[PATCH v3] mm: Make vmalloc_dump_obj() call in clean 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, so the vmap_area_lock spinlock not allowed to get in non-preemptive
code segment. therefore, this commit make the vmalloc_dump_obj() call in
a clean context.

Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
---
 v1->v2:
 add IS_ENABLED(CONFIG_PREEMPT_RT) check.
 v2->v3:
 change commit message and add some comment.

 mm/util.c    |  4 +++-
 mm/vmalloc.c | 25 +++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/mm/util.c b/mm/util.c
index 12984e76767e..2b0222a728cc 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1128,7 +1128,9 @@ void mem_dump_obj(void *object)
 		return;
 
 	if (virt_addr_valid(object))
-		type = "non-slab/vmalloc memory";
+		type = "non-slab memory";
+	else if (is_vmalloc_addr(object))
+		type = "vmalloc memory";
 	else if (object == NULL)
 		type = "NULL pointer";
 	else if (object == ZERO_SIZE_PTR)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ccaa461998f3..4351eafbe7ab 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4034,6 +4034,31 @@ bool vmalloc_dump_obj(void *object)
 	struct vm_struct *vm;
 	void *objp = (void *)PAGE_ALIGN((unsigned long)object);
 
+	/* for non-vmalloc addr, return directly */
+	if (!is_vmalloc_addr(objp))
+		return false;
+
+	/**
+	 * for non-Preempt-RT kernel, return directly. otherwise not
+	 * only needs to determine whether it is in the interrupt context
+	 * (in_interrupt())to avoid deadlock, but also to avoid acquire
+	 * vmap_area_lock spinlock in disables interrupts or preempts
+	 * critical sections, because the vmap_area_lock spinlock convert
+	 * to sleepable lock
+	 */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && !preemptible())
+		return false;
+
+	/**
+	 * get here, for Preempt-RT kernel, it means that we are in
+	 * preemptible context(preemptible() is true), it also means
+	 * that the in_interrupt() will return false.
+	 * for non-Preempt-RT kernel, only needs to determine whether
+	 * it is in the interrupt context(in_interrupt()) to avoid deadlock
+	 */
+	if (in_interrupt())
+		return false;
+
 	vm = find_vm_area(objp);
 	if (!vm)
 		return false;
-- 
2.25.1