Subject: [PATCH v2 05/11] powerpc/perf: Applies counting method to monitor lockless pgtbl walks

From: Leonardo Bras <[email-masked]>
Date: Fri, 20 Sep 2019 16:50:41 -0300

Applies the counting-based method for monitoring lockless pgtable walks on
read_user_stack_slow.

Signed-off-by: Leonardo Bras <[email-masked]>
---
 arch/powerpc/perf/callchain.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
index c84bbd4298a0..9d76194a2a8f 100644
--- a/arch/powerpc/perf/callchain.c
+++ b/arch/powerpc/perf/callchain.c
@@ -113,16 +113,18 @@ static int read_user_stack_slow(void __user *ptr, void *buf, int nb)
 	int ret = -EFAULT;
 	pgd_t *pgdir;
 	pte_t *ptep, pte;
+	struct mm_struct *mm = current->mm;
 	unsigned shift;
 	unsigned long addr = (unsigned long) ptr;
 	unsigned long offset;
 	unsigned long pfn, flags;
 	void *kaddr;
 
-	pgdir = current->mm->pgd;
+	pgdir = mm->pgd;
 	if (!pgdir)
 		return -EFAULT;
 
+	start_lockless_pgtbl_walk(mm);
 	local_irq_save(flags);
 	ptep = find_current_mm_pte(pgdir, addr, NULL, &shift);
 	if (!ptep)
@@ -146,6 +148,7 @@ static int read_user_stack_slow(void __user *ptr, void *buf, int nb)
 	ret = 0;
 err_out:
 	local_irq_restore(flags);
+	end_lockless_pgtbl_walk(mm);
 	return ret;
 }
 
-- 
2.20.1