mm/vmalloc: skip the uninitilized vmalloc areas

For areas allocated via vmalloc_xxx() APIs, it searches for unmapped area
to reserve and allocates new pages to map into, please see function
__vmalloc_node_range().  During the process, flag VM_UNINITIALIZED is set
in vm->flags to indicate that the pages allocation and mapping haven't
been done, until clear_vm_uninitialized_flag() is called to clear
VM_UNINITIALIZED.

For this kind of area, if VM_UNINITIALIZED is still set, let's ignore it
in vread() because pages newly allocated and being mapped in that area
only contains zero data.  reading them out by aligned_vread() is wasting
time.

Link: https://lkml.kernel.org/r/20230206084020.174506-6-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 87d71c783646b2c6d637f6edd97c04ca35cb20f8..3b57260b6d3927063f6d90860741b84a8bc21338 100644 (file)
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3587,6 +3587,11 @@ long vread(char *buf, char *addr, unsigned long count)
                if (!vm && !flags)
                        continue;
 
+               if (vm && (vm->flags & VM_UNINITIALIZED))
+                       continue;
+               /* Pair with smp_wmb() in clear_vm_uninitialized_flag() */
+               smp_rmb();
+
                vaddr = (char *) va->va_start;
                size = vm ? get_vm_area_size(vm) : va_size(va);