stackdepot: use gfp_nested_mask() instead of open coded masking

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.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Dave Chinner <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Vlastimil Babka <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 2 insertions, 9 deletions

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index cd8f23455285..5ed34cc963fc 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, I/O, nolockdep.
-		 */
-		alloc_flags &= ~GFP_ZONEMASK;
-		alloc_flags &= (GFP_ATOMIC | GFP_KERNEL | __GFP_NOLOCKDEP);
-		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);
 	}