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/[email protected]
Signed-off-by: Baoquan He <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Reviewed-by: Uladzislau Rezki (Sony) <[email protected]>
Cc: Dan Carpenter <[email protected]>
Cc: Stephen Brennan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 5 insertions, 0 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 87d71c783646..3b57260b6d39 100644
--- 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);