linux-kernel - [PATCH v3 05/11] powerpc/perf: Applies counting method to monitor lockless pgtbl walks

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Date:   Tue, 24 Sep 2019 18:24:22 -0300
From:   Leonardo Bras <leonardo@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org
Cc:     Leonardo Bras <leonardo@...ux.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Arnd Bergmann <arnd@...db.de>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ganesh Goudar <ganeshgr@...ux.ibm.com>,
        Allison Randal <allison@...utok.net>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>,
        Keith Busch <keith.busch@...el.com>
Subject: [PATCH v3 05/11] powerpc/perf: Applies counting method to monitor lockless pgtbl walks

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

Signed-off-by: Leonardo Bras <leonardo@...ux.ibm.com>
---
 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