On Wed, Dec 20, 2017 at 08:50:40AM +0100, Dmitry Vyukov wrote: > > > > The line number in lib/rbtree.c seems to be slightly off. Looking at the > > disassembly: > > > > ffffffff825b5ea0 <rb_insert_color>: > > ffffffff825b5ea0: 55 push %rbp > > ffffffff825b5ea1: 48 8b 17 mov (%rdi),%rdx > > ffffffff825b5ea4: 48 89 e5 mov %rsp,%rbp > > ffffffff825b5ea7: 48 85 d2 test %rdx,%rdx > > ffffffff825b5eaa: 0f 84 4c 01 00 00 je ffffffff825b5ffc <rb_insert_color+0x15c> > > ffffffff825b5eb0: 48 8b 02 mov (%rdx),%rax > > ffffffff825b5eb3: a8 01 test $0x1,%al > > ffffffff825b5eb5: 75 5e jne ffffffff825b5f15 <rb_insert_color+0x75> > > ffffffff825b5eb7: 48 8b 48 08 mov 0x8(%rax),%rcx > > > > It crashed on 'mov 0x8(%rax),%rcx' which corresponds to > > 'tmp = gparent->rb_right;' at lib/rbtree.c:131. So 'parent' was the root node, > > but its color was red, while it is supposed to be black. > > > > No idea how that happened, but it's almost certainly not an ext4 bug. In fact > > there is another report of this same crash that has a different call trace: > > > > Call Trace: > > key_alloc_serial security/keys/key.c:170 [inline] > > key_alloc+0x54c/0x5b0 security/keys/key.c:319 > > keyring_alloc+0x4d/0xb0 security/keys/keyring.c:503 > > install_process_keyring_to_cred.part.3+0x38/0x80 security/keys/process_keys.c:192 > > install_process_keyring_to_cred security/keys/process_keys.c:634 [inline] > > install_process_keyring security/keys/process_keys.c:217 [inline] > > lookup_user_key+0x4ed/0x7c0 security/keys/process_keys.c:574 > > SYSC_add_key security/keys/keyctl.c:114 [inline] > > SyS_add_key+0xec/0x260 security/keys/keyctl.c:62 > > entry_SYSCALL_64_fastpath+0x1f/0x96 > > > My first hypothesis for an non-explainable, non-reproducible > corruption would be a data race. Is there all locking in place? It doesn't seem to be a locking problem. In the ext4 case the rbtree is associated with a struct file's dir_private_info, which is protected by ->f_pos_lock (taken early in sys_getdents()). And in the keyrings case, the rbtree is protected by key_serial_lock. Eric
