Hi Joe Zdenek recently got a lockdep warning in dm-thin. See this: http://pastebin.test.redhat.com/65346 I looked at the warning and realized that it is not a false alarm, but a real bug. Lockdep warns about dependency &md->io_lock -> &md->map_lock, but io_lock is a semaphore and map_lock is a spinlock, so such lock ordering should be always allowed (you can't take them in reverse order, because you can't take a semaphore while holding a spinlock). Looking deeper in the warning, it complains that there is an exeisting dependency chain &md->map_lock --> &pmd->root_lock --> &md->io_lock Here, map_lock is a spinlock and root_lock is a semaphore, this order of taking locks is obviously wrong. Cutting relevant part of the backtrace, we see: 41. [ 3836.656384] -> #1 (&pmd->root_lock){+++++.}: 42. [ 3836.656384] [<ffffffff81090740>] lock_acquire+0x90/0x1f0 43. [ 3836.656384] [<ffffffff814ac1ce>] down_read+0x3e/0x86 44. [ 3836.656384] [<ffffffffa02aaafe>] dm_pool_get_data_dev_size+0x2e/0x60 [dm_thin_pool] 45. [ 3836.656384] [<ffffffffa02a615b>] thin_iterate_devices+0x3b/0x80 [dm_thin_pool] 46. [ 3836.656384] [<ffffffffa006b2bf>] dm_table_supports_flush+0x5f/0x90 [dm_mod] 47. [ 3836.656384] [<ffffffffa006d2ec>] dm_table_set_restrictions+0x9c/0x180 [dm_mod] 48. [ 3836.656384] [<ffffffffa006a88a>] dm_swap_table+0x1da/0x2e0 [dm_mod] 49. [ 3836.656384] [<ffffffffa00701db>] dev_suspend+0x11b/0x260 [dm_mod] 50. [ 3836.656384] [<ffffffffa007089a>] ctl_ioctl+0x15a/0x2c0 [dm_mod] dm_swap_table calls __bind (which is not shown because it is inlined), __bind takes a spinlock &md->map_lock and calls dm_table_set_restrictions, from there, the code goes to thin_iterate_devices and it tries to take a semaphore &pmd->root_lock. So there is a clear bug, dm-thin is taking a semaphore while spinlock &md->map_lock is held. Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
