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mempolicy: fix a race in shared_policy_replace()

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shared_policy_replace() use of sp_alloc() is unsafe.  1) sp_node cannot
be dereferenced if sp->lock is not held and 2) another thread can modify
sp_node between spin_unlock for allocating a new sp node and next
spin_lock.  The bug was introduced before 2.6.12-rc2.

Kosaki's original patch for this problem was to allocate an sp node and
policy within shared_policy_replace and initialise it when the lock is
reacquired.  I was not keen on this approach because it partially
duplicates sp_alloc().  As the paths were sp->lock is taken are not that
performance critical this patch converts sp->lock to sp->mutex so it can
sleep when calling sp_alloc().

[kosaki.motohiro@jp.fujitsu.com: Original patch]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Christoph Lameter <cl@linux.com>
Cc: Josh Boyer <jwboyer@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mel Gorman 2012-10-08 16:29:17 -07:00 committed by Linus Torvalds
parent 869833f2c5
commit b22d127a39
2 changed files with 17 additions and 22 deletions
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2
include/linux/mempolicy.h
View File

@ -188,7 +188,7 @@ struct sp_node {
struct shared_policy {
struct rb_root root;
spinlock_t lock;
struct mutex mutex;
};
void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol);

37
mm/mempolicy.c
View File

@ -2083,7 +2083,7 @@ bool __mpol_equal(struct mempolicy *a, struct mempolicy *b)
*/
/* lookup first element intersecting start-end */
/* Caller holds sp->lock */
/* Caller holds sp->mutex */
static struct sp_node *
sp_lookup(struct shared_policy *sp, unsigned long start, unsigned long end)
{
@ -2147,13 +2147,13 @@ mpol_shared_policy_lookup(struct shared_policy *sp, unsigned long idx)
if (!sp->root.rb_node)
return NULL;
spin_lock(&sp->lock);
mutex_lock(&sp->mutex);
sn = sp_lookup(sp, idx, idx+1);
if (sn) {
mpol_get(sn->policy);
pol = sn->policy;
}
spin_unlock(&sp->lock);
mutex_unlock(&sp->mutex);
return pol;
}
@ -2193,10 +2193,10 @@ static struct sp_node *sp_alloc(unsigned long start, unsigned long end,
static int shared_policy_replace(struct shared_policy *sp, unsigned long start,
unsigned long end, struct sp_node *new)
{
struct sp_node *n, *new2 = NULL;
struct sp_node *n;
int ret = 0;
restart:
spin_lock(&sp->lock);
mutex_lock(&sp->mutex);
n = sp_lookup(sp, start, end);
/* Take care of old policies in the same range. */
while (n && n->start < end) {
@ -2209,16 +2209,14 @@ static int shared_policy_replace(struct shared_policy *sp, unsigned long start,
} else {
/* Old policy spanning whole new range. */
if (n->end > end) {
struct sp_node *new2;
new2 = sp_alloc(end, n->end, n->policy);
if (!new2) {
spin_unlock(&sp->lock);
new2 = sp_alloc(end, n->end, n->policy);
if (!new2)
return -ENOMEM;
goto restart;
ret = -ENOMEM;
goto out;
}
n->end = start;
sp_insert(sp, new2);
new2 = NULL;
break;
} else
n->end = start;
@ -2229,12 +2227,9 @@ static int shared_policy_replace(struct shared_policy *sp, unsigned long start,
}
if (new)
sp_insert(sp, new);
spin_unlock(&sp->lock);
if (new2) {
mpol_put(new2->policy);
kmem_cache_free(sn_cache, new2);
}
return 0;
out:
mutex_unlock(&sp->mutex);
return ret;
}
/**
@ -2252,7 +2247,7 @@ void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol)
int ret;
sp->root = RB_ROOT; /* empty tree == default mempolicy */
spin_lock_init(&sp->lock);
mutex_init(&sp->mutex);
if (mpol) {
struct vm_area_struct pvma;
@ -2318,7 +2313,7 @@ void mpol_free_shared_policy(struct shared_policy *p)
if (!p->root.rb_node)
return;
spin_lock(&p->lock);
mutex_lock(&p->mutex);
next = rb_first(&p->root);
while (next) {
n = rb_entry(next, struct sp_node, nd);
@ -2327,7 +2322,7 @@ void mpol_free_shared_policy(struct shared_policy *p)
mpol_put(n->policy);
kmem_cache_free(sn_cache, n);
}
spin_unlock(&p->lock);
mutex_unlock(&p->mutex);
}
/* assumes fs == KERNEL_DS */