• Nikolay Borisov's avatar
    btrfs: Relinquish CPUs in btrfs_compare_trees · 6af112b1
    Nikolay Borisov authored
    When doing any form of incremental send the parent and the child trees
    need to be compared via btrfs_compare_trees. This  can result in long
    loop chains without ever relinquishing the CPU. This causes softlockup
    detector to trigger when comparing trees with a lot of items. Example
    report:
    
    watchdog: BUG: soft lockup - CPU#0 stuck for 24s! [snapperd:16153]
    CPU: 0 PID: 16153 Comm: snapperd Not tainted 5.2.9-1-default #1 openSUSE Tumbleweed (unreleased)
    Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
    pstate: 40000005 (nZcv daif -PAN -UAO)
    pc : __ll_sc_arch_atomic_sub_return+0x14/0x20
    lr : btrfs_release_extent_buffer_pages+0xe0/0x1e8 [btrfs]
    sp : ffff00001273b7e0
    Call trace:
     __ll_sc_arch_atomic_sub_return+0x14/0x20
     release_extent_buffer+0xdc/0x120 [btrfs]
     free_extent_buffer.part.0+0xb0/0x118 [btrfs]
     free_extent_buffer+0x24/0x30 [btrfs]
     btrfs_release_path+0x4c/0xa0 [btrfs]
     btrfs_free_path.part.0+0x20/0x40 [btrfs]
     btrfs_free_path+0x24/0x30 [btrfs]
     get_inode_info+0xa8/0xf8 [btrfs]
     finish_inode_if_needed+0xe0/0x6d8 [btrfs]
     changed_cb+0x9c/0x410 [btrfs]
     btrfs_compare_trees+0x284/0x648 [btrfs]
     send_subvol+0x33c/0x520 [btrfs]
     btrfs_ioctl_send+0x8a0/0xaf0 [btrfs]
     btrfs_ioctl+0x199c/0x2288 [btrfs]
     do_vfs_ioctl+0x4b0/0x820
     ksys_ioctl+0x84/0xb8
     __arm64_sys_ioctl+0x28/0x38
     el0_svc_common.constprop.0+0x7c/0x188
     el0_svc_handler+0x34/0x90
     el0_svc+0x8/0xc
    
    Fix this by adding a call to cond_resched at the beginning of the main
    loop in btrfs_compare_trees.
    
    Fixes: 7069830a ("Btrfs: add btrfs_compare_trees function")
    CC: stable@vger.kernel.org # 4.4+
    Reviewed-by: default avatarJohannes Thumshirn <jthumshirn@suse.de>
    Signed-off-by: default avatarNikolay Borisov <nborisov@suse.com>
    Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
    Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
    6af112b1
send.c 176 KB