lines
> > When reading the config of a submodule, if reading from a blob, read > using an explicitly specified repository instead of by adding the > submodule's ODB as an alternate and then reading an object from > the_repository.
Great!
At first, I thought this would also allow us to remove another NEEDSWORK comment in grep_submodule(), together with a lock protection:
/* * NEEDSWORK: repo_read_gitmodules() might call * add_to_alternates_memory() via config_from_gitmodules(). This * operation causes a race condition with concurrent object readings * performed by the worker threads. That's why we need obj_read_lock() * here. It should be removed once it's no longer necessary to add the * subrepo's odbs to the in-memory alternates list. */ obj_read_lock(); repo_read_gitmodules(subrepo, 0);
Back when I wrote this comment, my conclusion was that the alternates mechanics were the only thread-unsafe object-reading operations in repo_read_gitmodules()'s call chains. So once the add-to-alternates mechanics were gone, we could also remove the lock.
But with further inspection now, I see that this is not really the case. For example, we have a few global variables in packfile.c collecting some statistics (pack_mmap_calls, pack_open_windows, etc.) which are updated on obj readings from both the_repository *and* submodules. So I no longer think its safe to remove the obj_read_lock() protection here, as the NEEDSWORK comment suggests, even if we are not using the alternates list anymore.
Do you want to remove this comment in your patchset? I can also send a follow-up patch explaining this situation and removing the comment (but not the locking), if you prefer.
> Signed-off-by: Jonathan Tan <jonathantanmy@google.com> > ---
[...]
Show 13 quoted lines
> diff --git a/submodule-config.c b/submodule-config.c
> index 2026120fb3..f95344028b 100644
> --- a/submodule-config.c
> +++ b/submodule-config.c
> @@ -649,9 +649,10 @@ static void config_from_gitmodules(config_fn_t fn, struct repository *repo, void
> config_source.file = file;
> } else if (repo_get_oid(repo, GITMODULES_INDEX, &oid) >= 0 ||
> repo_get_oid(repo, GITMODULES_HEAD, &oid) >= 0) {
> + config_source.repo = repo;
> config_source.blob = oidstr = xstrdup(oid_to_hex(&oid));
> if (repo != the_repository)
> - add_to_alternates_memory(repo->objects->odb->path);
> + add_submodule_odb_by_path(repo->objects->odb->path);Ok. Like in grep_submodule(), this should no longer add the submodule ODB to the alternates list, so this call is now mostly used as a fallback and also for testing.
To see if we are indeed testing this add-to-alternates case, I reverted the change that made the code read from the submodule instead of the_repository:
diff --git a/config.c b/config.c index a85c12e6cc..cd37a9dcd9 100644 --- a/config.c +++ b/config.c @@ -1805,7 +1805,7 @@ int git_config_from_blob_oid(config_fn_t fn, unsigned long size; int ret; - buf = repo_read_object_file(repo, oid, &type, &size); + buf = read_object_file(oid, &type, &size); Then, I ran t7814-grep-recurse-submodules.sh , where you've added the GIT_TEST_FATAL_REGISTER_SUBMODULE_ODB=1 envvar. This correctly produced the following error: BUG: submodule.c:205: register_all_submodule_odb_as_alternates() called [...] not ok 23 - grep --recurse-submodules with submodules without .gitmodules in the working tree Nice! So the change made by this patch is covered by test 23. I think it would be nice to mention that in this patch's message.