diff mbox series

mm/vmalloc: allow mem_dump_obj() to be called in interrupt context

Message ID 20221112121537.1634-1-thunder.leizhen@huawei.com
State New
Headers
Series mm/vmalloc: allow mem_dump_obj() to be called in interrupt context |

Commit Message

Zhen Lei Nov. 12, 2022, 12:15 p.m. UTC 
  The function mem_dump_obj() can sometimes provide valuable debugging
information, but it cannot be called in an interrupt context because
spinlock vmap_area_lock has not been protected against IRQs. If the
current task has held the lock before hard/soft interrupt handler calls
mem_dump_obj(), simply abandoning the dump operation can avoid deadlock.
That is, no deadlock occurs in extreme cases, and dump succeeds in most
cases.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 mm/vmalloc.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Andrew Morton Nov. 15, 2022, 12:54 a.m. UTC | #1 
On Sat, 12 Nov 2022 20:15:37 +0800 Zhen Lei <thunder.leizhen@huawei.com> wrote:

> The function mem_dump_obj() can sometimes provide valuable debugging
> information, but it cannot be called in an interrupt context because
> spinlock vmap_area_lock has not been protected against IRQs. If the
> current task has held the lock before hard/soft interrupt handler calls
> mem_dump_obj(), simply abandoning the dump operation can avoid deadlock.
> That is, no deadlock occurs in extreme cases, and dump succeeds in most
> cases.
> 
> ...
>
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -4034,6 +4034,9 @@ bool vmalloc_dump_obj(void *object)
>  	struct vm_struct *vm;
>  	void *objp = (void *)PAGE_ALIGN((unsigned long)object);
>  
> +	if (unlikely(spin_is_locked(&vmap_area_lock)))
> +		return false;
> +
>  	vm = find_vm_area(objp);
>  	if (!vm)
>  		return false;

Yes, but this will worsen the current uses of this function.  Consider
the case where task A wants to call vmalloc_dump_obj() but task B holds
vmap_area_lock.  No problem, task A will simply spin until task B is
done.

But after this patch, task A's call to vmalloc_dump_obj() will return
without having done anything.
diff mbox series

Patch

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ccaa461998f3c37..cdd36c5a1aa16f8 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4034,6 +4034,9 @@  bool vmalloc_dump_obj(void *object)
 	struct vm_struct *vm;
 	void *objp = (void *)PAGE_ALIGN((unsigned long)object);
 
+	if (unlikely(spin_is_locked(&vmap_area_lock)))
+		return false;
+
 	vm = find_vm_area(objp);
 	if (!vm)
 		return false;