linux-kernel - [PATCH] powerpc: fix __get_user_pages

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Message-ID: <20131008075111.GB4252@osiris>
Date:	Tue, 8 Oct 2013 09:51:11 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] powerpc: fix __get_user_pages_fast() irq handling

>From 1454d5ca6209926a52c2fdea9ba41a41a33e4046 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens@...ibm.com>
Date: Tue, 8 Oct 2013 09:46:00 +0200
Subject: [PATCH] powerpc: fix __get_user_pages_fast() irq handling

__get_user_pages_fast() may be called with interrupts disabled (see e.g.
get_futex_key() in kernel/futex.c) and therefore should use local_irq_save()
and local_irq_restore() instead of local_irq_disable()/enable().

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---

Please note that this patch is completely untested; not even compile
tested. I just realized that there seems to be a bug when looking at
the powerpc code ;)

 arch/powerpc/mm/gup.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/gup.c b/arch/powerpc/mm/gup.c
index 6936547..c5f734e 100644
--- a/arch/powerpc/mm/gup.c
+++ b/arch/powerpc/mm/gup.c
@@ -123,6 +123,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	struct mm_struct *mm = current->mm;
 	unsigned long addr, len, end;
 	unsigned long next;
+	unsigned long flags;
 	pgd_t *pgdp;
 	int nr = 0;
 
@@ -156,7 +157,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	 * So long as we atomically load page table pointers versus teardown,
 	 * we can follow the address down to the the page and take a ref on it.
 	 */
-	local_irq_disable();
+	local_irq_save(flags);
 
 	pgdp = pgd_offset(mm, addr);
 	do {
@@ -179,7 +180,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 			break;
 	} while (pgdp++, addr = next, addr != end);
 
-	local_irq_enable();
+	local_irq_restore(flags);
 
 	return nr;
 }
-- 
1.8.3.4

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