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  5. 05 Jun, 2019 1 commit
    • Yan, Zheng's avatar
      ceph: avoid iput_final() while holding mutex or in dispatch thread · 3e1d0452
      Yan, Zheng authored
      iput_final() may wait for reahahead pages. The wait can cause deadlock.
      For example:
      
        Workqueue: ceph-msgr ceph_con_workfn [libceph]
          Call Trace:
           schedule+0x36/0x80
           io_schedule+0x16/0x40
           __lock_page+0x101/0x140
           truncate_inode_pages_range+0x556/0x9f0
           truncate_inode_pages_final+0x4d/0x60
           evict+0x182/0x1a0
           iput+0x1d2/0x220
           iterate_session_caps+0x82/0x230 [ceph]
           dispatch+0x678/0xa80 [ceph]
           ceph_con_workfn+0x95b/0x1560 [libceph]
           process_one_work+0x14d/0x410
           worker_thread+0x4b/0x460
           kthread+0x105/0x140
           ret_from_fork+0x22/0x40
      
        Workqueue: ceph-msgr ceph_con_workfn [libceph]
          Call Trace:
           __schedule+0x3d6/0x8b0
           schedule+0x36/0x80
           schedule_preempt_disabled+0xe/0x10
           mutex_lock+0x2f/0x40
           ceph_check_caps+0x505/0xa80 [ceph]
           ceph_put_wrbuffer_cap_refs+0x1e5/0x2c0 [ceph]
           writepages_finish+0x2d3/0x410 [ceph]
           __complete_request+0x26/0x60 [libceph]
           handle_reply+0x6c8/0xa10 [libceph]
           dispatch+0x29a/0xbb0 [libceph]
           ceph_con_workfn+0x95b/0x1560 [libceph]
           process_one_work+0x14d/0x410
           worker_thread+0x4b/0x460
           kthread+0x105/0x140
           ret_from_fork+0x22/0x40
      
      In above example, truncate_inode_pages_range() waits for readahead pages
      while holding s_mutex. ceph_check_caps() waits for s_mutex and blocks
      OSD dispatch thread. Later OSD replies (for readahead) can't be handled.
      
      ceph_check_caps() also may lock snap_rwsem for read. So similar deadlock
      can happen if iput_final() is called while holding snap_rwsem.
      
      In general, it's not good to call iput_final() inside MDS/OSD dispatch
      threads or while holding any mutex.
      
      The fix is introducing ceph_async_iput(), which calls iput_final() in
      workqueue.
      Signed-off-by: default avatar"Yan, Zheng" <zyan@redhat.com>
      Reviewed-by: default avatarJeff Layton <jlayton@redhat.com>
      Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
      3e1d0452
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  10. 08 Nov, 2018 1 commit