Re: [PATCH v2 7/8] submodule-config: pass repo upon blob config read
From: Jonathan Tan <hidden>
Date: 2021-08-16 20:02:29
/* * 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.
I think you can make the patch yourself - the comment change you describe seems unrelated to this patch set.
quoted hunk ↗ jump to hunk
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.
Thanks for checking this. I'll mention this in the commit message.