diff mbox series

[4.9,55/83] mm, gup: remove broken VM_BUG_ON_PAGE compound check for hugepages

Message ID 20190609164132.620872548@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg Kroah-Hartman June 9, 2019, 4:42 p.m. UTC 
From: Will Deacon <will.deacon@arm.com>


commit a3e328556d41bb61c55f9dfcc62d6a826ea97b85 upstream.

When operating on hugepages with DEBUG_VM enabled, the GUP code checks
the compound head for each tail page prior to calling
page_cache_add_speculative.  This is broken, because on the fast-GUP
path (where we don't hold any page table locks) we can be racing with a
concurrent invocation of split_huge_page_to_list.

split_huge_page_to_list deals with this race by using page_ref_freeze to
freeze the page and force concurrent GUPs to fail whilst the component
pages are modified.  This modification includes clearing the
compound_head field for the tail pages, so checking this prior to a
successful call to page_cache_add_speculative can lead to false
positives: In fact, page_cache_add_speculative *already* has this check
once the page refcount has been successfully updated, so we can simply
remove the broken calls to VM_BUG_ON_PAGE.

Link: http://lkml.kernel.org/r/20170522133604.11392-2-punit.agrawal@arm.com
Signed-off-by: Will Deacon <will.deacon@arm.com>

Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>

Acked-by: Steve Capper <steve.capper@arm.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/gup.c |    3 ---
 1 file changed, 3 deletions(-)
diff mbox series

Patch

--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1316,7 +1316,6 @@  static int gup_huge_pmd(pmd_t orig, pmd_
 	head = pmd_page(orig);
 	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
 	do {
-		VM_BUG_ON_PAGE(compound_head(page) != head, page);
 		pages[*nr] = page;
 		(*nr)++;
 		page++;
@@ -1351,7 +1350,6 @@  static int gup_huge_pud(pud_t orig, pud_
 	head = pud_page(orig);
 	page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 	do {
-		VM_BUG_ON_PAGE(compound_head(page) != head, page);
 		pages[*nr] = page;
 		(*nr)++;
 		page++;
@@ -1387,7 +1385,6 @@  static int gup_huge_pgd(pgd_t orig, pgd_
 	head = pgd_page(orig);
 	page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
 	do {
-		VM_BUG_ON_PAGE(compound_head(page) != head, page);
 		pages[*nr] = page;
 		(*nr)++;
 		page++;