Re: [PATCH 4.9 1/2] Revert "gup: document and work around "COW can break either way" issue"

On Mon, Jan 24, 2022 at 02:38:28PM +0100, Ben Hutchings wrote:

This reverts commit 9bbd42e79720122334226afad9ddcac1c3e6d373, which was commit 17839856fd588f4ab6b789f482ed3ffd7c403e1f upstream. The backport was incorrect and incomplete:

• It forced the write flag on in the generic __get_user_pages_fast(), whereas only get_user_pages_fast() was supposed to do that.
• It only fixed the generic RCU-based implementation used by arm, arm64, and powerpc. Before Linux 4.13, several other architectures had their own implementations: mips, s390, sparc, sh, and x86.

This will be followed by a (hopefully) correct backport.

Signed-off-by: Ben Hutchings ben@decadent.org.uk Cc: Suren Baghdasaryan surenb@google.com Cc: stable@vger.kernel.org

---

mm/gup.c | 48 ++++++++---------------------------------------- mm/huge_memory.c | 7 ++++--- 2 files changed, 12 insertions(+), 43 deletions(-)

Both now queued up, thanks!

greg k-h