Re: please review snapshot corruption path with delayed metadata insertion

[Chris Mason <chris.mason@oracle.com>]

Excerpts from David Sterba's message of 2011-06-20 20:24:35 -0400:
> On Mon, Jun 20, 2011 at 08:41:39AM +0900, Tsutomu Itoh wrote:
> > (2011/06/19 13:34), Tsutomu Itoh wrote:
> > >> I've fixed this up by moving the delayed metadata run down into the
> > >> snapshot creation code, please take a look.  If nobody objects I'll have
> > >> this in the pull I send to Linus this weekend.
> > > 
> > 
> > > I ran my balance test script about 12 hours, any problem didn't occur.
> > 
> > But, following panics still occur if inode_cache is specified.
> > 
> > [75164.963860] btrfs: relocating block group 18551406592 flags 18
> > [75165.565282] btrfs: relocating block group 18282971136 flags 20
> > [75165.883577] ------------[ cut here ]------------
> > [75165.883779] kernel BUG at fs/btrfs/relocation.c:2502!
> > [75165.883992] invalid opcode: 0000 [#1] SMP
> > [75165.884002] CPU 0
> > [75165.884002] Modules linked in: autofs4 sunrpc 8021q garp stp llc cpufreq_ondemand acpi_cpufreq freq_table mperf ipv6 btrfs zlib_deflate crc32c libcrc32c ext3 jbd dm_mirror dm_region_hash dm_log dm_mod kvm uinput ppdev parport_pc parport sg pcspkr i2c_i801 i2c_core iTCO_wdt iTCO_vendor_support tg3 shpchp pci_hotplug i3000_edac edac_core ext4 mbcache jbd2 crc16 sd_mod crc_t10dif sr_mod cdrom megaraid_sas pata_acpi ata_generic ata_piix libata scsi_mod floppy [last unloaded: microcode]
> > [75165.884002]
> > [75165.884002] Pid: 18615, comm: btrfs Not tainted 3.0.0-rc3test #1 FUJITSU-SV      PRIMERGY            /D2399
> > [75165.884002] RIP: 0010:[<ffffffffa02dede3>]  [<ffffffffa02dede3>] do_relocation+0x163/0x44b [btrfs]
> > [75165.884002] RSP: 0018:ffff8801026f7a08  EFLAGS: 00010202
> > [75165.884002] RAX: 0000000000000001 RBX: ffff8801949e7c00 RCX: 0000000000000002
> > [75165.884002] RDX: 0000000000000001 RSI: 0000000000000001 RDI: 0000000000000000
> > [75165.884002] RBP: ffff8801026f7ad8 R08: 00000000000006c7 R09: ffff8801026f78f0
> > [75165.884002] R10: ffff88009f9d7800 R11: 0000000442149000 R12: ffff880037c99180
> > [75165.884002] R13: ffff880152695f30 R14: ffff88009f9d4800 R15: ffff88013cfdbf78
> > [75165.884002] FS:  00007f490c045740(0000) GS:ffff88019fc00000(0000) knlGS:0000000000000000
> > [75165.884002] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > [75165.884002] CR2: 00000033cfea6a60 CR3: 0000000100d47000 CR4: 00000000000006f0
> > [75165.884002] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [75165.884002] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > [75165.884002] Process btrfs (pid: 18615, threadinfo ffff8801026f6000, task ffff880102060000)
> > [75165.884002] Stack:
> > [75165.884002]  ffff88000516d000 ffff88009f9d7d80 00000001026f7a98 ffff880037c99180
> > [75165.884002]  ffff880037c991c0 000000019f9d7820 ffff88011bf09ba0 ffff88009f9d7800
> > [75165.884002]  ffff8801026f7ad8 ffff88011bf094c0 ffff88013cfdbf78 00ff88009f9d7800
> > [75165.884002] Call Trace:
> > [75165.884002]  [<ffffffffa02926ec>] ? block_rsv_add_bytes+0x24/0x4d [btrfs]
> > [75165.884002]  [<ffffffffa02e137a>] relocate_tree_blocks+0x2fb/0x4a9 [btrfs]
> > [75165.884002]  [<ffffffffa02de227>] ? add_tree_block+0xff/0x121 [btrfs]
> > [75165.884002]  [<ffffffffa02e1b13>] relocate_block_group+0x214/0x4dc [btrfs]
> > [75165.884002]  [<ffffffffa02e1f26>] btrfs_relocate_block_group+0x14b/0x285 [btrfs]
> > [75165.884002]  [<ffffffffa02c7183>] ? btrfs_relocate_chunk+0x4a4/0x50d [btrfs]
> > [75165.884002]  [<ffffffffa02c6d48>] btrfs_relocate_chunk+0x69/0x50d [btrfs]
> > [75165.884002]  [<ffffffffa028b3f5>] ? btrfs_item_key_to_cpu+0x1a/0x36 [btrfs]
> > [75165.884002]  [<ffffffffa02c0d0f>] ? read_extent_buffer+0xba/0xf6 [btrfs]
> > [75165.884002]  [<ffffffffa02c561a>] ? btrfs_item_key_to_cpu+0x2a/0x46 [btrfs]
> > [75165.884002]  [<ffffffffa02c77be>] btrfs_balance+0x1ca/0x219 [btrfs]
> > [75165.884002]  [<ffffffffa02cfcbd>] btrfs_ioctl+0x922/0xc19 [btrfs]
> > [75165.884002]  [<ffffffff810e88e4>] ? handle_mm_fault+0x233/0x24a
> > [75165.884002]  [<ffffffff813a6be5>] ? do_page_fault+0x340/0x3b2
> > [75165.884002]  [<ffffffff8111d828>] do_vfs_ioctl+0x474/0x4c3
> > [75165.884002]  [<ffffffff810ffe41>] ? virt_to_head_page+0xe/0x31
> > [75165.884002]  [<ffffffff811010e8>] ? kmem_cache_free+0x20/0xae
> > [75165.884002]  [<ffffffff8111d8cd>] sys_ioctl+0x56/0x79
> > [75165.884002]  [<ffffffff813aa302>] system_call_fastpath+0x16/0x1b
> > [75165.884002] Code: 00 00 48 8b 95 60 ff ff ff 45 31 c0 41 b9 01 00 00 00 4c 89 e9 4c 89 f6 4c 89 ff e8 52 15 fb ff 83 f8 00 0f 8c e6 02 00 00 74 04 <0f> 0b eb fe 48 8b 53 68 0f b6 43 70 48 85 d2 75 14 49 8b 54 c5
> > [75165.884002] RIP  [<ffffffffa02dede3>] do_relocation+0x163/0x44b [btrfs]
> > [75165.884002]  RSP <ffff8801026f7a08>
> > 
> > (gdb) l *do_relocation+0x163
> > 0x58e07 is in do_relocation (fs/btrfs/relocation.c:2502).
> > 2497                            ret = btrfs_search_slot(trans, root, key, path, 0, 1);
> > 2498                            if (ret < 0) {
> > 2499                                    err = ret;
> > 2500                                    break;
> > 2501                            }
> > 2502                            BUG_ON(ret > 0);
> 
> this translates btrfs_search_slot() result to
> 
> 1600  * If the key isn't found, the path points to the slot where it should
> 1601  * be inserted, and 1 is returned.  If there are other errors during the
> 1602  * search a negative error number is returned.
> 
> ie. the key is not in the tree. If you can reproduce it reliably, add
> some printks about the key and path's ->search_commit_root,
> ->skip_locking, and ->leave_spinning which are accessed within
> btrfs_search_slot().

With the inode cache on, this is the expected result right now.  It is
changing the tree after the snapshot is taken, which isn't allowed.  I'm
hoping to nail it down this week.

-chris