On Fri, Jun 14, 2024 at 6:57 PM Catalin Marinas [off-list ref] wrote:

On Thu, Jun 13, 2024 at 08:10:17PM +0800, Yafang Shao wrote:

quoted

On Thu, Jun 13, 2024 at 4:37 PM Catalin Marinas [off-list ref] wrote:

quoted

On Thu, Jun 13, 2024 at 10:30:40AM +0800, Yafang Shao wrote:

quoted

Using __get_task_comm() to read the task comm ensures that the name is
always NUL-terminated, regardless of the source string. This approach also
facilitates future extensions to the task comm.

Signed-off-by: Yafang Shao <redacted>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 mm/kmemleak.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index d5b6fba44fc9..ef29aaab88a0 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c

@@ -663,13 +663,7 @@ static struct kmemleak_object *__alloc_object(gfp_t gfp)
              strncpy(object->comm, "softirq", sizeof(object->comm));
      } else {
              object->pid = current->pid;
-             /*
-              * There is a small chance of a race with set_task_comm(),
-              * however using get_task_comm() here may cause locking
-              * dependency issues with current->alloc_lock. In the worst
-              * case, the command line is not correct.
-              */
-             strncpy(object->comm, current->comm, sizeof(object->comm));
+             __get_task_comm(object->comm, sizeof(object->comm), current);
      }

You deleted the comment stating why it does not use get_task_comm()
without explaining why it would be safe now. I don't recall the details
but most likely lockdep warned of some potential deadlocks with this
function being called with the task_lock held.

So, you either show why this is safe or just use strscpy() directly here
(not sure we'd need strscpy_pad(); I think strscpy() would do, we just
need the NUL-termination).

The task_lock was dropped in patch #1 [0]. My apologies for not
including you in the CC for that change. After this modification, it
is now safe to use __get_task_comm().

[0] https://lore.kernel.org/all/20240613023044.45873-2-laoar.shao@gmail.com/ (local)

Ah, great. For this patch:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

You may want to add a comment in the commit log that since
__get_task_comm() no longer takes a long, it's safe to call it from
kmemleak.

I will add it. Thanks for your suggestion.

-- 
Regards
Yafang