mm: skip might_alloc() warnings when PF_MEMALLOC is set

might_alloc() catches invalid blocking allocations in contexts where
sleeping is not allowed.

However when PF_MEMALLOC is set, the page allocator already skips reclaim
and other blocking paths.  In such cases, a blocking gfp_mask does not
actually lead to blocking, so triggering might_alloc() splats is
misleading.

Adjust might_alloc() to skip warnings when the current task has
PF_MEMALLOC set, matching the allocator's actual blocking behaviour.

Link: https://lkml.kernel.org/r/20251007122035.56347-9-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/sched/mm.h

@@ -318,6 +318,9 @@ static inline void might_alloc(gfp_t gfp_mask)
 	fs_reclaim_acquire(gfp_mask);
 	fs_reclaim_release(gfp_mask);
 
+	if (current->flags & PF_MEMALLOC)
+		return;
+
 	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
 }