linux-kernel - [PATCH 5/6] powerpc/mmu: drop mmap_sem now that locked

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Date:   Tue,  2 Apr 2019 16:41:57 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     akpm@...ux-foundation.org
Cc:     daniel.m.jordan@...cle.com, Alexey Kardashevskiy <aik@...abs.ru>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Lameter <cl@...ux.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH 5/6] powerpc/mmu: drop mmap_sem now that locked_vm is atomic

With locked_vm now an atomic, there is no need to take mmap_sem as
writer.  Delete and refactor accordingly.

Signed-off-by: Daniel Jordan <daniel.m.jordan@...cle.com>
Cc: Alexey Kardashevskiy <aik@...abs.ru>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Davidlohr Bueso <dave@...olabs.net>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: <linux-mm@...ck.org>
Cc: <linuxppc-dev@...ts.ozlabs.org>
Cc: <linux-kernel@...r.kernel.org>
---
 arch/powerpc/mm/mmu_context_iommu.c | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
index 8038ac24a312..a4ef22b67c07 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c
@@ -54,34 +54,29 @@ struct mm_iommu_table_group_mem_t {
 static long mm_iommu_adjust_locked_vm(struct mm_struct *mm,
 		unsigned long npages, bool incr)
 {
-	long ret = 0, locked, lock_limit;
+	long ret = 0;
+	unsigned long lock_limit;
 	s64 locked_vm;
 
 	if (!npages)
 		return 0;
 
-	down_write(&mm->mmap_sem);
-	locked_vm = atomic64_read(&mm->locked_vm);
 	if (incr) {
-		locked = locked_vm + npages;
 		lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
-		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
+		locked_vm = atomic64_add_return(npages, &mm->locked_vm);
+		if (locked_vm > lock_limit && !capable(CAP_IPC_LOCK)) {
 			ret = -ENOMEM;
-		else
-			atomic64_add(npages, &mm->locked_vm);
+			atomic64_sub(npages, &mm->locked_vm);
+		}
 	} else {
-		if (WARN_ON_ONCE(npages > locked_vm))
-			npages = locked_vm;
-		atomic64_sub(npages, &mm->locked_vm);
+		locked_vm = atomic64_sub_return(npages, &mm->locked_vm);
+		WARN_ON_ONCE(locked_vm < 0);
 	}
 
-	pr_debug("[%d] RLIMIT_MEMLOCK HASH64 %c%ld %ld/%ld\n",
-			current ? current->pid : 0,
-			incr ? '+' : '-',
-			npages << PAGE_SHIFT,
-			atomic64_read(&mm->locked_vm) << PAGE_SHIFT,
+	pr_debug("[%d] RLIMIT_MEMLOCK HASH64 %c%lu %lld/%lu\n",
+			current ? current->pid : 0, incr ? '+' : '-',
+			npages << PAGE_SHIFT, locked_vm << PAGE_SHIFT,
 			rlimit(RLIMIT_MEMLOCK));
-	up_write(&mm->mmap_sem);
 
 	return ret;
 }
-- 
2.21.0