diff options
author | Mel Gorman <mgorman@suse.de> | 2012-10-08 16:29:17 -0700 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-10-13 05:38:56 +0900 |
commit | 04a30bd9dccbeee2cc6b035e42a37e9be0fa8c6c (patch) | |
tree | 8b8c631b4b951e9a1676464c8f033143b979f7ed | |
parent | 33efe2910bf7865a7d1fba4b06c9fa4b6fda6856 (diff) | |
download | lwn-04a30bd9dccbeee2cc6b035e42a37e9be0fa8c6c.tar.gz lwn-04a30bd9dccbeee2cc6b035e42a37e9be0fa8c6c.zip |
mempolicy: fix a race in shared_policy_replace()
commit b22d127a39ddd10d93deee3d96e643657ad53a49 upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | include/linux/mempolicy.h | 2 | ||||
-rw-r--r-- | mm/mempolicy.c | 37 |
2 files changed, 17 insertions, 22 deletions
diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h index 7c727a90d70d..0abf1d436b12 100644 --- a/include/linux/mempolicy.h +++ b/include/linux/mempolicy.h @@ -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); diff --git a/mm/mempolicy.c b/mm/mempolicy.c index c2efa3ddf62b..30850253c06c 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2057,7 +2057,7 @@ 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) { @@ -2121,13 +2121,13 @@ 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; } @@ -2167,10 +2167,10 @@ 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) { @@ -2183,16 +2183,14 @@ restart: } 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; @@ -2203,12 +2201,9 @@ restart: } 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; } /** @@ -2226,7 +2221,7 @@ 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; @@ -2292,7 +2287,7 @@ 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); @@ -2301,7 +2296,7 @@ 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 */ |