Hi Filipe,

On Mon, Sep 05, 2016 at 04:28:09PM +0100, Filipe Manana wrote:

On Fri, Sep 2, 2016 at 8:35 PM, Liu Bo [off-list ref] wrote:

quoted

This can only happen with CONFIG_BTRFS_FS_CHECK_INTEGRITY=y.

Commit 1ba98d0 ("Btrfs: detect corruption when non-root leaf has zero item")
assumes that a leaf is its root when leaf->bytenr == btrfs_root_bytenr(root),
however, we should not use btrfs_root_bytenr(root) since it's mainly got
updated during committing transaction.  So the check can fail when doing
COW on this leaf while it is a root.

This changes to use "if (leaf == btrfs_root_node(root))" instead, just like
how we check whether leaf is a root in __btrfs_cow_block().

Reported-by: Jeff Mahoney <redacted>
Signed-off-by: Liu Bo <redacted>

Hi Bo,

Even with this patch applied against latest branch for-linus-4.8, at
least on a build with CONFIG_BTRFS_FS_CHECK_INTEGRITY=y,
the issue still happens for me when running fsstress with balance in parallel:

Thanks for the report.

This panic shows that we can have non-root btree leaf with 0 nritems during
split_leaf(), but a btrfs_search_slot which calls split_leaf() like this is
inserting an item, and while we set @right's nritems to 0, we also assign @disk_key
associated with @right in the parent node, so I think we're actually having
 nritem 0 temporarily and we can remove this btrfs_mark_buffer_dirty() like the
following quick patch.

Thanks,

-liubo

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index d1c56c9..5e5ceb5 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c

@@ -4341,7 +4341,11 @@ again:
 			if (path->slots[1] == 0)
 				fixup_low_keys(fs_info, path, &disk_key, 1);
 		}
-		btrfs_mark_buffer_dirty(right);
+		/*
+		 * We create a new leaf 'right' for the required ins_len and
+		 * we'll do btrfs_mark_buffer_dirty() on this leaf after copying
+		 * the content of ins_len to 'right'.
+		 */
 		return ret;
 	}
 

[  366.998044] BTRFS: device fsid 69759b3a-96ae-467d-aa63-364144e73a28
devid 1 transid 3 /dev/sdc
[  367.023652] BTRFS info (device sdc): turning on discard
[  367.025036] BTRFS info (device sdc): disk space caching is enabled
[  367.026360] BTRFS info (device sdc): has skinny extents
[  367.069415] BTRFS info (device sdc): creating UUID tree
[  367.133704] BTRFS info (device sdc): relocating block group 29360128 flags 36
[  367.142196] BTRFS info (device sdc): found 2 extents
[  367.147932] BTRFS info (device sdc): relocating block group 20971520 flags 34
[  367.157947] BTRFS info (device sdc): found 1 extents
[  367.162649] BTRFS info (device sdc): relocating block group 12582912 flags 1
[  367.182872] BTRFS info (device sdc): found 1 extents
[  367.189932] BTRFS info (device sdc): found 1 extents
[  367.200983] BTRFS info (device sdc): relocating block group
1270874112 flags 1
[  367.235862] BTRFS critical (device sdc): corrupt leaf, non-root
leaf's nritems is 0: block=1103937536,root=5, slot=0
[  367.238223] BTRFS info (device sdc): leaf 1103937536 total ptrs 0
free space 3995
[  367.239371] BTRFS: assertion failed: 0, file: fs/btrfs/disk-io.c, line: 4059
[  367.240321] ------------[ cut here ]------------
[  367.241245] kernel BUG at fs/btrfs/ctree.h:3367!
[  367.241961] invalid opcode: 0000 [#1] PREEMPT SMP
[  367.242685] Modules linked in: btrfs crc32c_generic xor raid6_pq
acpi_cpufreq tpm_tis tpm sg i2c_piix4 i2c_core psmouse ppdev processor
evdev parport_pc parport serio_raw pcspkr button loop autofs4 ext4
crc16 jbd2 mbcache sr_mod cdrom sd_mod ata_generic virtio_scsi
ata_piix libata virtio_pci virtio_ring e1000 virtio scsi_mod floppy
[last unloaded: btrfs]
[  367.244302] CPU: 11 PID: 3451 Comm: fdm-stress Not tainted
4.7.0-rc6-btrfs-next-34+ #1
[  367.244302] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
[  367.244302] task: ffff880183ef8bc0 ti: ffff880183fe0000 task.ti:
ffff880183fe0000
[  367.244302] RIP: 0010:[<ffffffffa04601d5>]  [<ffffffffa04601d5>]
assfail.constprop.42+0x1c/0x1e [btrfs]
[  367.244302] RSP: 0018:ffff880183fe3c78  EFLAGS: 00010296
[  367.244302] RAX: 0000000000000040 RBX: ffff880222a66ab0 RCX: 0000000000000001
[  367.244302] RDX: ffffffff810a0a23 RSI: ffffffff814a82cb RDI: 00000000ffffffff
[  367.244302] RBP: ffff880183fe3c78 R08: 0000000000000001 R09: 0000000000000000
[  367.244302] R10: ffff880183fe3b70 R11: ffffffff82f3650d R12: ffff880183e8e000
[  367.244302] R13: ffff8800b3e7d000 R14: 0000000000000a59 R15: 0000000000000017
[  367.244302] FS:  00007f0b85310700(0000) GS:ffff88023f4c0000(0000)
knlGS:0000000000000000
[  367.244302] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  367.244302] CR2: 00007f0b7800ea28 CR3: 000000022da9b000 CR4: 00000000000006e0
[  367.244302] Stack:
[  367.244302]  ffff880183fe3ca0 ffffffffa03e51e3 0000000000000023
ffff880222a66ab0
[  367.244302]  ffff880183885bb8 ffff880183fe3d38 ffffffffa03c9540
0000000083fe3d08
[  367.244302]  ffff8800b3e7d2d8 0000000000001000 ffff880183fe3e7f
ffff880183ff8000
[  367.244302] Call Trace:
[  367.244302]  [<ffffffffa03e51e3>] btrfs_mark_buffer_dirty+0xdf/0xe5 [btrfs]
[  367.244302]  [<ffffffffa03c9540>] split_leaf+0x47c/0x566 [btrfs]
[  367.244302]  [<ffffffffa03c9c09>] btrfs_search_slot+0x5df/0x755 [btrfs]
[  367.244302]  [<ffffffff8116daf7>] ? slab_post_alloc_hook+0x42/0x52
[  367.244302]  [<ffffffffa03caf5a>] btrfs_insert_empty_items+0x5d/0xa6 [btrfs]
[  367.244302]  [<ffffffffa03f783b>] btrfs_symlink+0x17f/0x34f [btrfs]
[  367.244302]  [<ffffffff8118bcf5>] vfs_symlink+0x51/0x6e
[  367.244302]  [<ffffffff8118fc4c>] SYSC_symlinkat+0x6d/0xb2
[  367.244302]  [<ffffffff8100101a>] ? trace_hardirqs_on_thunk+0x1a/0x1c
[  367.244302]  [<ffffffff811904b6>] SyS_symlink+0x16/0x18
[  367.244302]  [<ffffffff814a88e5>] entry_SYSCALL_64_fastpath+0x18/0xa8
[  367.244302]  [<ffffffff81102507>] ? time_hardirqs_off+0x9/0x14
[  367.244302]  [<ffffffff8108f019>] ? trace_hardirqs_off_caller+0x1f/0xaa
[  367.244302] Code: 89 83 88 00 00 00 31 c0 5b 41 5c 41 5d 5d c3 55
89 f1 48 c7 c2 14 8b 46 a0 48 89 fe 48 c7 c7 27 8c 46 a0 48 89 e5 e8
e5 2f cc e0 <0f> 0b 55 89 f1 48 c7 c2 03 a2 46 a0 48 89 fe 48 c7 c7 dc
a3 46
[  367.244302] RIP  [<ffffffffa04601d5>] assfail.constprop.42+0x1c/0x1e [btrfs]
[  367.244302]  RSP <ffff880183fe3c78>
[  367.289039] ---[ end trace a3e4ce9819ed383b ]---


thanks

quoted

---
 fs/btrfs/disk-io.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 9367c31..b401e6d 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c

@@ -572,13 +572,17 @@ static noinline int check_leaf(struct btrfs_root *root,
                 * open_ctree() some roots has not yet been set up.
                 */
                if (!IS_ERR_OR_NULL(check_root)) {
+                       struct extent_buffer *eb;
+
+                       eb = btrfs_root_node(check_root);
                        /* if leaf is the root, then it's fine */
-                       if (leaf->start !=
-                           btrfs_root_bytenr(&check_root->root_item)) {
+                       if (leaf != eb) {
                                CORRUPT("non-root leaf's nritems is 0",
-                                       leaf, root, 0);
+                                       leaf, check_root, 0);
+                               free_extent_buffer(eb);
                                return -EIO;
                        }
+                       free_extent_buffer(eb);
                }
                return 0;
        }
--

2.5.5

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-- 
Filipe David Manana,

"People will forget what you said,
 people will forget what you did,
 but people will never forget how you made them feel."