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Date: Fri, 23 Apr 2010 12:01:48 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: "linux-mm@...ck.org" <linux-mm@...ck.org>
Cc: Mel Gorman <mel@....ul.ie>,
"minchan.kim@...il.com" <minchan.kim@...il.com>,
Christoph Lameter <cl@...ux.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [BUGFIX][mm][PATCH] fix migration race in rmap_walk
This patch itself is for -mm ..but may need to go -stable tree for memory
hotplug. (but we've got no report to hit this race...)
This one is the simplest, I think and works well on my test set.
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
In rmap.c, at checking rmap in vma chain in page->mapping, anon_vma->lock
or mapping->i_mmap_lock is held and enter following loop.
for_each_vma_in_this_rmap_link(list from page->mapping) {
unsigned long address = vma_address(page, vma);
if (address == -EFAULT)
continue;
....
}
vma_address is checking [start, end, pgoff] v.s. page->index.
But vma's [start, end, pgoff] is updated without locks. vma_address()
can hit a race and may return wrong result.
This bahavior is no problem in usual routine as try_to_unmap() etc...
But for page migration, rmap_walk() has to find all migration_ptes
which migration code overwritten valid ptes. This race is critical and cause
BUG that a migration_pte is sometimes not removed.
pr 21 17:27:47 localhost kernel: ------------[ cut here ]------------
Apr 21 17:27:47 localhost kernel: kernel BUG at include/linux/swapops.h:105!
Apr 21 17:27:47 localhost kernel: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC
Apr 21 17:27:47 localhost kernel: last sysfs file: /sys/devices/virtual/net/br0/statistics/collisions
Apr 21 17:27:47 localhost kernel: CPU 3
Apr 21 17:27:47 localhost kernel: Modules linked in: fuse sit tunnel4 ipt_MASQUERADE iptable_nat nf_nat bridge stp llc sunrpc cpufreq_ondemand acpi_cpufreq freq_table mperf xt_physdev ip6t_REJECT nf_conntrack_ipv6 ip6table_filter ip6_tables ipv6 dm_multipath uinput ioatdma ppdev parport_pc i5000_edac bnx2 iTCO_wdt edac_core iTCO_vendor_support shpchp parport e1000e kvm_intel dca kvm i2c_i801 i2c_core i5k_amb pcspkr megaraid_sas [last unloaded: microcode]
Apr 21 17:27:47 localhost kernel:
Apr 21 17:27:47 localhost kernel: Pid: 27892, comm: cc1 Tainted: G W 2.6.34-rc4-mm1+ #4 D2519/PRIMERGY
Apr 21 17:27:47 localhost kernel: RIP: 0010:[<ffffffff8114e9cf>] [<ffffffff8114e9cf>] migration_entry_wait+0x16f/0x180
Apr 21 17:27:47 localhost kernel: RSP: 0000:ffff88008d9efe08 EFLAGS: 00010246
Apr 21 17:27:47 localhost kernel: RAX: ffffea0000000000 RBX: ffffea0000241100 RCX: 0000000000000001
Apr 21 17:27:47 localhost kernel: RDX: 000000000000a4e0 RSI: ffff880621a4ab00 RDI: 000000000149c03e
Apr 21 17:27:47 localhost kernel: RBP: ffff88008d9efe38 R08: 0000000000000000 R09: 0000000000000000
Apr 21 17:27:47 localhost kernel: R10: 0000000000000000 R11: 0000000000000001 R12: ffff880621a4aae8
Apr 21 17:27:47 localhost kernel: R13: 00000000bf811000 R14: 000000000149c03e R15: 0000000000000000
Apr 21 17:27:47 localhost kernel: FS: 00007fe6abc90700(0000) GS:ffff880005a00000(0000) knlGS:0000000000000000
Apr 21 17:27:47 localhost kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Apr 21 17:27:47 localhost kernel: CR2: 00007fe6a37279a0 CR3: 000000008d942000 CR4: 00000000000006e0
Apr 21 17:27:47 localhost kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Apr 21 17:27:47 localhost kernel: DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Apr 21 17:27:47 localhost kernel: Process cc1 (pid: 27892, threadinfo ffff88008d9ee000, task ffff8800b23ec820)
Apr 21 17:27:47 localhost kernel: Stack:
Apr 21 17:27:47 localhost kernel: ffffea000101aee8 ffff880621a4aae8 ffff88008d9efe38 00007fe6a37279a0
Apr 21 17:27:47 localhost kernel: <0> ffff8805d9706d90 ffff880621a4aa00 ffff88008d9efef8 ffffffff81126d05
Apr 21 17:27:47 localhost kernel: <0> ffff88008d9efec8 0000000000000246 0000000000000000 ffffffff81586533
Apr 21 17:27:47 localhost kernel: Call Trace:
Apr 21 17:27:47 localhost kernel: [<ffffffff81126d05>] handle_mm_fault+0x995/0x9b0
Apr 21 17:27:47 localhost kernel: [<ffffffff81586533>] ? do_page_fault+0x103/0x330
Apr 21 17:27:47 localhost kernel: [<ffffffff8104bf40>] ? finish_task_switch+0x0/0xf0
Apr 21 17:27:47 localhost kernel: [<ffffffff8158659e>] do_page_fault+0x16e/0x330
Apr 21 17:27:47 localhost kernel: [<ffffffff81582f35>] page_fault+0x25/0x30
Apr 21 17:27:47 localhost kernel: Code: 53 08 85 c9 0f 84 32 ff ff ff 8d 41 01 89 4d d8 89 45 d4 8b 75 d4 8b 45 d8 f0 0f b1 32 89 45 dc 8b 45 dc 39 c8 74 aa 89 c1 eb d7 <0f> 0b eb fe 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5
Apr 21 17:27:47 localhost kernel: RIP [<ffffffff8114e9cf>] migration_entry_wait+0x16f/0x180
Apr 21 17:27:47 localhost kernel: RSP <ffff88008d9efe08>
Apr 21 17:27:47 localhost kernel: ---[ end trace 4860ab585c1fcddb ]---
This patch adds vma_address_safe(). And update [start, end, pgoff]
under seq counter.
Cc: Mel Gorman <mel@....ul.ie>
Cc: Minchan Kim <minchan.kim@...il.com>
Cc: Christoph Lameter <cl@...ux-foundation.org>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
include/linux/mm_types.h | 2 ++
mm/mmap.c | 15 ++++++++++++++-
mm/rmap.c | 25 ++++++++++++++++++++++++-
3 files changed, 40 insertions(+), 2 deletions(-)
Index: linux-2.6.34-rc5-mm1/include/linux/mm_types.h
===================================================================
--- linux-2.6.34-rc5-mm1.orig/include/linux/mm_types.h
+++ linux-2.6.34-rc5-mm1/include/linux/mm_types.h
@@ -12,6 +12,7 @@
#include <linux/completion.h>
#include <linux/cpumask.h>
#include <linux/page-debug-flags.h>
+#include <linux/seqlock.h>
#include <asm/page.h>
#include <asm/mmu.h>
@@ -183,6 +184,7 @@ struct vm_area_struct {
#ifdef CONFIG_NUMA
struct mempolicy *vm_policy; /* NUMA policy for the VMA */
#endif
+ seqcount_t updating; /* works like seqlock for updating vma info. */
};
struct core_thread {
Index: linux-2.6.34-rc5-mm1/mm/mmap.c
===================================================================
--- linux-2.6.34-rc5-mm1.orig/mm/mmap.c
+++ linux-2.6.34-rc5-mm1/mm/mmap.c
@@ -491,6 +491,16 @@ __vma_unlink(struct mm_struct *mm, struc
mm->mmap_cache = prev;
}
+static void adjust_start_vma(struct vm_area_struct *vma)
+{
+ write_seqcount_begin(&vma->updating);
+}
+
+static void adjust_end_vma(struct vm_area_struct *vma)
+{
+ write_seqcount_end(&vma->updating);
+}
+
/*
* We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
* is already present in an i_mmap tree without adjusting the tree.
@@ -584,13 +594,16 @@ again: remove_next = 1 + (end > next->
if (adjust_next)
vma_prio_tree_remove(next, root);
}
-
+ adjust_start_vma(vma);
vma->vm_start = start;
vma->vm_end = end;
vma->vm_pgoff = pgoff;
+ adjust_end_vma(vma);
if (adjust_next) {
+ adjust_start_vma(next);
next->vm_start += adjust_next << PAGE_SHIFT;
next->vm_pgoff += adjust_next;
+ adjust_end_vma(next);
}
if (root) {
Index: linux-2.6.34-rc5-mm1/mm/rmap.c
===================================================================
--- linux-2.6.34-rc5-mm1.orig/mm/rmap.c
+++ linux-2.6.34-rc5-mm1/mm/rmap.c
@@ -342,6 +342,23 @@ vma_address(struct page *page, struct vm
}
/*
+ * vma's address check is racy if we don't hold mmap_sem. This function
+ * gives a safe way for accessing the [start, end, pgoff] tuple of vma.
+ */
+
+static inline unsigned long vma_address_safe(struct page *page,
+ struct vm_area_struct *vma)
+{
+ unsigned long ret, safety;
+
+ do {
+ safety = read_seqcount_begin(&vma->updating);
+ ret = vma_address(page, vma);
+ } while (read_seqcount_retry(&vma->updating, safety));
+ return ret;
+}
+
+/*
* At what user virtual address is page expected in vma?
* checking that the page matches the vma.
*/
@@ -1372,7 +1389,13 @@ static int rmap_walk_anon(struct page *p
spin_lock(&anon_vma->lock);
list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
struct vm_area_struct *vma = avc->vma;
- unsigned long address = vma_address(page, vma);
+ unsigned long address;
+
+ /*
+ * In page migration, this race is critical. So, use
+ * safe version.
+ */
+ address = vma_address_safe(page, vma);
if (address == -EFAULT)
continue;
ret = rmap_one(page, vma, address, arg);
--
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