• Gui Jianfeng's avatar
    blk-cgroup: Fix potential deadlock in blk-cgroup · bcf4dd43
    Gui Jianfeng authored
    I triggered a lockdep warning as following.
    
    =======================================================
    [ INFO: possible circular locking dependency detected ]
    2.6.33-rc2 #1
    -------------------------------------------------------
    test_io_control/7357 is trying to acquire lock:
     (blkio_list_lock){+.+...}, at: [<c053a990>] blkiocg_weight_write+0x82/0x9e
    
    but task is already holding lock:
     (&(&blkcg->lock)->rlock){......}, at: [<c053a949>] blkiocg_weight_write+0x3b/0x9e
    
    which lock already depends on the new lock.
    
    the existing dependency chain (in reverse order) is:
    
    -> #2 (&(&blkcg->lock)->rlock){......}:
           [<c04583b7>] validate_chain+0x8bc/0xb9c
           [<c0458dba>] __lock_acquire+0x723/0x789
           [<c0458eb0>] lock_acquire+0x90/0xa7
           [<c0692b0a>] _raw_spin_lock_irqsave+0x27/0x5a
           [<c053a4e1>] blkiocg_add_blkio_group+0x1a/0x6d
           [<c053cac7>] cfq_get_queue+0x225/0x3de
           [<c053eec2>] cfq_set_request+0x217/0x42d
           [<c052c8a6>] elv_set_request+0x17/0x26
           [<c0532a0f>] get_request+0x203/0x2c5
           [<c0532ae9>] get_request_wait+0x18/0x10e
           [<c0533470>] __make_request+0x2ba/0x375
           [<c0531985>] generic_make_request+0x28d/0x30f
           [<c0532da7>] submit_bio+0x8a/0x8f
           [<c04d827a>] submit_bh+0xf0/0x10f
           [<c04d91d2>] ll_rw_block+0xc0/0xf9
           [<f86e9705>] ext3_find_entry+0x319/0x544 [ext3]
           [<f86eae58>] ext3_lookup+0x2c/0xb9 [ext3]
           [<c04c3e1b>] do_lookup+0xd3/0x172
           [<c04c56c8>] link_path_walk+0x5fb/0x95c
           [<c04c5a65>] path_walk+0x3c/0x81
           [<c04c5b63>] do_path_lookup+0x21/0x8a
           [<c04c66cc>] do_filp_open+0xf0/0x978
           [<c04c0c7e>] open_exec+0x1b/0xb7
           [<c04c1436>] do_execve+0xbb/0x266
           [<c04081a9>] sys_execve+0x24/0x4a
           [<c04028a2>] ptregs_execve+0x12/0x18
    
    -> #1 (&(&q->__queue_lock)->rlock){..-.-.}:
           [<c04583b7>] validate_chain+0x8bc/0xb9c
           [<c0458dba>] __lock_acquire+0x723/0x789
           [<c0458eb0>] lock_acquire+0x90/0xa7
           [<c0692b0a>] _raw_spin_lock_irqsave+0x27/0x5a
           [<c053dd2a>] cfq_unlink_blkio_group+0x17/0x41
           [<c053a6eb>] blkiocg_destroy+0x72/0xc7
           [<c0467df0>] cgroup_diput+0x4a/0xb2
           [<c04ca473>] dentry_iput+0x93/0xb7
           [<c04ca4b3>] d_kill+0x1c/0x36
           [<c04cb5c5>] dput+0xf5/0xfe
           [<c04c6084>] do_rmdir+0x95/0xbe
           [<c04c60ec>] sys_rmdir+0x10/0x12
           [<c04027cc>] sysenter_do_call+0x12/0x32
    
    -> #0 (blkio_list_lock){+.+...}:
           [<c0458117>] validate_chain+0x61c/0xb9c
           [<c0458dba>] __lock_acquire+0x723/0x789
           [<c0458eb0>] lock_acquire+0x90/0xa7
           [<c06929fd>] _raw_spin_lock+0x1e/0x4e
           [<c053a990>] blkiocg_weight_write+0x82/0x9e
           [<c0467f1e>] cgroup_file_write+0xc6/0x1c0
           [<c04bd2f3>] vfs_write+0x8c/0x116
           [<c04bd7c6>] sys_write+0x3b/0x60
           [<c04027cc>] sysenter_do_call+0x12/0x32
    
    other info that might help us debug this:
    
    1 lock held by test_io_control/7357:
     #0:  (&(&blkcg->lock)->rlock){......}, at: [<c053a949>] blkiocg_weight_write+0x3b/0x9e
    stack backtrace:
    Pid: 7357, comm: test_io_control Not tainted 2.6.33-rc2 #1
    Call Trace:
     [<c045754f>] print_circular_bug+0x91/0x9d
     [<c0458117>] validate_chain+0x61c/0xb9c
     [<c0458dba>] __lock_acquire+0x723/0x789
     [<c0458eb0>] lock_acquire+0x90/0xa7
     [<c053a990>] ? blkiocg_weight_write+0x82/0x9e
     [<c06929fd>] _raw_spin_lock+0x1e/0x4e
     [<c053a990>] ? blkiocg_weight_write+0x82/0x9e
     [<c053a990>] blkiocg_weight_write+0x82/0x9e
     [<c0467f1e>] cgroup_file_write+0xc6/0x1c0
     [<c0454df5>] ? trace_hardirqs_off+0xb/0xd
     [<c044d93a>] ? cpu_clock+0x2e/0x44
     [<c050e6ec>] ? security_file_permission+0xf/0x11
     [<c04bcdda>] ? rw_verify_area+0x8a/0xad
     [<c0467e58>] ? cgroup_file_write+0x0/0x1c0
     [<c04bd2f3>] vfs_write+0x8c/0x116
     [<c04bd7c6>] sys_write+0x3b/0x60
     [<c04027cc>] sysenter_do_call+0x12/0x32
    
    To prevent deadlock, we should take locks as following sequence:
    
    blkio_list_lock -> queue_lock ->  blkcg_lock.
    
    The following patch should fix this bug.
    Signed-off-by: default avatarGui Jianfeng <guijianfeng@cn.fujitsu.com>
    Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
    bcf4dd43
blk-cgroup.c 9.09 KB