[patch 4/4] vunmap: Fix racy use of rcu_head

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

[-- Attachment #1: vunmap-fix-teardown.patch --]
[-- Type: text/plain, Size: 3613 bytes --]

Repetitive use of vmap/vunmap on the same address triggers this bug.

Simplest fix: directly kfree the data structure rather than doing it lazily.

Impact:
(-) slight slowdown on vunmap
(+) stop messing up rcu callback lists ;)

Caught it with DEBUG_RCU_HEAD, running LTTng armall/disarmall in loops.
Immediate values (with breakpoint-ipi scheme) are still using vunmap.

------------[ cut here ]------------
WARNING: at kernel/rcutree.c:1199 __call_rcu+0x181/0x190()
Hardware name: X7DAL
Modules linked in: loop ltt_statedump ltt_userspace_event ipc_tr]
Pid: 4527, comm: ltt-armall Not tainted 2.6.30.9-trace #30
Call Trace:
 [<ffffffff8027b181>] ? __call_rcu+0x181/0x190
 [<ffffffff8027b181>] ? __call_rcu+0x181/0x190
 [<ffffffff8023a6a9>] ? warn_slowpath_common+0x79/0xd0
 [<ffffffff802b4890>] ? rcu_free_va+0x0/0x10
 [<ffffffff8027b181>] ? __call_rcu+0x181/0x190
 [<ffffffff802b5298>] ? __purge_vmap_area_lazy+0x1a8/0x1e0
 [<ffffffff802b59d4>] ? free_unmap_vmap_area_noflush+0x74/0x80
 [<ffffffff802b5a0e>] ? remove_vm_area+0x2e/0x80
 [<ffffffff802b5b35>] ? __vunmap+0x45/0xf0
 [<ffffffffa002e826>] ? ltt_statedump_start+0x7b6/0x820 [ltt_sta]
 [<ffffffff8068978a>] ? arch_imv_update+0x16a/0x2f0
 [<ffffffff8027dd13>] ? imv_update_range+0x53/0xa0
 [<ffffffff8026235b>] ? _module_imv_update+0x4b/0x60
 [<ffffffff80262385>] ? module_imv_update+0x15/0x30
 [<ffffffff80280049>] ? marker_probe_register+0x149/0xb90
 [<ffffffff8040c8e0>] ? ltt_vtrace+0x0/0x8c0
 [<ffffffff80409330>] ? ltt_marker_connect+0xd0/0x150
 [<ffffffff8040f8dc>] ? marker_enable_write+0xec/0x120
 [<ffffffff802c6cb8>] ? __dentry_open+0x268/0x350
 [<ffffffff80280b2c>] ? marker_probe_cb+0x9c/0x170
 [<ffffffff80280b2c>] ? marker_probe_cb+0x9c/0x170
 [<ffffffff802c973b>] ? vfs_write+0xcb/0x170
 [<ffffffff802c9984>] ? sys_write+0x64/0x130
 [<ffffffff8020beeb>] ? system_call_fastpath+0x16/0x1b
---[ end trace ef92443e716fa199 ]---
------------[ cut here ]------------

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: cl@linux-foundation.org
CC: mingo@elte.hu
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: linux-mm@kvack.org
CC: akpm@linux-foundation.org
---
 mm/vmalloc.c |   18 ++----------------
 1 file changed, 2 insertions(+), 16 deletions(-)

Index: linux-2.6-lttng/mm/vmalloc.c
===================================================================
--- linux-2.6-lttng.orig/mm/vmalloc.c	2009-10-06 09:37:04.000000000 -0400
+++ linux-2.6-lttng/mm/vmalloc.c	2009-10-06 09:37:56.000000000 -0400
@@ -417,13 +417,6 @@ overflow:
 	return va;
 }
 
-static void rcu_free_va(struct rcu_head *head)
-{
-	struct vmap_area *va = container_of(head, struct vmap_area, rcu_head);
-
-	kfree(va);
-}
-
 static void __free_vmap_area(struct vmap_area *va)
 {
 	BUG_ON(RB_EMPTY_NODE(&va->rb_node));
@@ -431,7 +424,7 @@ static void __free_vmap_area(struct vmap
 	RB_CLEAR_NODE(&va->rb_node);
 	list_del_rcu(&va->list);
 
-	call_rcu(&va->rcu_head, rcu_free_va);
+	kfree(va);
 }
 
 /*
@@ -757,13 +750,6 @@ static struct vmap_block *new_vmap_block
 	return vb;
 }
 
-static void rcu_free_vb(struct rcu_head *head)
-{
-	struct vmap_block *vb = container_of(head, struct vmap_block, rcu_head);
-
-	kfree(vb);
-}
-
 static void free_vmap_block(struct vmap_block *vb)
 {
 	struct vmap_block *tmp;
@@ -778,7 +764,7 @@ static void free_vmap_block(struct vmap_
 	BUG_ON(tmp != vb);
 
 	free_unmap_vmap_area_noflush(vb->va);
-	call_rcu(&vb->rcu_head, rcu_free_vb);
+	kfree(vb);
 }
 
 static void *vb_alloc(unsigned long size, gfp_t gfp_mask)

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68