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

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

[ChenXiaoSong]

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.

Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
---
 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
@@ -2860,6 +2860,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
 	bool need_rescan = false;
 	u32 level_size = 0;
 	u64 nums;
+	bool update_limit = false;
 
 	/*
 	 * There are only two callers of this function.
@@ -2950,15 +2951,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
 		dstgroup->max_excl = inherit->lim.max_excl;
 		dstgroup->rsv_rfer = inherit->lim.rsv_rfer;
 		dstgroup->rsv_excl = inherit->lim.rsv_excl;
-
-		ret = update_qgroup_limit_item(trans, dstgroup);
-		if (ret) {
-			qgroup_mark_inconsistent(fs_info);
-			btrfs_info(fs_info,
-				   "unable to update quota limit for %llu",
-				   dstgroup->qgroupid);
-			goto unlock;
-		}
+		update_limit = true;
 	}
 
 	if (srcid) {
@@ -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);
@@ -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:
-- 
2.31.1

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

[Qu Wenruo]

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@huawei.com>
> ---
>   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:

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@huawei.com>
>> ---
>>   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:
> 
> .