• Mikulas Patocka's avatar
    slub: fix failure when we delete and create a slab cache · d50d82fa
    Mikulas Patocka authored
    In kernel 4.17 I removed some code from dm-bufio that did slab cache
    merging (commit 21bb1327: "dm bufio: remove code that merges slab
    caches") - both slab and slub support merging caches with identical
    attributes, so dm-bufio now just calls kmem_cache_create and relies on
    implicit merging.
    
    This uncovered a bug in the slub subsystem - if we delete a cache and
    immediatelly create another cache with the same attributes, it fails
    because of duplicate filename in /sys/kernel/slab/.  The slub subsystem
    offloads freeing the cache to a workqueue - and if we create the new
    cache before the workqueue runs, it complains because of duplicate
    filename in sysfs.
    
    This patch fixes the bug by moving the call of kobject_del from
    sysfs_slab_remove_workfn to shutdown_cache.  kobject_del must be called
    while we hold slab_mutex - so that the sysfs entry is deleted before a
    cache with the same attributes could be created.
    
    Running device-mapper-test-suite with:
    
      dmtest run --suite thin-provisioning -n /commit_failure_causes_fallback/
    
    triggered:
    
      Buffer I/O error on dev dm-0, logical block 1572848, async page read
      device-mapper: thin: 253:1: metadata operation 'dm_pool_alloc_data_block' failed: error = -5
      device-mapper: thin: 253:1: aborting current metadata transaction
      sysfs: cannot create duplicate filename '/kernel/slab/:a-0000144'
      CPU: 2 PID: 1037 Comm: kworker/u48:1 Not tainted 4.17.0.snitm+ #25
      Hardware name: Supermicro SYS-1029P-WTR/X11DDW-L, BIOS 2.0a 12/06/2017
      Workqueue: dm-thin do_worker [dm_thin_pool]
      Call Trace:
       dump_stack+0x5a/0x73
       sysfs_warn_dup+0x58/0x70
       sysfs_create_dir_ns+0x77/0x80
       kobject_add_internal+0xba/0x2e0
       kobject_init_and_add+0x70/0xb0
       sysfs_slab_add+0xb1/0x250
       __kmem_cache_create+0x116/0x150
       create_cache+0xd9/0x1f0
       kmem_cache_create_usercopy+0x1c1/0x250
       kmem_cache_create+0x18/0x20
       dm_bufio_client_create+0x1ae/0x410 [dm_bufio]
       dm_block_manager_create+0x5e/0x90 [dm_persistent_data]
       __create_persistent_data_objects+0x38/0x940 [dm_thin_pool]
       dm_pool_abort_metadata+0x64/0x90 [dm_thin_pool]
       metadata_operation_failed+0x59/0x100 [dm_thin_pool]
       alloc_data_block.isra.53+0x86/0x180 [dm_thin_pool]
       process_cell+0x2a3/0x550 [dm_thin_pool]
       do_worker+0x28d/0x8f0 [dm_thin_pool]
       process_one_work+0x171/0x370
       worker_thread+0x49/0x3f0
       kthread+0xf8/0x130
       ret_from_fork+0x35/0x40
      kobject_add_internal failed for :a-0000144 with -EEXIST, don't try to register things with the same name in the same directory.
      kmem_cache_create(dm_bufio_buffer-16) failed with error -17
    
    Link: http://lkml.kernel.org/r/alpine.LRH.2.02.1806151817130.6333@file01.intranet.prod.int.rdu2.redhat.comSigned-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
    Reported-by: default avatarMike Snitzer <snitzer@redhat.com>
    Tested-by: default avatarMike Snitzer <snitzer@redhat.com>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Pekka Enberg <penberg@kernel.org>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    d50d82fa