Re: [PATCH v2] btrfs: qgroup: fix sleep from invalid context bug in update_qgroup_limit_item()

[ChenXiaoSong]

Thanks for your suggestions, I will try to send a new version patch.

在 2022/11/11 17:09, Qu Wenruo 写道:
> On 2022/11/11 17:02, 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 delaying the limit item updates until unlock the spin lock.
>
> The overall idea is way better now.
>
> But sorry that I didn't immediately find out the best solution at the 
> first glance.
>
> In fact, your v2 path just lets me remember what is the correct way to 
> handle such situation.
>
> > Signed-off-by: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>
> > ---
> >   fs/btrfs/qgroup.c | 18 +++++++++---------
> >   1 file changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> > index 9334c3157c22..2792d63c0da4 100644
> > --- a/fs/btrfs/qgroup.c
> > +++ b/fs/btrfs/qgroup.c
> [...]
> > @@ -2985,6 +2978,7 @@ int btrfs_qgroup_inherit(struct 
> > btrfs_trans_handle *trans, u64 srcid,
> >           dstgroup->max_excl = srcgroup->max_excl;
> >           dstgroup->rsv_rfer = srcgroup->rsv_rfer;
> >           dstgroup->rsv_excl = srcgroup->rsv_excl;
> > +        update_limit = true;
> >           qgroup_dirty(fs_info, dstgroup);
> >           qgroup_dirty(fs_info, srcgroup);
>
> You caught the "if (srcid)" branch, which also changed the 
> limit/rfer/excl numbers of the destination qgroup, but didn't call 
> update_qgroup_limit_item().
>
>
> But if you check the function qgroup_dirty() a little deeper, you can 
> find out that, qgroup_dirty() will move the target qgroup into 
> fs_info->dirty_qgroups list.
>
> And later at btrfs_run_qgroups() (which is called during 
> btrfs_commit_transaction(), and also after create_pending_snapshots()), 
> we will update the quota tree to reflect the result.
>
> So this means, all you need is just call qgroup_dirty() on @dstqgroup, 
> and call it a day.
> Everything else will be properly handled.
>
> Sorry I didn't notice this earlier...
>
> Thanks,
> Qu
>
> > @@ -3053,6 +3047,12 @@ int btrfs_qgroup_inherit(struct 
> > btrfs_trans_handle *trans, u64 srcid,
> >   unlock:
> >       spin_unlock(&fs_info->qgroup_lock);
> > +    if (update_limit && update_qgroup_limit_item(trans, dstgroup)) {
> > +        qgroup_mark_inconsistent(fs_info);
> > +        btrfs_info(fs_info,
> > +               "unable to update quota limit for %llu",
> > +               dstgroup->qgroupid);
> > +    }
> >       if (!ret)
> >           ret = btrfs_sysfs_add_one_qgroup(fs_info, dstgroup);
> >   out:
>
> .