bcachefs: Reuse transaction

bcachefs: Reuse transaction

bch2_nocow_write_convert_unwritten is already in transaction context:

00191 ========= TEST   generic/648
00242 kernel BUG at fs/bcachefs/btree_iter.c:3332!
00242 Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
00242 Modules linked in:
00242 CPU: 4 UID: 0 PID: 2593 Comm: fsstress Not tainted 6.13.0-rc3-ktest-g345af8f855b7 #14403
00242 Hardware name: linux,dummy-virt (DT)
00242 pstate: 60001005 (nZCv daif -PAN -UAO -TCO -DIT +SSBS BTYPE=--)
00242 pc : __bch2_trans_get+0x120/0x410
00242 lr : __bch2_trans_get+0xcc/0x410
00242 sp : ffffff80d89af600
00242 x29: ffffff80d89af600 x28: ffffff80ddb23000 x27: 00000000fffff705
00242 x26: ffffff80ddb23028 x25: ffffff80d8903fe0 x24: ffffff80ebb30168
00242 x23: ffffff80c8aeb500 x22: 000000000000005d x21: ffffff80d8904078
00242 x20: ffffff80d8900000 x19: ffffff80da9e8000 x18: 0000000000000000
00242 x17: 64747568735f6c61 x16: 6e72756f6a20726f x15: 0000000000000028
00242 x14: 0000000000000004 x13: 000000000000f787 x12: ffffffc081bbcdc8
00242 x11: 0000000000000000 x10: 0000000000000003 x9 : ffffffc08094efbc
00242 x8 : 000000001092c111 x7 : 000000000000000c x6 : ffffffc083c31fc4
00242 x5 : ffffffc083c31f28 x4 : ffffff80c8aeb500 x3 : ffffff80ebb30000
00242 x2 : 0000000000000001 x1 : 0000000000000a21 x0 : 000000000000028e
00242 Call trace:
00242  __bch2_trans_get+0x120/0x410 (P)
00242  bch2_inum_offset_err_msg+0x48/0xb0
00242  bch2_nocow_write_convert_unwritten+0x3d0/0x530
00242  bch2_nocow_write+0xeb0/0x1000
00242  __bch2_write+0x330/0x4e8
00242  bch2_write+0x1f0/0x530
00242  bch2_direct_write+0x530/0xc00
00242  bch2_write_iter+0x160/0xbe0
00242  vfs_write+0x1cc/0x360
00242  ksys_write+0x5c/0xf0
00242  __arm64_sys_write+0x20/0x30
00242  invoke_syscall.constprop.0+0x54/0xe8
00242  do_el0_svc+0x44/0xc0
00242  el0_svc+0x34/0xa0
00242  el0t_64_sync_handler+0x104/0x130
00242  el0t_64_sync+0x154/0x158
00242 Code: 6b01001f 54ffff01 79408460 3617fec0 (d4210000)
00242 ---[ end trace 0000000000000000 ]---
00242 Kernel panic - not syncing: Oops - BUG: Fatal exception

Signed-off-by: Alan Huang <mmpgouride@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>