mm/codetag: fix null pointer check logic for ref and tag

mm/codetag: fix null pointer check logic for ref and tag

When we compile and load lib/slub_kunit.c,it will cause a panic.

The root cause is that __kmalloc_cache_noprof was directly called instead
of kmem_cache_alloc,which resulted in no alloc_tag being allocated.This
caused current->alloc_tag to be null,leading to a null pointer dereference
in alloc_tag_ref_set.

Despite the fact that my colleague Pei Xiao will later fix the code in
slub_kunit.c,we still need fix null pointer check logic for ref and tag to
avoid panic caused by a null pointer dereference.

Here is the log for the panic:

[   74.779373][ T2158] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
[   74.780130][ T2158] Mem abort info:
[   74.780406][ T2158]   ESR = 0x0000000096000004
[   74.780756][ T2158]   EC = 0x25: DABT (current EL), IL = 32 bits
[   74.781225][ T2158]   SET = 0, FnV = 0
[   74.781529][ T2158]   EA = 0, S1PTW = 0
[   74.781836][ T2158]   FSC = 0x04: level 0 translation fault
[   74.782288][ T2158] Data abort info:
[   74.782577][ T2158]   ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
[   74.783068][ T2158]   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[   74.783533][ T2158]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[   74.784010][ T2158] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000105f34000
[   74.784586][ T2158] [0000000000000020] pgd=0000000000000000, p4d=0000000000000000
[   74.785293][ T2158] Internal error: Oops: 0000000096000004 [#1] SMP
[   74.785805][ T2158] Modules linked in: slub_kunit kunit ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ebtable_broute ip6table_nat ip6table_mangle 4
[   74.790661][ T2158] CPU: 0 UID: 0 PID: 2158 Comm: kunit_try_catch Kdump: loaded Tainted: G        W        N 6.12.0-rc3+ #2
[   74.791535][ T2158] Tainted: [W]=WARN, [N]=TEST
[   74.791889][ T2158] Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
[   74.792479][ T2158] pstate: 40400005 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   74.793101][ T2158] pc : alloc_tagging_slab_alloc_hook+0x120/0x270
[   74.793607][ T2158] lr : alloc_tagging_slab_alloc_hook+0x120/0x270
[   74.794095][ T2158] sp : ffff800084d33cd0
[   74.794418][ T2158] x29: ffff800084d33cd0 x28: 0000000000000000 x27: 0000000000000000
[   74.795095][ T2158] x26: 0000000000000000 x25: 0000000000000012 x24: ffff80007b30e314
[   74.795822][ T2158] x23: ffff000390ff6f10 x22: 0000000000000000 x21: 0000000000000088
[   74.796555][ T2158] x20: ffff000390285840 x19: fffffd7fc3ef7830 x18: ffffffffffffffff
[   74.797283][ T2158] x17: ffff8000800e63b4 x16: ffff80007b33afc4 x15: ffff800081654c00
[   74.798011][ T2158] x14: 0000000000000000 x13: 205d383531325420 x12: 5b5d383734363537
[   74.798744][ T2158] x11: ffff800084d337e0 x10: 000000000000005d x9 : 00000000ffffffd0
[   74.799476][ T2158] x8 : 7f7f7f7f7f7f7f7f x7 : ffff80008219d188 x6 : c0000000ffff7fff
[   74.800206][ T2158] x5 : ffff0003fdbc9208 x4 : ffff800081edd188 x3 : 0000000000000001
[   74.800932][ T2158] x2 : 0beaa6dee1ac5a00 x1 : 0beaa6dee1ac5a00 x0 : ffff80037c2cb000
[   74.801656][ T2158] Call trace:
[   74.801954][ T2158]  alloc_tagging_slab_alloc_hook+0x120/0x270
[   74.802494][ T2158]  __kmalloc_cache_noprof+0x148/0x33c
[   74.802976][ T2158]  test_kmalloc_redzone_access+0x4c/0x104 [slub_kunit]
[   74.803607][ T2158]  kunit_try_run_case+0x70/0x17c [kunit]
[   74.804124][ T2158]  kunit_generic_run_threadfn_adapter+0x2c/0x4c [kunit]
[   74.804768][ T2158]  kthread+0x10c/0x118
[   74.805141][ T2158]  ret_from_fork+0x10/0x20
[   74.805540][ T2158] Code: b9400a80 11000400 b9000a80 97ffd858 (f94012d3)
[   74.806176][ T2158] SMP: stopping secondary CPUs
[   74.808130][ T2158] Starting crashdump kernel...

Link: https://lkml.kernel.org/r/20241020070819.307944-1-hao.ge@linux.dev
Fixes: e0a955bf7f61 ("mm/codetag: add pgalloc_tag_copy()")
Signed-off-by: Hao Ge <gehao@kylinos.cn>
Acked-by: Suren Baghdasaryan <surenb@google.com>
Suggested-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Yu Zhao <yuzhao@google.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>