• Rabin Vincent's avatar
    CIFS: fix oplock break deadlocks · 3998e6b8
    Rabin Vincent authored
    When the final cifsFileInfo_put() is called from cifsiod and an oplock
    break work is queued, lockdep complains loudly:
    
     =============================================
     [ INFO: possible recursive locking detected ]
     4.11.0+ #21 Not tainted
     ---------------------------------------------
     kworker/0:2/78 is trying to acquire lock:
      ("cifsiod"){++++.+}, at: flush_work+0x215/0x350
    
     but task is already holding lock:
      ("cifsiod"){++++.+}, at: process_one_work+0x255/0x8e0
    
     other info that might help us debug this:
      Possible unsafe locking scenario:
    
            CPU0
            ----
       lock("cifsiod");
       lock("cifsiod");
    
      *** DEADLOCK ***
    
      May be due to missing lock nesting notation
    
     2 locks held by kworker/0:2/78:
      #0:  ("cifsiod"){++++.+}, at: process_one_work+0x255/0x8e0
      #1:  ((&wdata->work)){+.+...}, at: process_one_work+0x255/0x8e0
    
     stack backtrace:
     CPU: 0 PID: 78 Comm: kworker/0:2 Not tainted 4.11.0+ #21
     Workqueue: cifsiod cifs_writev_complete
     Call Trace:
      dump_stack+0x85/0xc2
      __lock_acquire+0x17dd/0x2260
      ? match_held_lock+0x20/0x2b0
      ? trace_hardirqs_off_caller+0x86/0x130
      ? mark_lock+0xa6/0x920
      lock_acquire+0xcc/0x260
      ? lock_acquire+0xcc/0x260
      ? flush_work+0x215/0x350
      flush_work+0x236/0x350
      ? flush_work+0x215/0x350
      ? destroy_worker+0x170/0x170
      __cancel_work_timer+0x17d/0x210
      ? ___preempt_schedule+0x16/0x18
      cancel_work_sync+0x10/0x20
      cifsFileInfo_put+0x338/0x7f0
      cifs_writedata_release+0x2a/0x40
      ? cifs_writedata_release+0x2a/0x40
      cifs_writev_complete+0x29d/0x850
      ? preempt_count_sub+0x18/0xd0
      process_one_work+0x304/0x8e0
      worker_thread+0x9b/0x6a0
      kthread+0x1b2/0x200
      ? process_one_work+0x8e0/0x8e0
      ? kthread_create_on_node+0x40/0x40
      ret_from_fork+0x31/0x40
    
    This is a real warning.  Since the oplock is queued on the same
    workqueue this can deadlock if there is only one worker thread active
    for the workqueue (which will be the case during memory pressure when
    the rescuer thread is handling it).
    
    Furthermore, there is at least one other kind of hang possible due to
    the oplock break handling if there is only worker.  (This can be
    reproduced without introducing memory pressure by having passing 1 for
    the max_active parameter of cifsiod.) cifs_oplock_break() can wait
    indefintely in the filemap_fdatawait() while the cifs_writev_complete()
    work is blocked:
    
     sysrq: SysRq : Show Blocked State
       task                        PC stack   pid father
     kworker/0:1     D    0    16      2 0x00000000
     Workqueue: cifsiod cifs_oplock_break
     Call Trace:
      __schedule+0x562/0xf40
      ? mark_held_locks+0x4a/0xb0
      schedule+0x57/0xe0
      io_schedule+0x21/0x50
      wait_on_page_bit+0x143/0x190
      ? add_to_page_cache_lru+0x150/0x150
      __filemap_fdatawait_range+0x134/0x190
      ? do_writepages+0x51/0x70
      filemap_fdatawait_range+0x14/0x30
      filemap_fdatawait+0x3b/0x40
      cifs_oplock_break+0x651/0x710
      ? preempt_count_sub+0x18/0xd0
      process_one_work+0x304/0x8e0
      worker_thread+0x9b/0x6a0
      kthread+0x1b2/0x200
      ? process_one_work+0x8e0/0x8e0
      ? kthread_create_on_node+0x40/0x40
      ret_from_fork+0x31/0x40
     dd              D    0   683    171 0x00000000
     Call Trace:
      __schedule+0x562/0xf40
      ? mark_held_locks+0x29/0xb0
      schedule+0x57/0xe0
      io_schedule+0x21/0x50
      wait_on_page_bit+0x143/0x190
      ? add_to_page_cache_lru+0x150/0x150
      __filemap_fdatawait_range+0x134/0x190
      ? do_writepages+0x51/0x70
      filemap_fdatawait_range+0x14/0x30
      filemap_fdatawait+0x3b/0x40
      filemap_write_and_wait+0x4e/0x70
      cifs_flush+0x6a/0xb0
      filp_close+0x52/0xa0
      __close_fd+0xdc/0x150
      SyS_close+0x33/0x60
      entry_SYSCALL_64_fastpath+0x1f/0xbe
    
     Showing all locks held in the system:
     2 locks held by kworker/0:1/16:
      #0:  ("cifsiod"){.+.+.+}, at: process_one_work+0x255/0x8e0
      #1:  ((&cfile->oplock_break)){+.+.+.}, at: process_one_work+0x255/0x8e0
    
     Showing busy workqueues and worker pools:
     workqueue cifsiod: flags=0xc
       pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/1
         in-flight: 16:cifs_oplock_break
         delayed: cifs_writev_complete, cifs_echo_request
     pool 0: cpus=0 node=0 flags=0x0 nice=0 hung=0s workers=3 idle: 750 3
    
    Fix these problems by creating a a new workqueue (with a rescuer) for
    the oplock break work.
    Signed-off-by: default avatarRabin Vincent <rabinv@axis.com>
    Signed-off-by: default avatarSteve French <smfrench@gmail.com>
    CC: Stable <stable@vger.kernel.org>
    3998e6b8
smb2misc.c 20.3 KB