Hello, Recently I started getting the following crashes on some servers, running btrfs:
[340435.480338] BTRFS info (device loop7): disk space caching is enabled [340435.480509] BTRFS: has skinny extents [340441.716174] BTRFS: checking UUID tree [340441.912070] BUG: unable to handle kernel NULL pointer dereference at 0000000000000098 [340441.912463] IP: [<ffffffffa081f774>] btrfs_uuid_tree_iterate+0xf4/0x2d0 [btrfs] [340441.912823] PGD 0 [340441.913035] Oops: 0000 [#1] SMP [340441.913302] Modules linked in: [340441.916996] CPU: 10 PID: 24990 Comm: btrfs-uuid Tainted: P W O 4.4.14-clouder1 #55 [340441.917287] Hardware name: Supermicro X9DRD-iF/LF/X9DRD-iF, BIOS 3.2 01/16/2015 [340441.917573] task: ffff8801b95c1b80 ti: ffff88034e504000 task.ti: ffff88034e504000 [340441.917859] RIP: 0010:[<ffffffffa081f774>] [<ffffffffa081f774>] btrfs_uuid_tree_iterate+0xf4/0x2d0 [btrfs] [340441.918212] RSP: 0018:ffff88034e507e20 EFLAGS: 00010246 [340441.918382] RAX: 0000000000000000 RBX: 0000160000000000 RCX: ffff880000000000 [340441.918665] RDX: 0000000000000001 RSI: ffff8801e3abd140 RDI: ffff88046f027f00 [340441.918952] RBP: ffff88034e507ea8 R08: 000060fb80001760 R09: ffffffffa07ac1de [340441.919236] R10: ffffe8ffffd41760 R11: ffffea00078eaf40 R12: ffff8801b98ab750 [340441.919521] R13: 00000000fffffffe R14: ffff8801e3abd140 R15: ffff880049586000 [340441.919810] FS: 0000000000000000(0000) GS:ffff88047fd40000(0000) knlGS:0000000000000000 [340441.920097] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [340441.920267] CR2: 0000000000000098 CR3: 0000000001c0a000 CR4: 00000000000406e0 [340441.920554] Stack: [340441.920717] ffff880049586000 ffff8801b98ab750 00003f7b00014fc0 ffff8803711dec08 [340441.921186] ffffffffa07d0c40 ffff880332342000 0000000000000114 1b7088046d7612f8 [340441.921655] 8cfb42689378e508 70157e0ade97f5d6 8c42689378e5081b 15157e0ade97f5d6 [340441.922126] Call Trace: [340441.922315] [<ffffffffa07d0c40>] ? find_live_mirror.isra.18+0xc0/0xc0 [btrfs] [340441.922614] [<ffffffffa07d0ae0>] ? btrfs_uuid_scan_kthread+0x3c0/0x3c0 [btrfs] [340441.922917] [<ffffffffa07d0afb>] btrfs_uuid_rescan_kthread+0x1b/0x60 [btrfs] [340441.923197] [<ffffffff8107161f>] kthread+0xef/0x110 [340441.923363] [<ffffffff81071530>] ? kthread_park+0x60/0x60 [340441.923531] [<ffffffff816149ff>] ret_from_fork+0x3f/0x70 [340441.923697] [<ffffffff81071530>] ? kthread_park+0x60/0x60 [340441.923863] Code: 0f 86 a0 00 00 00 48 bb 00 00 00 00 00 16 00 00 41 8b 44 24 40 48 b9 00 00 00 00 00 88 ff ff 8d 50 01 49 8b 04 24 41 89 54 24 40 <48> 03 98 98 00 00 00 48 89 d8 48 c1 f8 06 48 c1 e0 0c 3b 54 08 [340441.927296] RIP [<ffffffffa081f774>] btrfs_uuid_tree_iterate+0xf4/0x2d0 [btrfs] [340441.927641] RSP <ffff88034e507e20> [340441.927806] CR2: 0000000000000098 ffffffffa081f774 is in the heavily inlined btrfs_next_item. Here is the decoded instructions, right before the crash with annotations: 0: 0f 86 a0 00 00 00 jbe 0xa6 6: 48 bb 00 00 00 00 00 mov $0x160000000000,%rbx d: 16 00 00 10: 41 8b 44 24 40 mov 0x40(%r12),%eax ; r12 is btrfs_path, eax points to first slot 15: 48 b9 00 00 00 00 00 mov $0xffff880000000000,%rcx 1c: 88 ff ff 1f: 8d 50 01 lea 0x1(%rax),%edx ; incr slot 22: 49 8b 04 24 mov (%r12),%rax ; load first extent_buffer in rax 26: 41 89 54 24 40 mov %edx,0x40(%r12) ; save incremented slot 2b:* 48 03 98 98 00 00 00 add 0x98(%rax),%rbx <-- trapping instruction ; load the first page from the extent_buffer 32: 48 89 d8 mov %rbx,%rax 35: 48 c1 f8 06 sar $0x6,%rax 39: 48 c1 e0 0c shl $0xc,%rax 3d: 3b .byte 0x3b 3e: 54 push %rsp 3f: 08 .byte 0x8 So as can be seen rax is zero and naturally dereferencing it is also zero. What's interesting is the content of the btrf_path: struct btrfs_path { nodes = {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, slots = {1, 0, 0, 0, 0, 0, 0, 0}, locks = {0, 0, 0, 0, 0, 0, 0, 0}, reada = 0, lowest_level = 0, search_for_split = 0, keep_locks = 0, skip_locking = 0, leave_spinning = 0, search_commit_root = 0, need_commit_sem = 0, skip_release_on_error = 0 } Any ideas how come btrfs_path can be all zero, the one in the first slot comes from the increment in btrfs_next_old_item. Regards, Nikolay -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html