On Wed, Feb 01, 2017 at 11:01:28PM +0000, fdman...@kernel.org wrote:
> From: Filipe Manana <fdman...@suse.com>
>
> At close_ctree() we free the block groups and then only after we wait for
> any running worker kthreads to finish and shutdown the workqueues. This
> behaviour is racy and it triggers an assertion failure when freeing block
> groups because while we are doing it we can have for example a block group
> caching kthread running, and in that case the block group's reference
> count is greater than 1, leading to an assertion failure:
>
> [19041.198004] assertion failed: atomic_read(&block_group->count) == 1, file:
> fs/btrfs/extent-tree.c, line: 9799
> [19041.200584] ------------[ cut here ]------------
> [19041.201692] kernel BUG at fs/btrfs/ctree.h:3418!
> [19041.202830] invalid opcode: 0000 [#1] PREEMPT SMP
> [19041.203929] Modules linked in: btrfs xor raid6_pq dm_flakey dm_mod
> crc32c_generic ppdev sg psmouse acpi_cpufreq pcspkr parport_pc evdev tpm_tis
> parport tpm_tis_core i2c_piix4 i2c_core tpm serio_raw processor button loop
> autofs4 ext4 crc16 jbd2 mbcache sr_mod cdrom sd_mod ata_generic virtio_scsi
> ata_piix virtio_pci libata virtio_ring virtio e1000 scsi_mod floppy [last
> unloaded: btrfs]
> [19041.208082] CPU: 6 PID: 29051 Comm: umount Not tainted
> 4.9.0-rc7-btrfs-next-36+ #1
> [19041.208082] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.9.1-0-gb3ef39f-prebuilt.qemu-project.org 04/01/2014
> [19041.208082] task: ffff88015f028980 task.stack: ffffc9000ad34000
> [19041.208082] RIP: 0010:[<ffffffffa03e319e>] [<ffffffffa03e319e>]
> assfail.constprop.41+0x1c/0x1e [btrfs]
> [19041.208082] RSP: 0018:ffffc9000ad37d60 EFLAGS: 00010286
> [19041.208082] RAX: 0000000000000061 RBX: ffff88015ecb4000 RCX:
> 0000000000000001
> [19041.208082] RDX: ffff88023f392fb8 RSI: ffffffff817ef7ba RDI:
> 00000000ffffffff
> [19041.208082] RBP: ffffc9000ad37d60 R08: 0000000000000001 R09:
> 0000000000000000
> [19041.208082] R10: ffffc9000ad37cb0 R11: ffffffff82f2b66d R12:
> ffff88023431d170
> [19041.208082] R13: ffff88015ecb40c0 R14: ffff88023431d000 R15:
> ffff88015ecb4100
> [19041.208082] FS: 00007f44f3d42840(0000) GS:ffff88023f380000(0000)
> knlGS:0000000000000000
> [19041.208082] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [19041.208082] CR2: 00007f65d623b000 CR3: 00000002166f2000 CR4:
> 00000000000006e0
> [19041.208082] Stack:
> [19041.208082] ffffc9000ad37d98 ffffffffa035989f ffff88015ecb4000
> ffff88015ecb5630
> [19041.208082] ffff88014f6be000 0000000000000000 00007ffcf0ba6a10
> ffffc9000ad37df8
> [19041.208082] ffffffffa0368cd4 ffff88014e9658e0 ffffc9000ad37e08
> ffffffff811a634d
> [19041.208082] Call Trace:
> [19041.208082] [<ffffffffa035989f>] btrfs_free_block_groups+0x17f/0x392
> [btrfs]
> [19041.208082] [<ffffffffa0368cd4>] close_ctree+0x1c5/0x2e1 [btrfs]
> [19041.208082] [<ffffffff811a634d>] ? evict_inodes+0x132/0x141
> [19041.208082] [<ffffffffa034356d>] btrfs_put_super+0x15/0x17 [btrfs]
> [19041.208082] [<ffffffff8118fc32>] generic_shutdown_super+0x6a/0xeb
> [19041.208082] [<ffffffff8119004f>] kill_anon_super+0x12/0x1c
> [19041.208082] [<ffffffffa0343370>] btrfs_kill_super+0x16/0x21 [btrfs]
> [19041.208082] [<ffffffff8118fad1>] deactivate_locked_super+0x3b/0x68
> [19041.208082] [<ffffffff8118fb34>] deactivate_super+0x36/0x39
> [19041.208082] [<ffffffff811a9946>] cleanup_mnt+0x58/0x76
> [19041.208082] [<ffffffff811a99a2>] __cleanup_mnt+0x12/0x14
> [19041.208082] [<ffffffff81071573>] task_work_run+0x6f/0x95
> [19041.208082] [<ffffffff81001897>] prepare_exit_to_usermode+0xa3/0xc1
> [19041.208082] [<ffffffff81001a23>] syscall_return_slowpath+0x16e/0x1d2
> [19041.208082] [<ffffffff814c607d>] entry_SYSCALL_64_fastpath+0xab/0xad
> [19041.208082] Code: c7 ae a0 3e a0 48 89 e5 e8 4e 74 d4 e0 0f 0b 55 89 f1 48
> c7 c2 0b a4 3e a0 48 89 fe 48 c7 c7 a4 a6 3e a0 48 89 e5 e8 30 74 d4 e0 <0f>
> 0b 55 31 d2 48 89 e5 e8 d5 b9 f7 ff 5d c3 48 63 f6 55 31 c9
> [19041.208082] RIP [<ffffffffa03e319e>] assfail.constprop.41+0x1c/0x1e
> [btrfs]
> [19041.208082] RSP <ffffc9000ad37d60>
> [19041.279264] ---[ end trace 23330586f16f064d ]---
>
> This started happening as of kernel 4.8, since commit f3bca8028bd9
> ("Btrfs: add ASSERT for block group's memory leak") introduced these
> assertions.
>
> So fix this by freeing the block groups only after waiting for all
> worker kthreads to complete and shutdown the workqueues.
This looks good to me, but I don't understand how that could happen, if
a block group is being cached by the caching worker thread, the block
group cache has been marked as BTRFS_CACHE_STARTED so we should wait on
wait_block_group_cache_done() in btrfs_free_block_groups() before
getting to the ASSERT. Maybe something else broke?
Thanks,
-liubo
>
> Signed-off-by: Filipe Manana <fdman...@suse.com>
> ---
> fs/btrfs/disk-io.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index 066d9b9..a90e40e 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -3985,8 +3985,6 @@ void close_ctree(struct btrfs_fs_info *fs_info)
>
> btrfs_put_block_group_cache(fs_info);
>
> - btrfs_free_block_groups(fs_info);
> -
> /*
> * we must make sure there is not any read request to
> * submit after we stopping all workers.
> @@ -3994,6 +3992,13 @@ void close_ctree(struct btrfs_fs_info *fs_info)
> invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
> btrfs_stop_all_workers(fs_info);
>
> + /*
> + * Free block groups only after stopping all workers, since we could
> + * have block group caching kthreads running, and therefore they could
> + * race with us if we freed the block groups before stopping them.
> + */
> + btrfs_free_block_groups(fs_info);
> +
> clear_bit(BTRFS_FS_OPEN, &fs_info->flags);
> free_root_pointers(fs_info, 1);
>
> --
> 2.7.0.rc3
>
> --
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