Commit 42288fe3 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
Browse files

mm: mempolicy: Convert shared_policy mutex to spinlock 



Sasha was fuzzing with trinity and reported the following problem:

  BUG: sleeping function called from invalid context at kernel/mutex.c:269
  in_atomic(): 1, irqs_disabled(): 0, pid: 6361, name: trinity-main
  2 locks held by trinity-main/6361:
   #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff810aa314>] __do_page_fault+0x1e4/0x4f0
   #1:  (&(&mm->page_table_lock)->rlock){+.+...}, at: [<ffffffff8122f017>] handle_pte_fault+0x3f7/0x6a0
  Pid: 6361, comm: trinity-main Tainted: G        W
  3.7.0-rc2-next-20121024-sasha-00001-gd95ef01-dirty #74
  Call Trace:
    __might_sleep+0x1c3/0x1e0
    mutex_lock_nested+0x29/0x50
    mpol_shared_policy_lookup+0x2e/0x90
    shmem_get_policy+0x2e/0x30
    get_vma_policy+0x5a/0xa0
    mpol_misplaced+0x41/0x1d0
    handle_pte_fault+0x465/0x6a0

This was triggered by a different version of automatic NUMA balancing
but in theory the current version is vunerable to the same problem.

do_numa_page
  -> numa_migrate_prep
    -> mpol_misplaced
      -> get_vma_policy
        -> shmem_get_policy

It's very unlikely this will happen as shared pages are not marked
pte_numa -- see the page_mapcount() check in change_pte_range() -- but
it is possible.

To address this, this patch restores sp->lock as originally implemented
by Kosaki Motohiro.  In the path where get_vma_policy() is called, it
should not be calling sp_alloc() so it is not necessary to treat the PTL
specially.

Signed-off-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Tested-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5439ca6b

include/linux/mempolicy.h

+1 −1
Original line number Diff line number Diff line
@@ -123,7 +123,7 @@ struct sp_node { 


struct shared_policy {

	struct rb_root root;

	struct mutex mutex;

	spinlock_t lock;

};



void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol);

mm/mempolicy.c

+48 −20
Original line number Diff line number Diff line
@@ -2132,7 +2132,7 @@ bool __mpol_equal(struct mempolicy *a, struct mempolicy *b) 
 */



/* lookup first element intersecting start-end */

/* Caller holds sp->mutex */

/* Caller holds sp->lock */

static struct sp_node *

sp_lookup(struct shared_policy *sp, unsigned long start, unsigned long end)

{
@@ -2196,13 +2196,13 @@ mpol_shared_policy_lookup(struct shared_policy *sp, unsigned long idx) 


	if (!sp->root.rb_node)

		return NULL;

	mutex_lock(&sp->mutex);

	spin_lock(&sp->lock);

	sn = sp_lookup(sp, idx, idx+1);

	if (sn) {

		mpol_get(sn->policy);

		pol = sn->policy;

	}

	mutex_unlock(&sp->mutex);

	spin_unlock(&sp->lock);

	return pol;

}
@@ -2328,6 +2328,14 @@ static void sp_delete(struct shared_policy *sp, struct sp_node *n) 
	sp_free(n);

}



static void sp_node_init(struct sp_node *node, unsigned long start,

			unsigned long end, struct mempolicy *pol)

{

	node->start = start;

	node->end = end;

	node->policy = pol;

}



static struct sp_node *sp_alloc(unsigned long start, unsigned long end,

				struct mempolicy *pol)

{
@@ -2344,10 +2352,7 @@ static struct sp_node *sp_alloc(unsigned long start, unsigned long end, 
		return NULL;

	}

	newpol->flags |= MPOL_F_SHARED;



	n->start = start;

	n->end = end;

	n->policy = newpol;

	sp_node_init(n, start, end, newpol);



	return n;

}
@@ -2357,9 +2362,12 @@ static int shared_policy_replace(struct shared_policy *sp, unsigned long start, 
				 unsigned long end, struct sp_node *new)

{

	struct sp_node *n;

	struct sp_node *n_new = NULL;

	struct mempolicy *mpol_new = NULL;

	int ret = 0;



	mutex_lock(&sp->mutex);

restart:

	spin_lock(&sp->lock);

	n = sp_lookup(sp, start, end);

	/* Take care of old policies in the same range. */

	while (n && n->start < end) {
@@ -2372,14 +2380,16 @@ 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) {

					ret = -ENOMEM;

					goto out;

				}

				if (!n_new)

					goto alloc_new;



				*mpol_new = *n->policy;

				atomic_set(&mpol_new->refcnt, 1);

				sp_node_init(n_new, n->end, end, mpol_new);

				sp_insert(sp, n_new);

				n->end = start;

				sp_insert(sp, new2);

				n_new = NULL;

				mpol_new = NULL;

				break;

			} else

				n->end = start;
@@ -2390,9 +2400,27 @@ static int shared_policy_replace(struct shared_policy *sp, unsigned long start, 
	}

	if (new)

		sp_insert(sp, new);

out:

	mutex_unlock(&sp->mutex);

	spin_unlock(&sp->lock);

	ret = 0;



err_out:

	if (mpol_new)

		mpol_put(mpol_new);

	if (n_new)

		kmem_cache_free(sn_cache, n_new);



	return ret;



alloc_new:

	spin_unlock(&sp->lock);

	ret = -ENOMEM;

	n_new = kmem_cache_alloc(sn_cache, GFP_KERNEL);

	if (!n_new)

		goto err_out;

	mpol_new = kmem_cache_alloc(policy_cache, GFP_KERNEL);

	if (!mpol_new)

		goto err_out;

	goto restart;

}



/**
@@ -2410,7 +2438,7 @@ void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol) 
	int ret;



	sp->root = RB_ROOT;		/* empty tree == default mempolicy */

	mutex_init(&sp->mutex);

	spin_lock_init(&sp->lock);



	if (mpol) {

		struct vm_area_struct pvma;
@@ -2476,14 +2504,14 @@ void mpol_free_shared_policy(struct shared_policy *p) 


	if (!p->root.rb_node)

		return;

	mutex_lock(&p->mutex);

	spin_lock(&p->lock);

	next = rb_first(&p->root);

	while (next) {

		n = rb_entry(next, struct sp_node, nd);

		next = rb_next(&n->nd);

		sp_delete(p, n);

	}

	mutex_unlock(&p->mutex);

	spin_unlock(&p->lock);

}



#ifdef CONFIG_NUMA_BALANCING

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