On Wed, Nov 26, 2014 at 3:57 PM, Josef Bacik <jba...@fb.com> wrote:
> On 11/26/2014 10:28 AM, Filipe Manana wrote:
>>
>> If we remove a block group (because it became empty), we might have left
>> a caching_ctl structure in fs_info->caching_block_groups that points to
>> the block group and is accessed at transaction commit time. This results
>> in accessing an invalid or incorrect block group. This issue became
>> visible
>> after Josef's patch "Btrfs: remove empty block groups automatically".
>>
>> So if the block group is removed make sure we don't leave a dangling
>> caching_ctl in caching_block_groups.
>>
>> Sample crash trace:
>>
>> [58380.439449] BUG: unable to handle kernel paging request at
>> ffff8801446eaeb8
>> [58380.439707] IP: [<ffffffffa03f6d05>]
>> block_group_cache_done.isra.21+0xc/0x1c [btrfs]
>> [58380.440879] PGD 1acb067 PUD 23f5ff067 PMD 23f5db067 PTE
>> 80000001446ea060
>> [58380.441220] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
>> [58380.441486] Modules linked in: btrfs crc32c_generic xor raid6_pq nfsd
>> auth_rpcgss oid_registry nfs_acl nfs lockd fscache sunrpc loop psmouse
>> processor i2c_piix4 parport_pc parport pcspkr serio_raw evdev i2ccore
>> thermal_sys microcode button ext4 crc16 jbd2 mbcache sr_mod cdrom
>> ata_generic sg sd_mod crc_t10dif crct10dif_generic crct10dif_common
>> virtio_scsi floppy ata_piix e1000 libata virtio_pci scsi_mod virtio_ring
>> virtio [last unloaded: btrfs]
>> [58380.443238] CPU: 3 PID: 25728 Comm: btrfs-transacti Tainted: G W
>> 3.17.0-rc5-btrfs-next-1+ #1
>> [58380.443238] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>> rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
>> [58380.443238] task: ffff88013ac82090 ti: ffff88013896c000 task.ti:
>> ffff88013896c000
>> [58380.443238] RIP: 0010:[<ffffffffa03f6d05>] [<ffffffffa03f6d05>]
>> block_group_cache_done.isra.21+0xc/0x1c [btrfs]
>> [58380.443238] RSP: 0018:ffff88013896fdd8 EFLAGS: 00010283
>> [58380.443238] RAX: ffff880222cae850 RBX: ffff880119ba74c0 RCX:
>> 0000000000000000
>> [58380.443238] RDX: 0000000000000000 RSI: ffff880185e16800 RDI:
>> ffff8801446eaeb8
>> [58380.443238] RBP: ffff88013896fdd8 R08: ffff8801a9ca9fa8 R09:
>> ffff88013896fc60
>> [58380.443238] R10: ffff88013896fd28 R11: 0000000000000000 R12:
>> ffff880222cae000
>> [58380.443238] R13: ffff880222cae850 R14: ffff880222cae6b0 R15:
>> ffff8801446eae00
>> [58380.443238] FS: 0000000000000000(0000) GS:ffff88023ed80000(0000)
>> knlGS:0000000000000000
>> [58380.443238] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> [58380.443238] CR2: ffff8801446eaeb8 CR3: 0000000001811000 CR4:
>> 00000000000006e0
>> [58380.443238] Stack:
>> [58380.443238] ffff88013896fe18 ffffffffa03fe2d5 ffff880222cae850
>> ffff880185e16800
>> [58380.443238] ffff88000dc41c20 0000000000000000 ffff8801a9ca9f00
>> 0000000000000000
>> [58380.443238] ffff88013896fe80 ffffffffa040fbcf ffff88018b0dcdb0
>> ffff88013ac82090
>> [58380.443238] Call Trace:
>> [58380.443238] [<ffffffffa03fe2d5>] btrfs_prepare_extent_commit+0x5a/0xd7
>> [btrfs]
>> [58380.443238] [<ffffffffa040fbcf>] btrfs_commit_transaction+0x45c/0x882
>> [btrfs]
>> [58380.443238] [<ffffffffa040c058>] transaction_kthread+0xf2/0x1a4
>> [btrfs]
>> [58380.443238] [<ffffffffa040bf66>] ?
>> btrfs_cleanup_transaction+0x3d8/0x3d8 [btrfs]
>> [58380.443238] [<ffffffff8105966b>] kthread+0xb7/0xbf
>> [58380.443238] [<ffffffff810595b4>] ? __kthread_parkme+0x67/0x67
>> [58380.443238] [<ffffffff813ebeac>] ret_from_fork+0x7c/0xb0
>> [58380.443238] [<ffffffff810595b4>] ? __kthread_parkme+0x67/0x67
>>
>> Signed-off-by: Filipe Manana <fdman...@suse.com>
>> ---
>> fs/btrfs/ctree.h | 1 +
>> fs/btrfs/extent-tree.c | 27 +++++++++++++++++++++++++++
>> 2 files changed, 28 insertions(+)
>>
>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>> index d3ccd09..7f40a65 100644
>> --- a/fs/btrfs/ctree.h
>> +++ b/fs/btrfs/ctree.h
>> @@ -1277,6 +1277,7 @@ struct btrfs_block_group_cache {
>> unsigned int ro:1;
>> unsigned int dirty:1;
>> unsigned int iref:1;
>> + unsigned int has_caching_ctl:1;
>>
>
> Don't do this, just unconditionally call get_caching_control in
> btrfs_remove_block_group, then if we get something we can do stuff,
> otherwise we can just continue. Thanks,
That's what I initially thought too. However, get_caching_control only
returns us the caching_ctl if block_group->cached ==
BTRFS_CACHE_STARTED, so it's not enough to use it exclusively. The
has_caching_ctl flag is just to avoid holding the semaphore and search
through the list (since block_group->caching_ctl can be NULL but a
caching_ctl point to the block group can be in the list).
>
> Josef
>
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--
Filipe David Manana,
"Reasonable men adapt themselves to the world.
Unreasonable men adapt the world to themselves.
That's why all progress depends on unreasonable men."
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