[PATCH] mm/slub: use stackdepot to save stack trace in objects-fix

[Vlastimil Babka]

Paul reports [1] lockdep splat HARDIRQ-safe -> HARDIRQ-unsafe lock order detected.
Kernel test robot reports [2] BUG:sleeping_function_called_from_invalid_context_at_mm/page_alloc.c

The stack trace might be saved from contexts where we can't block so GFP_KERNEL
is unsafe. So Use GFP_NOWAIT. Under memory pressure we might thus fail to save
some new unique stack, but that should be extremely rare.

[1] https://lore.kernel.org/linux-mm/20210515204622.GA2672367@paulmck-ThinkPad-P17-Gen-1/
[2] https://lore.kernel.org/linux-mm/20210516144152.GA25903@xsang-OptiPlex-9020/

Reported-and-tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 mm/slub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index 6b896b8c36f0..04824dae2e32 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -623,7 +623,7 @@ static void set_track(struct kmem_cache *s, void *object,
 
 	if (addr) {
 #ifdef CONFIG_STACKDEPOT
-		p->handle = save_stack_depot_trace(GFP_KERNEL);
+		p->handle = save_stack_depot_trace(GFP_NOWAIT);
 #endif
 		p->addr = addr;
 		p->cpu = smp_processor_id();
-- 
2.31.1