Re: [PATCH] mm/kasan: Don't vfree() nonexistent vm_area.

[Andrey Ryabinin]

On 02/01/2018 07:33 PM, Andrey Ryabinin wrote:
> KASAN uses different routines to map shadow for hot added memory and memory
> obtained in boot process. Attempt to offline memory onlined by normal boot
> process leads to this:
> 
>     Trying to vfree() nonexistent vm area (000000005d3b34b9)
>     WARNING: CPU: 2 PID: 13215 at mm/vmalloc.c:1525 __vunmap+0x147/0x190
> 
>     Call Trace:
>      kasan_mem_notifier+0xad/0xb9
>      notifier_call_chain+0x166/0x260
>      __blocking_notifier_call_chain+0xdb/0x140
>      __offline_pages+0x96a/0xb10
>      memory_subsys_offline+0x76/0xc0
>      device_offline+0xb8/0x120
>      store_mem_state+0xfa/0x120
>      kernfs_fop_write+0x1d5/0x320
>      __vfs_write+0xd4/0x530
>      vfs_write+0x105/0x340
>      SyS_write+0xb0/0x140
> 
> Obviously we can't call vfree() to free memory that wasn't allocated via
> vmalloc(). Use find_vm_area() to see if we can call vfree().
> 
> Unfortunately it's a bit tricky to properly unmap and free shadow allocated
> during boot, so we'll have to keep it. If memory will come online again
> that shadow will be reused.
> 
> Fixes: fa69b5989bb0 ("mm/kasan: add support for memory hotplug")
> Reported-by: Paul Menzel <pmenzel+linux-kasan-dev@xxxxxxxxxxxxx>
> Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> ---

This seems stuck in -mm. Andrew, can we proceed?