[PATCH 2/3] stackdepot: use gfp_nested_mask() instead of open coded masking

[Dave Chinner <david@fromorbit.com>]

From: Dave Chinner <dchinner@redhat.com>

The stackdepot code is used by KASAN and lockdep for recoding stack
traces. Both of these track allocation context information, and so
their internal allocations must obey the caller allocation contexts
to avoid generating their own false positive warnings that have
nothing to do with the code they are instrumenting/tracking.

We also don't want recording stack traces to deplete emergency
memory reserves - debug code is useless if it creates new issues
that can't be replicated when the debug code is disabled.

Switch the stackdepot allocation masking to use gfp_nested_mask()
to address these issues. gfp_nested_mask() also strips GFP_ZONEMASK
naturally, so that greatly simplifies this code.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 lib/stackdepot.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 68c97387aa54..0bbae49e6177 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -624,15 +624,8 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
 	 * we won't be able to do that under the lock.
 	 */
 	if (unlikely(can_alloc && !READ_ONCE(new_pool))) {
-		/*
-		 * Zero out zone modifiers, as we don't have specific zone
-		 * requirements. Keep the flags related to allocation in atomic
-		 * contexts and I/O.
-		 */
-		alloc_flags &= ~GFP_ZONEMASK;
-		alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
-		alloc_flags |= __GFP_NOWARN;
-		page = alloc_pages(alloc_flags, DEPOT_POOL_ORDER);
+		page = alloc_pages(gfp_nested_mask(alloc_flags),
+				DEPOT_POOL_ORDER);
 		if (page)
 			prealloc = page_address(page);
 	}
-- 
2.43.0