btrfs: fix use-after-free in btrfs_encoded_read_endio()
In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix use-after-free in btrfs_encoded_read_endio()

Shinichiro reported the following use-after free that sometimes is
happening in our CI system when running fstests' btrfs/284 on a TCMU
runner device:

  BUG: KASAN: slab-use-after-free in lock_release+0x708/0x780
  Read of size 8 at addr ffff888106a83f18 by task kworker/u80:6/219

  CPU: 8 UID: 0 PID: 219 Comm: kworker/u80:6 Not tainted 6.12.0-rc6-kts+ #15
  Hardware name: Supermicro Super Server/X11SPi-TF, BIOS 3.3 02/21/2020
  Workqueue: btrfs-endio btrfs_end_bio_work [btrfs]
  Call Trace:
   <TASK>
   dump_stack_lvl+0x6e/0xa0
   ? lock_release+0x708/0x780
   print_report+0x174/0x505
   ? lock_release+0x708/0x780
   ? __virt_addr_valid+0x224/0x410
   ? lock_release+0x708/0x780
   kasan_report+0xda/0x1b0
   ? lock_release+0x708/0x780
   ? __wake_up+0x44/0x60
   lock_release+0x708/0x780
   ? __pfx_lock_release+0x10/0x10
   ? __pfx_do_raw_spin_lock+0x10/0x10
   ? lock_is_held_type+0x9a/0x110
   _raw_spin_unlock_irqrestore+0x1f/0x60
   __wake_up+0x44/0x60
   btrfs_encoded_read_endio+0x14b/0x190 [btrfs]
   btrfs_check_read_bio+0x8d9/0x1360 [btrfs]
   ? lock_release+0x1b0/0x780
   ? trace_lock_acquire+0x12f/0x1a0
   ? __pfx_btrfs_check_read_bio+0x10/0x10 [btrfs]
   ? process_one_work+0x7e3/0x1460
   ? lock_acquire+0x31/0xc0
   ? process_one_work+0x7e3/0x1460
   process_one_work+0x85c/0x1460
   ? __pfx_process_one_work+0x10/0x10
   ? assign_work+0x16c/0x240
   worker_thread+0x5e6/0xfc0
   ? __pfx_worker_thread+0x10/0x10
   kthread+0x2c3/0x3a0
   ? __pfx_kthread+0x10/0x10
   ret_from_fork+0x31/0x70
   ? __pfx_kthread+0x10/0x10
   ret_from_fork_asm+0x1a/0x30
   </TASK>

  Allocated by task 3661:
   kasan_save_stack+0x30/0x50
   kasan_save_track+0x14/0x30
   __kasan_kmalloc+0xaa/0xb0
   btrfs_encoded_read_regular_fill_pages+0x16c/0x6d0 [btrfs]
   send_extent_data+0xf0f/0x24a0 [btrfs]
   process_extent+0x48a/0x1830 [btrfs]
   changed_cb+0x178b/0x2ea0 [btrfs]
   btrfs_ioctl_send+0x3bf9/0x5c20 [btrfs]
   _btrfs_ioctl_send+0x117/0x330 [btrfs]
   btrfs_ioctl+0x184a/0x60a0 [btrfs]
   __x64_sys_ioctl+0x12e/0x1a0
   do_syscall_64+0x95/0x180
   entry_SYSCALL_64_after_hwframe+0x76/0x7e

  Freed by task 3661:
   kasan_save_stack+0x30/0x50
   kasan_save_track+0x14/0x30
   kasan_save_free_info+0x3b/0x70
   __kasan_slab_free+0x4f/0x70
   kfree+0x143/0x490
   btrfs_encoded_read_regular_fill_pages+0x531/0x6d0 [btrfs]
   send_extent_data+0xf0f/0x24a0 [btrfs]
   process_extent+0x48a/0x1830 [btrfs]
   changed_cb+0x178b/0x2ea0 [btrfs]
   btrfs_ioctl_send+0x3bf9/0x5c20 [btrfs]
   _btrfs_ioctl_send+0x117/0x330 [btrfs]
   btrfs_ioctl+0x184a/0x60a0 [btrfs]
   __x64_sys_ioctl+0x12e/0x1a0
   do_syscall_64+0x95/0x180
   entry_SYSCALL_64_after_hwframe+0x76/0x7e

  The buggy address belongs to the object at ffff888106a83f00
   which belongs to the cache kmalloc-rnd-07-96 of size 96
  The buggy address is located 24 bytes inside of
   freed 96-byte region [ffff888106a83f00, ffff888106a83f60)

  The buggy address belongs to the physical page:
  page: refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888106a83800 pfn:0x106a83
  flags: 0x17ffffc0000000(node=0|zone=2|lastcpupid=0x1fffff)
  page_type: f5(slab)
  raw: 0017ffffc0000000 ffff888100053680 ffffea0004917200 0000000000000004
  raw: ffff888106a83800 0000000080200019 00000001f5000000 0000000000000000
  page dumped because: kasan: bad access detected

  Memory state around the buggy address:
   ffff888106a83e00: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
   ffff888106a83e80: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
  >ffff888106a83f00: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
                              ^
   ffff888106a83f80: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
   ffff888106a84000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ==================================================================

Further analyzing the trace and 
---truncated---