[PATCH] rcu: Make vmalloc_dump_obj() call in a preemptible context

[Zqiang]

Currently, the mem_dump_obj() is invoked in call_rcu(), the
call_rcu() is maybe invoked in non-preemptive code segment,
for object allocated from vmalloc(), the following scenarios
may occur:

	CPU 0
tasks context
   spin_lock(&vmap_area_lock)
          Interrupt context
	      call_rcu()
		mem_dump_obj
                  vmalloc_dump_obj
                    spin_lock(&vmap_area_lock) <--deadlock

and for PREEMPT-RT kernel, the spinlock will convert to sleepable
lock, it also make vmap_area_lock spinlock can not acquire in
non-preemptive code segment. therefore, this commit make the
vmalloc_dump_obj() call in a preemptible context.

Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
---
 mm/util.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 12984e76767e..465f8b8824ca 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1124,8 +1124,12 @@ void mem_dump_obj(void *object)
 		return;
 	}
 
-	if (vmalloc_dump_obj(object))
-		return;
+	if (is_vmalloc_addr(object)) {
+		if (preemptible() && vmalloc_dump_obj(object))
+			return;
+		type = "vmalloc memory";
+		goto end;
+	}
 
 	if (virt_addr_valid(object))
 		type = "non-slab/vmalloc memory";
@@ -1135,7 +1139,7 @@ void mem_dump_obj(void *object)
 		type = "zero-size pointer";
 	else
 		type = "non-paged memory";
-
+end:
 	pr_cont(" %s\n", type);
 }
 EXPORT_SYMBOL_GPL(mem_dump_obj);
-- 
2.25.1