From a8dcd6bf2f67f75df0112886ffbd3528fb515609 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Thu, 13 Sep 2012 10:58:33 +1000 Subject: [PATCH] mempolicy: fix a race in shared_policy_replace() 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 Acked-by: KOSAKI Motohiro Reviewed-by: Christoph Lameter Cc: Josh Boyer Signed-off-by: Andrew Morton --- include/linux/mempolicy.h | 2 +- mm/mempolicy.c | 37 ++++++++++++++++--------------------- 2 files changed, 17 insertions(+), 22 deletions(-) diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h index ba7a0ff19d39..cec569325608 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 f0728ae74672..b2f12ecc1b34 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -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 @@ 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; @@ -2229,12 +2227,9 @@ 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; } /** @@ -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 */ -- 2.39.5