> /* > * 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. > 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.
