[merged mm-stable] mm-gup-update-comment-explaining-why-gup_fast-disables-irqs.patch removed from -mm tree

[merged mm-stable] mm-gup-update-comment-explaining-why-gup_fast-disables-irqs.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/gup: update comment explaining why gup_fast() disables IRQs
has been removed from the -mm tree.  Its filename was
     mm-gup-update-comment-explaining-why-gup_fast-disables-irqs.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Jann Horn <jannh@google.com>
Subject: mm/gup: update comment explaining why gup_fast() disables IRQs
Date: Wed, 28 May 2025 23:06:17 +0200

The current comment in gup_fast() talks about "IPIs that come from THPs
splitting", which is outdated and refers to the old THP splitting
implementation that was removed in commit ad0bed24e98b ("thp: drop all
split_huge_page()-related code"), which landed in v4.5.  Before then, THP
splitting involved a pmdp_splitting_flush(), which sent an IPI to
serialize against gup_fast().

Nowadays, we use tlb_remove_table_sync_one() to send IPIs that serialize
against gup_fast(); this is used, for example, in THP *collapsing* to stop
gup_fast() walks of a page table before depositing it.

Link: https://lkml.kernel.org/r/20250528-gup-irq-comment-fix-v1-1-b9d83c345333@google.com
Signed-off-by: Jann Horn <jannh@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kirill A. Shuemov <kirill.shutemov@linux.intel.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/gup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/gup.c~mm-gup-update-comment-explaining-why-gup_fast-disables-irqs
+++ a/mm/gup.c
@@ -3299,7 +3299,7 @@ static unsigned long gup_fast(unsigned l
 	 * include/asm-generic/tlb.h for more details.
 	 *
 	 * We do not adopt an rcu_read_lock() here as we also want to block IPIs
-	 * that come from THPs splitting.
+	 * that come from callers of tlb_remove_table_sync_one().
 	 */
 	local_irq_save(flags);
 	gup_fast_pgd_range(start, end, gup_flags, pages, &nr_pinned);
_

Patches currently in -mm which might be from jannh@google.com are

mm-hugetlb-unshare-page-tables-during-vma-split-not-before.patch
mm-hugetlb-unshare-page-tables-during-vma-split-not-before-v2.patch
mm-hugetlb-fix-huge_pmd_unshare-vs-gup-fast-race.patch