A lockdep reports a possible deadlock in the find_vmap_area_exceed_addr_lock()
function:
============================================
WARNING: possible recursive locking detected
6.9.0-rc1-00060-ged3ccc57b108-dirty #6140 Not tainted
--------------------------------------------
drgn/455 is trying to acquire lock:
ffff0000c00131d0 (&vn->busy.lock/1){+.+.}-{2:2}, at: find_vmap_area_exceed_addr_lock+0x64/0x124
but task is already holding lock:
ffff0000c0011878 (&vn->busy.lock/1){+.+.}-{2:2}, at: find_vmap_area_exceed_addr_lock+0x64/0x124
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&vn->busy.lock/1);
lock(&vn->busy.lock/1);
*** DEADLOCK ***
indeed it can happen if the find_vmap_area_exceed_addr_lock()
gets called concurrently because it tries to acquire two nodes
locks. It was done to prevent removing a lowest VA found on a
previous step.
To address this a lowest VA is found first without holding a
node lock where it resides. As a last step we check if a VA
still there because it can go away, if removed, proceed with
next lowest.
Fixes: 53becf32aec1 ("mm: vmalloc: support multiple nodes in vread_iter")
Tested-by: Jens Axboe <axboe@xxxxxxxxx>
Tested-by: Omar Sandoval <osandov@xxxxxx>
Reported-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
---
mm/vmalloc.c | 74 +++++++++++++++++++++++++++++++---------------------
1 file changed, 44 insertions(+), 30 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index e94ce4562805..a5a5dfc3843e 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -989,6 +989,27 @@ unsigned long vmalloc_nr_pages(void)
return atomic_long_read(&nr_vmalloc_pages);
}
+static struct vmap_area *__find_vmap_area(unsigned long addr, struct rb_root *root)
+{
+ struct rb_node *n = root->rb_node;
+
+ addr = (unsigned long)kasan_reset_tag((void *)addr);
+
+ while (n) {
+ struct vmap_area *va;
+
+ va = rb_entry(n, struct vmap_area, rb_node);
+ if (addr < va->va_start)
+ n = n->rb_left;
+ else if (addr >= va->va_end)
+ n = n->rb_right;
+ else
+ return va;
+ }
+
+ return NULL;
+}
+
/* Look up the first VA which satisfies addr < va_end, NULL if none. */
static struct vmap_area *
__find_vmap_area_exceed_addr(unsigned long addr, struct rb_root *root)
@@ -1025,47 +1046,40 @@ __find_vmap_area_exceed_addr(unsigned long addr, struct rb_root *root)
static struct vmap_node *
find_vmap_area_exceed_addr_lock(unsigned long addr, struct vmap_area **va)
{
- struct vmap_node *vn, *va_node = NULL;
- struct vmap_area *va_lowest;
+ unsigned long va_start_lowest;
+ struct vmap_node *vn;
int i;
- for (i = 0; i < nr_vmap_nodes; i++) {
+repeat:
+ for (i = 0, va_start_lowest = 0; i < nr_vmap_nodes; i++) {
vn = &vmap_nodes[i];
spin_lock(&vn->busy.lock);
- va_lowest = __find_vmap_area_exceed_addr(addr, &vn->busy.root);
- if (va_lowest) {
- if (!va_node || va_lowest->va_start < (*va)->va_start) {
- if (va_node)
- spin_unlock(&va_node->busy.lock);
-
- *va = va_lowest;
- va_node = vn;
- continue;
- }
- }
+ *va = __find_vmap_area_exceed_addr(addr, &vn->busy.root);
+
+ if (*va)
+ if (!va_start_lowest || (*va)->va_start < va_start_lowest)
+ va_start_lowest = (*va)->va_start;
spin_unlock(&vn->busy.lock);
}
- return va_node;
-}
-
-static struct vmap_area *__find_vmap_area(unsigned long addr, struct rb_root *root)
-{
- struct rb_node *n = root->rb_node;
+ /*
+ * Check if found VA exists, it might it is gone away.
+ * In this case we repeat the search because a VA has
+ * been removed concurrently thus we need to proceed
+ * with next one what is a rare case.
+ */
+ if (va_start_lowest) {
+ vn = addr_to_node(va_start_lowest);
- addr = (unsigned long)kasan_reset_tag((void *)addr);
+ spin_lock(&vn->busy.lock);
+ *va = __find_vmap_area(va_start_lowest, &vn->busy.root);
- while (n) {
- struct vmap_area *va;
+ if (*va)
+ return vn;
- va = rb_entry(n, struct vmap_area, rb_node);
- if (addr < va->va_start)
- n = n->rb_left;
- else if (addr >= va->va_end)
- n = n->rb_right;
- else
- return va;
+ spin_unlock(&vn->busy.lock);
+ goto repeat;
}
return NULL;
--
2.39.2
