Re: [PATCH] btrfs: qgroup: fix sleep from invalid context bug in update_qgroup_limit_item()

[David Sterba]

On Thu, Nov 10, 2022 at 10:13:42PM +0800, ChenXiaoSong wrote:
> Syzkaller reported BUG as follows:
> 
>   BUG: sleeping function called from invalid context at
>        include/linux/sched/mm.h:274
>   Call Trace:
>    <TASK>
>    dump_stack_lvl+0xcd/0x134
>    __might_resched.cold+0x222/0x26b
>    kmem_cache_alloc+0x2e7/0x3c0
>    update_qgroup_limit_item+0xe1/0x390
>    btrfs_qgroup_inherit+0x147b/0x1ee0
>    create_subvol+0x4eb/0x1710
>    btrfs_mksubvol+0xfe5/0x13f0
>    __btrfs_ioctl_snap_create+0x2b0/0x430
>    btrfs_ioctl_snap_create_v2+0x25a/0x520
>    btrfs_ioctl+0x2a1c/0x5ce0
>    __x64_sys_ioctl+0x193/0x200
>    do_syscall_64+0x35/0x80
> 
> Fix this by introducing __update_qgroup_limit_item() helper, allocate
> memory outside of the spin lock.
> 
> Signed-off-by: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>

Added to misc-next, thanks.

> +	path = btrfs_alloc_path();

btrfs_alloc_path uses fixed GFP_NOFS flags for kmem_cache_alloc but that
does not try to detect if it could sleep or not.