Hi:

After upgrade to kernel-6.6-y we face a panic on vma_merge()

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000078
Mem abort info:
  ESR = 0x0000000096000006
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x06: level 2 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
user pgtable: 4k pages, 39-bit VAs, pgdp=0000000a381d0000
[0000000000000078] pgd=0800000a381d1003, p4d=0800000a381d1003, pud=0800000a381d1003, pmd=0000000000000000
Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
Skip md ftrace buffer dump for: 0x1609e0
CPU: 7 PID: 11563 Comm: x Tainted: G        W  OE      6.6.56-android15
Hardware name: Qualcomm Technologies, Inc. Parrot QRD, Alpha-M (DT)
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : mab_mas_cp+0xb0/0x278
lr : mas_spanning_rebalance+0x830/0xeb4
sp : ffffffc0b2323410
x29: ffffffc0b2323420 x28: 0000000000000009 x27: 0000000000000001
x26: ffffff804c0ddb0c x25: 0000000000000001 x24: 0000000000000008
x23: 000000000000000c x22: 000000000000000c x21: ffffffc0b23236d0
x20: 0000000000000000 x19: ffffffc0b2323690 x18: ffffffc0ac5a2088
x17: 0000000000000000 x16: ffffff89b7d68d48 x15: ffffff897cfb6898
x14: ffffff89ca568000 x13: ffffff88082e74b0 x12: 0000000000000000
x11: 000000000000000f x10: 0000000000000080 x9 : 000000000000000d
x8 : 000000000000000d x7 : ffffff89d16690c8 x6 : ffffff87b3847bb8
x5 : ffffff804c0ddbe8 x4 : 0000000000000000 x3 : ffffffc0b23234c8
x2 : 0000000000000019 x1 : 000000000000000d x0 : 0000000000000080
Call trace:
 mab_mas_cp+0xb0/0x278
 mas_spanning_rebalance+0x830/0xeb4
 mas_wr_spanning_store+0x8ac/0xa58
 mas_wr_store_entry+0x130/0x180
 mas_store_prealloc+0x98/0x1bc
 vma_iter_store+0x64/0x74
 vma_merge+0x5e4/0x73c
 mmap_region+0x8d8/0xa30
 do_mmap+0x3e0/0x578
 vm_mmap_pgoff+0x1a0/0x1f8
 ksys_mmap_pgoff+0x78/0xf4
 __arm64_sys_mmap+0x34/0x44
 invoke_syscall+0x58/0x114
 el0_svc_common+0x80/0xe0
 do_el0_svc+0x1c/0x28
 el0_svc+0x38/0x68
 el0t_64_sync_handler+0x68/0xbc
 el0t_64_sync+0x1a8/0x1ac

the issue introduced by bdc136e2b05f ("mm: resolve faulty mmap_region() error path behaviour")

the reason is that call vma_iter_prealloc() twice and the maple_state is invalid. I write a reproducer here
by cat /proc/maple_test_merge the patch in attachment(maple_tree_debug.patch).

the reproducer simulates vma mmap at frist. then mmap_region() vma_merge(), 

the code from stable-6.6.y
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/tree/mm/mmap.c?h=linux-6.6.y

the reason show as follows
maple_tree
               parent
    leaf_1(..|c)   leaf_2(d..f|..)

__mmap_region(addr=d)
    1. vma_iter_prealloc()
        mas_state node=leaf_2 alloc=*mt_alloc_one* new_node_a

    2. mmap_file(file, vma)
        the vm_flags changed by some driver (ashmem) https://android.googlesource.com/kernel/msm/+/android-6.0.1_r0.74/drivers/staging/android/ashmem.c#312

vma_merge() (c can merge with d)
    3. vma_prev()
        mas_state node=leaf_1 alloc=new_node_a
    5. vma_iter_config()
        mas_state node=parent alloc=new_node_a
    4. vma_iter_prealloc()
        mas_state node=parent alloc=new_node_a
    6. vma_iter_store() --> panic
        use invalid new_node_a for spanning write


IMO, this issue can be fixed by mmap side maybe conflict with the patch. if
fix in maple_tree which need to destory the new_node_a


Brs,
Hailong.