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Subject: Re: [PATCH v7 1/2] btrfs: Fix metadata underflow caused by
 btrfs_reloc_clone_csum error
To: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>,
        "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
        <fdmanana@suse.com>
References: <20170308022552.14686-1-quwenruo@cn.fujitsu.com>
 <d4241168-4adf-6f36-af61-0487f7e74f91@profihost.ag>
From: Qu Wenruo <quwenruo@cn.fujitsu.com>
Message-ID: <03d57894-e8df-1001-b57a-daa205037f1c@cn.fujitsu.com>
Date: Mon, 13 Mar 2017 09:16:57 +0800
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At 03/13/2017 04:49 AM, Stefan Priebe - Profihost AG wrote:
> Hi Qu,
>
> while V5 was running fine against the openSUSE-42.2 kernel (based on v4.4).

Thanks for the test.

>
> V7 results in OOPS to me:
> BUG: unable to handle kernel NULL pointer dereference at 00000000000001f0

This 0x1f0 is the same as offsetof(struct brrfs_root, fs_info), quite 
nice clue.

> IP: [<ffffffffc03dde23>] __endio_write_update_ordered+0x33/0x140 [btrfs]

IP points to:
---
static inline bool btrfs_is_free_space_inode(struct btrfs_inode *inode)
{
         struct btrfs_root *root = inode->root; << Either here

         if (root == root->fs_info->tree_root && << Or here
             btrfs_ino(inode) != BTRFS_BTREE_INODE_OBJECTID)

---

Taking the above offset into consideration, it's only possible for later 
case.

So here, we have a btrfs_inode whose @root is NULL.

This can be fixed easily by checking @root inside 
btrfs_is_free_space_inode(), as the backtrace shows that it's only 
happening for DirectIO, and it won't happen for free space cache inode.

But I'm more curious how this happened for a more accurate fix, or we 
could have other NULL pointer access.

Did you have any reproducer for this?

Thanks,
Qu

> PGD 14e18d4067 PUD 14e1868067 PMD 0
> Oops: 0000 [#1] SMP
> Modules linked in: netconsole xt_multiport ipt_REJECT nf_reject_ipv4
> xt_set iptable_filter ip_tables x_tables ip_set_hash_net ip_set
> nfnetlink crc32_pclmul button loop btrfs xor usbhid raid6_pq ata_generic
> virtio_blk virtio_net uhci_hcd ehci_hcd i2c_piix4 usbcore virtio_pci
> i2c_core usb_common ata_piix floppy
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.52+112-ph #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 1.7.5-20140722_172050-sagunt 04/01/2014
> task: ffffffffb4e0f500 ti: ffffffffb4e00000 task.ti: ffffffffb4e00000
> RIP: 0010:[<ffffffffc03dde23>] [<ffffffffc03dde23>]
> __endio_write_update_ordered+0x33/0x140 [btrfs]
> RSP: 0018:ffff8814eae03cd8 EFLAGS: 00010086
> RAX: 0000000000000000 RBX: ffff8814e8fd5aa8 RCX: 0000000000000001
> RDX: 0000000000100000 RSI: 0000000000100000 RDI: ffff8814e45885c0
> RBP: ffff8814eae03d10 R08: ffff8814e8334000 R09: 000000018040003a
> R10: ffffea00507d8d00 R11: ffff88141f634080 R12: ffff8814e45885c0
> R13: ffff8814e125d700 R14: 0000000000100000 R15: ffff8800376c6a80
> FS: 0000000000000000(0000) GS:ffff8814eae00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000000001f0 CR3: 00000014e34c9000 CR4: 00000000001406f0Stack:
> 0000000000000000 0000000000100000 ffff8814e8fd5aa8 ffff8814e953f3c0
> ffff8814e125d700 0000000000100000 ffff8800376c6a80 ffff8814eae03d38
> ffffffffc03ddf67 ffff8814e86b6a80 ffff8814e8fd5aa8 0000000000000001
> Call Trace:
> [<ffffffffc03ddf67>] btrfs_endio_direct_write+0x37/0x60 [btrfs]
> [<ffffffffb438f2f7>] bio_endio+0x57/0x60
> [<ffffffffc04082c1>] btrfs_end_bio+0xa1/0x140 [btrfs]
> [<ffffffffb438f2f7>] bio_endio+0x57/0x60
> [<ffffffffb439763b>] blk_update_request+0x8b/0x330
> [<ffffffffb43a05ba>] blk_mq_end_request+0x1a/0x70
> [<ffffffffc039f30f>] virtblk_request_done+0x3f/0x70 [virtio_blk]
> [<ffffffffb43a0688>] __blk_mq_complete_request+0x78/0xe0
> [<ffffffffb43a070c>] blk_mq_complete_request+0x1c/0x20
> [<ffffffffc039f184>] virtblk_done+0x64/0xe0 [virtio_blk]
> [<ffffffffb446dd2a>] vring_interrupt+0x3a/0x90
> [<ffffffffb40d3fe9>] __handle_irq_event_percpu+0x89/0x1b0
> [<ffffffffb40d4133>] handle_irq_event_percpu+0x23/0x60
> [<ffffffffb40d41ab>] handle_irq_event+0x3b/0x60
> [<ffffffffb40d74ef>] handle_edge_irq+0x6f/0x150
> [<ffffffffb4007cad>] handle_irq+0x1d/0x30
> [<ffffffffb400750b>] do_IRQ+0x4b/0xd0
> [<ffffffffb46af8cc>] common_interrupt+0x8c/0x8c
> DWARF2 unwinder stuck at ret_from_intr+0x0/0x1b
> Leftover inexact backtrace:
> 2017-03-12 20:33:08     <IRQ><EOI>
> 2017-03-12 20:33:08      [<ffffffffb404ba46>] ? native_safe_halt+0x6/0x10
> [<ffffffffb400fa3e>] default_idle+0x1e/0xe0
> [<ffffffffb401021f>] arch_cpu_idle+0xf/0x20
> [<ffffffffb40c67eb>] default_idle_call+0x3b/0x40
> [<ffffffffb40c6a8a>] cpu_startup_entry+0x29a/0x370
> [<ffffffffb46a358c>] rest_init+0x7c/0x80
> [<ffffffffb4f67fa5>] start_kernel+0x490/0x49d
> [<ffffffffb4f67120>] ? early_idt_handler_array+0x120/0x120
> [<ffffffffb4f674b3>] x86_64_start_reservations+0x2a/0x2c
> [<ffffffffb4f675f0>] x86_64_start_kernel+0x13b/0x14a
> Code: e5 41 57 41 56 41 55 41 54 49 89 fc 53 48 83 ec 10 48 8b 87 70 fc
> ff ff 4c 8b 87 38 fe ff ff 48 c7 45 c8 00 00 00 00 48 89 75 d0 <48> 8b
> b8 f0 01 00 00 48 3b 47 28 49 8b 84 24 78 fc ff ff 0f 84
> RIP [<ffffffffc03dde23>] __endio_write_update_ordered+0x33/0x140 [btrfs]
> RSP <ffff8814eae03cd8>
> CR2: 00000000000001f0
> ---[ end trace 7529a0652fd7873e ]---
> Kernel panic - not syncing: Fatal exception in interrupt
> Kernel Offset: 0x33000000 from 0xffffffff81000000 (relocation range:
> 0xffffffff80000000-0xffffffffbfffffff)
>
> Greets,
> Stefan
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