Re: scheduling while atomic in z3fold

[Vitaly Wool <vitaly.wool@konsulko.com>]

On Thu, Dec 3, 2020 at 2:39 PM Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
>
> On 2020-12-03 09:18:21 [+0100], Mike Galbraith wrote:
> > On Thu, 2020-12-03 at 03:16 +0100, Mike Galbraith wrote:
> > > On Wed, 2020-12-02 at 23:08 +0100, Sebastian Andrzej Siewior wrote:
> > > Looks like...
> > >
> > > d8f117abb380 z3fold: fix use-after-free when freeing handles
> > >
> > > ...wasn't completely effective...
> >
> > The top two hunks seem to have rendered the thing RT tolerant.

Thanks for all your efforts, I promise to take a closer look at this
today, has had my hands full with RISC-V up until now.

Best regards,
   Vitaly

> Yes, it appears to. I have no idea if this is a proper fix or not.
> Without your write lock, after a few attempts, KASAN says:
>
> | BUG: KASAN: use-after-free in __pv_queued_spin_lock_slowpath+0x293/0x770
> | Write of size 2 at addr ffff88800e0e10aa by task kworker/u16:3/237
> |
> | CPU: 5 PID: 237 Comm: kworker/u16:3 Tainted: G        W         5.10.0-rc6-rt13-rt+
> | Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-1 04/01/2014
> | Workqueue: zswap1 compact_page_work
> | Call Trace:
> |  dump_stack+0x7d/0xa3
> |  print_address_description.constprop.0+0x19/0x120
> |  __kasan_report.cold+0x1d/0x35
> |  kasan_report+0x3a/0x50
> |  check_memory_region+0x145/0x1a0
> |  __pv_queued_spin_lock_slowpath+0x293/0x770
> |  _raw_spin_lock_irq+0xca/0xe0
> |  rt_read_unlock+0x2c/0x70
> |  __release_z3fold_page.constprop.0+0x45e/0x620
> |  do_compact_page+0x674/0xa50
> |  process_one_work+0x63a/0x1130
> |  worker_thread+0xd3/0xc80
> |  kthread+0x401/0x4e0
> |  ret_from_fork+0x22/0x30
> |
> | Allocated by task 225 (systemd-journal):
> |  kasan_save_stack+0x1b/0x40
> |  __kasan_kmalloc.constprop.0+0xc2/0xd0
> |  kmem_cache_alloc+0x103/0x2b0
> |  z3fold_alloc+0x597/0x1970
> |  zswap_frontswap_store+0x928/0x1bf0
> |  __frontswap_store+0x117/0x320
> |  swap_writepage+0x34/0x70
> |  pageout+0x268/0x7c0
> |  shrink_page_list+0x13e1/0x1e80
> |  shrink_inactive_list+0x303/0xde0
> |  shrink_lruvec+0x3dd/0x660
> |  shrink_node_memcgs+0x3a1/0x600
> |  shrink_node+0x3a7/0x1350
> |  shrink_zones+0x1f1/0x7f0
> |  do_try_to_free_pages+0x219/0xcc0
> |  try_to_free_pages+0x1c5/0x4b0
> |  __perform_reclaim+0x18f/0x2c0
> |  __alloc_pages_slowpath.constprop.0+0x7ea/0x1790
> |  __alloc_pages_nodemask+0x5f5/0x700
> |  page_cache_ra_unbounded+0x30f/0x690
> |  do_sync_mmap_readahead+0x3e3/0x640
> |  filemap_fault+0x981/0x1110
> |  __xfs_filemap_fault+0x12d/0x840
> |  __do_fault+0xf3/0x4b0
> |  do_fault+0x202/0x8c0
> |  __handle_mm_fault+0x338/0x500
> |  handle_mm_fault+0x1a8/0x670
> |  do_user_addr_fault+0x409/0x8b0
> |  exc_page_fault+0x60/0xc0
> |  asm_exc_page_fault+0x1e/0x30
> |
> | Freed by task 71 (oom_reaper):
> |  kasan_save_stack+0x1b/0x40
> |  kasan_set_track+0x1c/0x30
> |  kasan_set_free_info+0x1b/0x30
> |  __kasan_slab_free+0x110/0x150
> |  kmem_cache_free+0x7f/0x450
> |  z3fold_free+0x1f8/0xc90
> |  zswap_free_entry+0x168/0x230
> |  zswap_frontswap_invalidate_page+0x145/0x190
> |  __frontswap_invalidate_page+0xe8/0x1a0
> |  swap_range_free.constprop.0+0x266/0x300
> |  swapcache_free_entries+0x1dc/0x970
> |  free_swap_slot+0x19c/0x290
> |  __swap_entry_free+0x139/0x160
> |  free_swap_and_cache+0xda/0x230
> |  zap_pte_range+0x275/0x1590
> |  unmap_page_range+0x320/0x690
> |  __oom_reap_task_mm+0x207/0x330
> |  oom_reap_task_mm+0x78/0x7e0
> |  oom_reap_task+0x6d/0x1a0
> |  oom_reaper+0x103/0x290
> |  kthread+0x401/0x4e0
> |  ret_from_fork+0x22/0x30
> |
> | The buggy address belongs to the object at ffff88800e0e1080
> |  which belongs to the cache z3fold_handle of size 88
> | The buggy address is located 42 bytes inside of
> |  88-byte region [ffff88800e0e1080, ffff88800e0e10d8)
> | The buggy address belongs to the page:
> | page:000000002ba661bc refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xe0e1
> | flags: 0xffff800000200(slab)
> | raw: 000ffff800000200 dead000000000100 dead000000000122 ffff88800aa4eb40
> | raw: 0000000000000000 0000000000200020 00000001ffffffff 0000000000000000
> | page dumped because: kasan: bad access detected
> |
> | Memory state around the buggy address:
> |  ffff88800e0e0f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> |  ffff88800e0e1000: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
> | >ffff88800e0e1080: fa fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc
> |                                   ^
> |  ffff88800e0e1100: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
> |  ffff88800e0e1180: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
> | ==================================================================
> | Disabling lock debugging due to kernel taint
>
> with the lock I haven't seen anything.
>
> Sebastian