On Mon, 3 Jul 2023 at 12:59, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
>
> The patch 8d7071af8907 ("mm: always expand the stack with the mmap write
> lock held") breaks PA-RISC.
>
> The breakage happens if we attempt to pass more arguments to execve than
> what fits into the initial stack page - we get -E2BIG in such a case.
>
> The reason for the breakage is that the commit 8d7071af8907 adds the test
> "if (!(vma->vm_flags & VM_GROWSDOWN)) return -EFAULT;" to the function
> expand_downwards.
Heh. See
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f66066bc5136f25e36a2daff4896c768f18c211e
which fixes this differently (and, I think, much better).
Just removing the VM_GROWSDOWN test will actually break some of the other users.
Notably the new and improved expand_stack() function that now handles
all the complicated *cough*ia64*cough* cases automatically, which
allowed unifying the page fault handling code around this area.
Linus
