On Thu, Oct 1, 2020 at 6:25 PM Jann Horn <jannh@xxxxxxxxxx> wrote: > Until now, the mmap lock of the nascent mm was ordered inside the mmap lock > of the old mm (in dup_mmap() and in UML's activate_mm()). > A following patch will change the exec path to very broadly lock the > nascent mm, but fine-grained locking should still work at the same time for > the new mm. > To do this in a way that lockdep is happy about, let's turn around the lock > ordering in both places that currently nest the locks. > Since SINGLE_DEPTH_NESTING is normally used for the inner nesting layer, > make up our own lock subclass MMAP_LOCK_SUBCLASS_NASCENT and use that > instead. > > The added locking calls in exec_mmap() are temporary; the following patch > will move the locking out of exec_mmap(). Thanks for doing this. This is probably a silly question, but I am not sure exactly where we lock the old MM while bprm is creating the new MM ? I am guessing this would be only in setup_arg_pages(), copying the args and environment from the old the the new MM ? If that is correct, then wouldn't it be sufficient to use mmap_write_lock_nested in setup_arg_pages() ? Or, is the issue that we'd prefer to have a killable version of it there ? Also FYI I was going to play with these patches a bit to help answer these questions on my own, but wasn't able to easily apply them as they came lightly mangled (whitespace issues) when I saved them.
