linux-kernel - [PATCH v6 02/11] mm/gup: Use functions to track lockless pgtbl walks on gup_pgd

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Date:   Thu,  6 Feb 2020 00:08:51 -0300
From:   Leonardo Bras <leonardo@...ux.ibm.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        Steven Price <steven.price@....com>,
        Robin Murphy <robin.murphy@....com>,
        Leonardo Bras <leonardo@...ux.ibm.com>,
        Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        Reza Arbab <arbab@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Allison Randal <allison@...utok.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michal Suchanek <msuchanek@...e.de>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org
Subject: [PATCH v6 02/11] mm/gup: Use functions to track lockless pgtbl walks on gup_pgd_range

As described, gup_pgd_range is a lockless pagetable walk. So, in order to
track against THP split/collapse, it disables/enables irq around it.

To make use of the new tracking functions, it replaces irq disable/enable
by {begin,end}_lockless_pgtbl_walk().

As local_irq_{save,restore} is present inside
{begin,end}_lockless_pgtbl_walk, there should be no change in the
workings.

Signed-off-by: Leonardo Bras <leonardo@...ux.ibm.com>
---
 mm/gup.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 1b521e0ac1de..04e6f46993b6 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2369,7 +2369,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 			  struct page **pages)
 {
 	unsigned long len, end;
-	unsigned long flags;
+	unsigned long irq_mask;
 	int nr = 0;
 
 	start = untagged_addr(start) & PAGE_MASK;
@@ -2395,9 +2395,9 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 
 	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
 	    gup_fast_permitted(start, end)) {
-		local_irq_save(flags);
+		irq_mask = begin_lockless_pgtbl_walk();
 		gup_pgd_range(start, end, write ? FOLL_WRITE : 0, pages, &nr);
-		local_irq_restore(flags);
+		end_lockless_pgtbl_walk(irq_mask);
 	}
 
 	return nr;
@@ -2450,9 +2450,9 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
 
 	if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
 	    gup_fast_permitted(start, end)) {
-		local_irq_disable();
+		begin_lockless_pgtbl_walk();
 		gup_pgd_range(addr, end, gup_flags, pages, &nr);
-		local_irq_enable();
+		end_lockless_pgtbl_walk(IRQS_ENABLED);
 		ret = nr;
 	}
 
-- 
2.24.1