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

[David Sterba]

On Fri, Nov 11, 2022 at 07:31:22AM +0800, Qu Wenruo wrote:
> 
> 
> On 2022/11/11 04:54, David Sterba wrote:
> > 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.
> 
> Please remove it for now, the patch only addressed what MM layer 
> reports, it doesn't really solve the root cause, we're doing a tree 
> modification (btrfs_search_slot()), under a spinlock.

Removed. As the potential sleeping under spinlock is hard to spot we
should add might_sleep to some places.