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Date: Wed, 27 Oct 2010 16:54:21 +0200
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: Christoph Hellwig <hch@...radead.org>
Cc: linux-kernel@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-mm <linux-mm@...ck.org>,
linux-arch <linux-arch@...r.kernel.org>, riel <riel@...hat.com>
Subject: [RFT][PATCH] mm: Fix race in kunmap_atomic()
On Wed, 2010-10-27 at 08:51 -0400, Christoph Hellwig wrote:
> I haven't tracked it down to the kmap_atomic rework but it seems
> rather likely:
>
> [ 2111.896469] ------------[ cut here ]------------
> [ 2111.898408] kernel BUG at /home/hch/work/linux-2.6/arch/x86/mm/highmem_32.c:46!
> [ 2111.900385] invalid opcode: 0000 [#1] SMP
> [ 2111.900385] last sysfs file: /sys/devices/virtio-pci/virtio1/block/vdb/removable
> [ 2111.900385] Modules linked in:
> [ 2111.900385]
> [ 2111.900385] Pid: 10286, comm: aio-stress Not tainted 2.6.36+ #32 /Bochs
> [ 2111.900385] EIP: 0060:[<c0158e5c>] EFLAGS: 00010006 CPU: 0
> [ 2111.900385] EIP is at kmap_atomic_prot+0xec/0xf0
> [ 2111.900385] EAX: f75df040 EBX: 00000001 ECX: 3c6d7163 EDX: 00000163
> [ 2111.900385] ESI: fffffffc EDI: 00000001 EBP: f6801e5c ESP: f6801e4c
> [ 2111.900385] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
> [ 2111.900385] Process aio-stress (pid: 10286, ti=f6800000 task=f13c8280task.ti=f1356000)
> [ 2111.900385] Stack:
> [ 2111.900385] fffff000 f2840ef0 f20ac690 00010000 f6801e64 c0158e6e f6801e9c c024ee0d
> [ 2111.900385] <0> ffffffff 00000000 f6801eac 00000046 f13c870c 00000002 00000000 00000096
> [ 2111.900385] <0> f20ac6d8 d4c23950 00010000 00000000 f6801ed0 c0244be7 d4c23a24 00000096
> [ 2111.900385] Call Trace:
> [ 2111.900385] [<c0158e6e>] ? __kmap_atomic+0xe/0x10
> [ 2111.900385] [<c024ee0d>] ? aio_complete+0xdd/0x1a0
> [ 2111.900385] [<c0244be7>] ? dio_complete+0x107/0x110
> [ 2111.900385] [<c0244c35>] ? dio_bio_end_aio+0x45/0xa0
> [ 2111.900385] [<c0244c5b>] ? dio_bio_end_aio+0x6b/0xa0
> [ 2111.900385] [<c02407a5>] ? bio_endio+0x15/0x30
> [ 2111.900385] [<c071b4c2>] ? req_bio_endio+0xa2/0x100
> [ 2111.900385] [<c071bdfe>] ? blk_update_request+0x17e/0x420
> [ 2111.900385] [<c071bd69>] ? blk_update_request+0xe9/0x420
> [ 2111.900385] [<c071bdfe>] ? blk_update_request+0x17e/0x420
> [ 2111.900385] [<c021320e>] ? kfree+0xfe/0x170
> [ 2111.900385] [<c071c0b6>] ? blk_update_bidi_request+0x16/0x80
> [ 2111.900385] [<c071da55>] ? __blk_end_request_all+0x25/0x50
> [ 2111.900385] [<c07bf212>] ? blk_done+0x42/0xd0
> [ 2111.900385] [<c0787ec4>] ? vring_interrupt+0x24/0x40
> [ 2111.900385] [<c01ba684>] ? handle_IRQ_event+0x44/0x160
> [ 2111.900385] [<c01bc5ac>] ? handle_edge_irq+0x9c/0x140
> [ 2111.900385] [<c01bc5b6>] ? handle_edge_irq+0xa6/0x140
> [ 2111.900385] [<c01bc510>] ? handle_edge_irq+0x0/0x140
> [ 2111.900385] <IRQ>
> [ 2111.900385] [<c0135dd4>] ? do_IRQ+0x44/0xc0
> [ 2111.900385] [<c017b556>] ? run_timer_softirq+0xd6/0x350
> [ 2111.900385] [<c01739d0>] ? __do_softirq+0x0/0x1f0
> [ 2111.900385] [<c013502e>] ? common_interrupt+0x2e/0x34
> [ 2111.900385] [<c01367c4>] ? do_softirq+0x94/0xe0
> [ 2111.900385] [<c01739d0>] ? __do_softirq+0x0/0x1f0
> [ 2111.900385] [<c0173a20>] ? __do_softirq+0x50/0x1f0
> [ 2111.900385] [<c0173a22>] ? __do_softirq+0x52/0x1f0
> [ 2111.900385] [<c01739d0>] ? __do_softirq+0x0/0x1f0
> [ 2111.900385] <IRQ>
> [ 2111.900385] [<c017384d>] ? irq_exit+0x6d/0x80
> [ 2111.900385] [<c014b3b6>] ? smp_apic_timer_interrupt+0x56/0x90
> [ 2111.900385] [<c0736f04>] ? trace_hardirqs_off_thunk+0xc/0x18
> [ 2111.900385] [<c0a07167>] ? apic_timer_interrupt+0x2f/0x34
> [ 2111.900385] [<c0153691>] ? native_set_pte_at+0x1/0x10
> [ 2111.900385] [<c0158cc0>] ? __kunmap_atomic+0x70/0xa0
> [ 2111.900385] [<c024e32a>] ? aio_read_evt+0xca/0xf0
> [ 2111.900385] [<c024f16f>] ? read_events+0xcf/0x340
> [ 2111.900385] [<c019ff0b>] ? trace_hardirqs_on+0xb/0x10
> [ 2111.900385] [<c0153f65>] ? pvclock_clocksource_read+0xf5/0x190
> [ 2111.900385] [<c0169660>] ? default_wake_function+0x0/0x10
> [ 2111.900385] [<c024f423>] ? sys_io_getevents+0x43/0x90
> [ 2111.900385] [<c0a06cdd>] ? syscall_call+0x7/0xb
Ooh, nice.. I think the below patch cures this but haven't actually
managed to install xfstest inside a qemu thing yet.
---
Subject: mm: Fix race in kunmap_atomic()
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date: Wed Oct 27 16:42:10 CEST 2010
Christoph reported a nice splat which illustrated a race in the new
stack based kmap_atomic implementation.
The problem is that we pop our stack slot before we're completely done
resetting its state -- in particular clearing the PTE (sometimes that's
CONFIG_DEBUG_HIGHMEM). If an interrupt happens before we actually clear
the PTE used for the last slot, that interrupt can reuse the slot in a
dirty state, which triggers a BUG in kmap_atomic().
Fix this by introducing kmap_atomic_idx() which reports the current slot
index without actually releasing it and use that to find the PTE and
delay the _pop() until after we're completely done.
Reported-by: Christoph Hellwig <hch@...radead.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
arch/arm/mm/highmem.c | 3 ++-
arch/frv/mm/highmem.c | 3 ++-
arch/mips/mm/highmem.c | 3 ++-
arch/mn10300/include/asm/highmem.h | 4 +++-
arch/powerpc/mm/highmem.c | 4 +++-
arch/sparc/mm/highmem.c | 4 +++-
arch/tile/mm/highmem.c | 3 ++-
arch/x86/mm/highmem_32.c | 3 ++-
arch/x86/mm/iomap_32.c | 3 ++-
include/linux/highmem.h | 5 +++++
10 files changed, 26 insertions(+), 9 deletions(-)
Index: linux-2.6/arch/arm/mm/highmem.c
===================================================================
--- linux-2.6.orig/arch/arm/mm/highmem.c
+++ linux-2.6/arch/arm/mm/highmem.c
@@ -89,7 +89,7 @@ void __kunmap_atomic(void *kvaddr)
int idx, type;
if (kvaddr >= (void *)FIXADDR_START) {
- type = kmap_atomic_idx_pop();
+ type = kmap_atomic_idx();
idx = type + KM_TYPE_NR * smp_processor_id();
if (cache_is_vivt())
@@ -101,6 +101,7 @@ void __kunmap_atomic(void *kvaddr)
#else
(void) idx; /* to kill a warning */
#endif
+ kmap_atomic_idx_pop();
} else if (vaddr >= PKMAP_ADDR(0) && vaddr < PKMAP_ADDR(LAST_PKMAP)) {
/* this address was obtained through kmap_high_get() */
kunmap_high(pte_page(pkmap_page_table[PKMAP_NR(vaddr)]));
Index: linux-2.6/arch/frv/mm/highmem.c
===================================================================
--- linux-2.6.orig/arch/frv/mm/highmem.c
+++ linux-2.6/arch/frv/mm/highmem.c
@@ -68,7 +68,7 @@ EXPORT_SYMBOL(__kmap_atomic);
void __kunmap_atomic(void *kvaddr)
{
- int type = kmap_atomic_idx_pop();
+ int type = kmap_atomic_idx();
switch (type) {
case 0: __kunmap_atomic_primary(4, 6); break;
case 1: __kunmap_atomic_primary(5, 7); break;
@@ -83,6 +83,7 @@ void __kunmap_atomic(void *kvaddr)
default:
BUG();
}
+ kmap_atomic_idx_pop();
pagefault_enable();
}
EXPORT_SYMBOL(__kunmap_atomic);
Index: linux-2.6/arch/mips/mm/highmem.c
===================================================================
--- linux-2.6.orig/arch/mips/mm/highmem.c
+++ linux-2.6/arch/mips/mm/highmem.c
@@ -74,7 +74,7 @@ void __kunmap_atomic(void *kvaddr)
return;
}
- type = kmap_atomic_idx_pop();
+ type = kmap_atomic_idx();
#ifdef CONFIG_DEBUG_HIGHMEM
{
int idx = type + KM_TYPE_NR * smp_processor_id();
@@ -89,6 +89,7 @@ void __kunmap_atomic(void *kvaddr)
local_flush_tlb_one(vaddr);
}
#endif
+ kmap_atomic_idx_pop();
pagefault_enable();
}
EXPORT_SYMBOL(__kunmap_atomic);
Index: linux-2.6/arch/mn10300/include/asm/highmem.h
===================================================================
--- linux-2.6.orig/arch/mn10300/include/asm/highmem.h
+++ linux-2.6/arch/mn10300/include/asm/highmem.h
@@ -101,7 +101,7 @@ static inline void __kunmap_atomic(unsig
return;
}
- type = kmap_atomic_idx_pop();
+ type = kmap_atomic_idx();
#if HIGHMEM_DEBUG
{
@@ -119,6 +119,8 @@ static inline void __kunmap_atomic(unsig
__flush_tlb_one(vaddr);
}
#endif
+
+ kmap_atomic_idx_pop();
pagefault_enable();
}
#endif /* __KERNEL__ */
Index: linux-2.6/arch/powerpc/mm/highmem.c
===================================================================
--- linux-2.6.orig/arch/powerpc/mm/highmem.c
+++ linux-2.6/arch/powerpc/mm/highmem.c
@@ -62,7 +62,7 @@ void __kunmap_atomic(void *kvaddr)
return;
}
- type = kmap_atomic_idx_pop();
+ type = kmap_atomic_idx();
#ifdef CONFIG_DEBUG_HIGHMEM
{
@@ -79,6 +79,8 @@ void __kunmap_atomic(void *kvaddr)
local_flush_tlb_page(NULL, vaddr);
}
#endif
+
+ kmap_atomic_idx_pop();
pagefault_enable();
}
EXPORT_SYMBOL(__kunmap_atomic);
Index: linux-2.6/arch/sparc/mm/highmem.c
===================================================================
--- linux-2.6.orig/arch/sparc/mm/highmem.c
+++ linux-2.6/arch/sparc/mm/highmem.c
@@ -75,7 +75,7 @@ void __kunmap_atomic(void *kvaddr)
return;
}
- type = kmap_atomic_idx_pop();
+ type = kmap_atomic_idx();
#ifdef CONFIG_DEBUG_HIGHMEM
{
@@ -104,6 +104,8 @@ void __kunmap_atomic(void *kvaddr)
#endif
}
#endif
+
+ kmap_atomic_idx_pop();
pagefault_enable();
}
EXPORT_SYMBOL(__kunmap_atomic);
Index: linux-2.6/arch/tile/mm/highmem.c
===================================================================
--- linux-2.6.orig/arch/tile/mm/highmem.c
+++ linux-2.6/arch/tile/mm/highmem.c
@@ -241,7 +241,7 @@ void __kunmap_atomic(void *kvaddr)
pte_t pteval = *pte;
int idx, type;
- type = kmap_atomic_idx_pop();
+ type = kmap_atomic_idx();
idx = type + KM_TYPE_NR*smp_processor_id();
/*
@@ -252,6 +252,7 @@ void __kunmap_atomic(void *kvaddr)
BUG_ON(!pte_present(pteval) && !pte_migrating(pteval));
kmap_atomic_unregister(pte_page(pteval), vaddr);
kpte_clear_flush(pte, vaddr);
+ kmap_atomic_idx_pop();
} else {
/* Must be a lowmem page */
BUG_ON(vaddr < PAGE_OFFSET);
Index: linux-2.6/arch/x86/mm/highmem_32.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/highmem_32.c
+++ linux-2.6/arch/x86/mm/highmem_32.c
@@ -74,7 +74,7 @@ void __kunmap_atomic(void *kvaddr)
vaddr <= __fix_to_virt(FIX_KMAP_BEGIN)) {
int idx, type;
- type = kmap_atomic_idx_pop();
+ type = kmap_atomic_idx();
idx = type + KM_TYPE_NR * smp_processor_id();
#ifdef CONFIG_DEBUG_HIGHMEM
@@ -87,6 +87,7 @@ void __kunmap_atomic(void *kvaddr)
* attributes or becomes a protected page in a hypervisor.
*/
kpte_clear_flush(kmap_pte-idx, vaddr);
+ kmap_atomic_idx_pop();
}
#ifdef CONFIG_DEBUG_HIGHMEM
else {
Index: linux-2.6/arch/x86/mm/iomap_32.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/iomap_32.c
+++ linux-2.6/arch/x86/mm/iomap_32.c
@@ -98,7 +98,7 @@ iounmap_atomic(void __iomem *kvaddr)
vaddr <= __fix_to_virt(FIX_KMAP_BEGIN)) {
int idx, type;
- type = kmap_atomic_idx_pop();
+ type = kmap_atomic_idx();
idx = type + KM_TYPE_NR * smp_processor_id();
#ifdef CONFIG_DEBUG_HIGHMEM
@@ -111,6 +111,7 @@ iounmap_atomic(void __iomem *kvaddr)
* attributes or becomes a protected page in a hypervisor.
*/
kpte_clear_flush(kmap_pte-idx, vaddr);
+ kmap_atomic_idx_pop();
}
pagefault_enable();
Index: linux-2.6/include/linux/highmem.h
===================================================================
--- linux-2.6.orig/include/linux/highmem.h
+++ linux-2.6/include/linux/highmem.h
@@ -88,6 +88,11 @@ static inline int kmap_atomic_idx_push(v
return idx;
}
+static inline int kmap_atomic_idx(void)
+{
+ return __get_cpu_var(__kmap_atomic_idx) - 1;
+}
+
static inline int kmap_atomic_idx_pop(void)
{
int idx = --__get_cpu_var(__kmap_atomic_idx);
--
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