On Wed, Jan 16, 2013 at 6:36 AM, Liu Bo <bo.li.liu@xxxxxxxxxx> wrote:
> This comes from one of btrfs's project ideas,
> As we defragment files, we break any sharing from other snapshots.
> The balancing code will preserve the sharing, and defrag needs to grow this
> as well.
>
> Now we're able to fill the blank with this patch, in which we make full use of
> backref walking stuff.
>
> Here is the basic idea,
> o set the writeback ranges started by defragment with flag EXTENT_DEFRAG
> o at endio, after we finish updating fs tree, we use backref walking to find
> all parents of the ranges and re-link them with the new COWed file layout by
> adding corresponding backrefs.
>
> Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
> Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> ---
> v4->v5:
> - Clarify the comments for duplicated refs.
> - Clear defrag flag after we're ready to defrag.
> - Fix a bug on HOLE extent.
> v3->v4:
> - Fix duplicated refs bugs detected by mounting with autodefrag, thanks
> for the bug report from Mitch and Chris.
> v2->v3:
> - Rebase
> v1->v2:
> - Address comments from David.
>
I've been testing this patch on a 3.7.2 kernel merged with the
for-linus branch for the 3.8_rc kernels, and I'm seeing the following
error:
[16028.159400] general protection fault: 0000 [#1] SMP
[16028.159461] Modules linked in: ipv6 snd_hda_codec_analog
snd_hda_intel snd_hda_codec tg3 snd_hwdep snd_pcm snd_page_alloc
snd_timer snd sr_mod ppdev parport_pc parport microcode iTCO_wdt
iTCO_vendor_support floppy lpc_ich i2c_i801 serio_raw pcspkr
ablk_helper cryptd lrw xts gf128mul aes_x86_64 sha256_generic fuse xfs
nfs lockd sunrpc reiserfs btrfs zlib_deflate ext4 jbd2 ext3 jbd ext2
mbcache sl811_hcd hid_generic xhci_hcd ohci_hcd uhci_hcd ehci_hcd
[16028.159952] CPU 0
[16028.159975] Pid: 4420, comm: btrfs-cleaner Not tainted 3.7.2-sad+
#4 Dell Inc. OptiPlex 745 /0WF810
[16028.160002] RIP: 0010:[<ffffffffa017b4f2>] [<ffffffffa017b4f2>]
btrfs_clean_old_snapshots+0xa6/0x12c [btrfs]
[16028.160002] RSP: 0000:ffff880078609e38 EFLAGS: 00010282
[16028.160002] RAX: dead000000200200 RBX: ffff880000000000 RCX: 0000000000018e20
[16028.160002] RDX: dead000000100100 RSI: 000000000000001b RDI: 000000000000001b
[16028.160002] RBP: ffff880078609e78 R08: 00000000001c001b R09: ffffffffa015aa01
[16028.160002] R10: ffffffffa016bbbd R11: ffff8800183a4800 R12: 0000160000000000
[16028.160002] R13: ffff880078609e38 R14: ffff8800183a4800 R15: ffff8800183a4c38
[16028.160002] FS: 0000000000000000(0000) GS:ffff88007f200000(0000)
knlGS:0000000000000000
[16028.160002] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[16028.160002] CR2: 00007f64f5214d96 CR3: 0000000011ef2000 CR4: 00000000000007f0
[16028.160002] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[16028.160002] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[16028.160002] Process btrfs-cleaner (pid: 4420, threadinfo
ffff880078608000, task ffff88007ca62120)
[16028.160002] Stack:
[16028.160002] ffff8800183a4c38 ffff8800020e3c38 ffff880078609e48
ffff88007921b800
[16028.160002] ffff88007ca62120 ffff88007ca62120 ffff88007ca62120
0000000000000000
[16028.160002] ffff880078609eb8 ffffffffa0173f68 ffff88007921b800
0000000000000000
[16028.160002] Call Trace:
[16028.160002] [<ffffffffa0173f68>] cleaner_kthread+0x5a/0xe6 [btrfs]
[16028.160002] [<ffffffffa0173f0e>] ? transaction_kthread+0x1a0/0x1a0 [btrfs]
[16028.160002] [<ffffffff8104c9c3>] kthread+0xba/0xc2
[16028.160002] [<ffffffff8104c909>] ? kthread_freezable_should_stop+0x52/0x52
[16028.160002] [<ffffffff815f9d9c>] ret_from_fork+0x7c/0xb0
[16028.160002] [<ffffffff8104c909>] ? kthread_freezable_should_stop+0x52/0x52
[16028.160002] Code: 49 bc 00 00 00 00 00 16 00 00 48 bb 00 00 00 00
00 88 ff ff eb 7d 4d 8d b7 c8 fb ff ff 4d 85 ff 75 02 0f 0b 49 8b 17
49 8b 47 08 <48> 89 42 08 48 89 10 48 be 00 01 10 00 00 00 ad de 49 89
37 48
[16028.160002] RIP [<ffffffffa017b4f2>]
btrfs_clean_old_snapshots+0xa6/0x12c [btrfs]
[16028.160002] RSP <ffff880078609e38>
[16028.170584] ---[ end trace 4034e68ac40e6c2b ]---
Using gdb to identify the location of the GPF gives me the following:
(gdb) list *(btrfs_clean_old_snapshots+0xa6)
0x2a4f2 is in btrfs_clean_old_snapshots (include/linux/list.h:88).
83 * This is only for internal list manipulation where we know
84 * the prev/next entries already!
85 */
86 static inline void __list_del(struct list_head * prev, struct
list_head * next)
87 {
88 next->prev = prev;
89 prev->next = next;
90 }
91
92 /**
I've tried to trap the error with a BUG_ON prior to deleting the list,
but my attempt isn't catching the error:
@@ -1769,6 +1769,7 @@ int btrfs_clean_old_snapshots(struct btrfs_root *root)
int ret;
root = list_entry(list.next, struct btrfs_root, root_list);
+ BUG_ON(&root->root_list == NULL);
list_del(&root->root_list);
btrfs_kill_all_delayed_nodes(root);
--
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