[PATCH] f2fs: Fix deadlock in shutdown ioctl

[PATCH] f2fs: Fix deadlock in shutdown ioctl

[Sahitya Tummala]

f2fs_ioc_shutdown() ioctl gets stuck in the below path
when going down with full sync (F2FS_GOING_DOWN_FULLSYNC)
option.

__switch_to+0x90/0xc4
percpu_down_write+0x8c/0xc0
freeze_super+0xec/0x1e4
freeze_bdev+0xc4/0xcc
f2fs_ioctl+0xc0c/0x1ce0
f2fs_compat_ioctl+0x98/0x1f0

Fix this by not holding write access during this ioctl.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
---
 fs/f2fs/file.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index b926df7..2c2e61b 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1835,10 +1835,6 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
 	if (get_user(in, (__u32 __user *)arg))
 		return -EFAULT;
 
-	ret = mnt_want_write_file(filp);
-	if (ret)
-		return ret;
-
 	switch (in) {
 	case F2FS_GOING_DOWN_FULLSYNC:
 		sb = freeze_bdev(sb->s_bdev);
@@ -1878,7 +1874,6 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
 
 	f2fs_update_time(sbi, REQ_TIME);
 out:
-	mnt_drop_write_file(filp);
 	return ret;
 }
 
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.

Re: [PATCH] f2fs: Fix deadlock in shutdown ioctl

[Chao Yu]

On 2018/5/10 21:20, Sahitya Tummala wrote:
> f2fs_ioc_shutdown() ioctl gets stuck in the below path
> when going down with full sync (F2FS_GOING_DOWN_FULLSYNC)
> option.
> 
> __switch_to+0x90/0xc4
> percpu_down_write+0x8c/0xc0
> freeze_super+0xec/0x1e4
> freeze_bdev+0xc4/0xcc
> f2fs_ioctl+0xc0c/0x1ce0
> f2fs_compat_ioctl+0x98/0x1f0
> 
> Fix this by not holding write access during this ioctl.

I think we can just remove lock coverage for F2FS_GOING_DOWN_FULLSYNC path, for
other path, we need to keep as it is.

Thanks,

> 
> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
> ---
>  fs/f2fs/file.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index b926df7..2c2e61b 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1835,10 +1835,6 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
>  	if (get_user(in, (__u32 __user *)arg))
>  		return -EFAULT;
>  
> -	ret = mnt_want_write_file(filp);
> -	if (ret)
> -		return ret;
> -
>  	switch (in) {
>  	case F2FS_GOING_DOWN_FULLSYNC:
>  		sb = freeze_bdev(sb->s_bdev);
> @@ -1878,7 +1874,6 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
>  
>  	f2fs_update_time(sbi, REQ_TIME);
>  out:
> -	mnt_drop_write_file(filp);
>  	return ret;
>  }
>  
> 

Re: [PATCH] f2fs: Fix deadlock in shutdown ioctl

[Sahitya Tummala]

On Mon, May 14, 2018 at 11:39:42AM +0800, Chao Yu wrote:
> On 2018/5/10 21:20, Sahitya Tummala wrote:
> > f2fs_ioc_shutdown() ioctl gets stuck in the below path
> > when going down with full sync (F2FS_GOING_DOWN_FULLSYNC)
> > option.
> > 
> > __switch_to+0x90/0xc4
> > percpu_down_write+0x8c/0xc0
> > freeze_super+0xec/0x1e4
> > freeze_bdev+0xc4/0xcc
> > f2fs_ioctl+0xc0c/0x1ce0
> > f2fs_compat_ioctl+0x98/0x1f0
> > 
> > Fix this by not holding write access during this ioctl.
> 
> I think we can just remove lock coverage for F2FS_GOING_DOWN_FULLSYNC path, for
> other path, we need to keep as it is.
>

Thanks, I thought about it too but then I checked that XFS shutdown ioctl is
not taking any lock for this ioctl. Hence, I followed the same in F2FS.
Do you know why XFS is not taking any lock? Is it really needed in shutdown
ioctl?

--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

Re: [PATCH] f2fs: Fix deadlock in shutdown ioctl

[Chao Yu]

On 2018/5/15 15:57, Sahitya Tummala wrote:
> On Mon, May 14, 2018 at 11:39:42AM +0800, Chao Yu wrote:
>> On 2018/5/10 21:20, Sahitya Tummala wrote:
>>> f2fs_ioc_shutdown() ioctl gets stuck in the below path
>>> when going down with full sync (F2FS_GOING_DOWN_FULLSYNC)
>>> option.
>>>
>>> __switch_to+0x90/0xc4
>>> percpu_down_write+0x8c/0xc0
>>> freeze_super+0xec/0x1e4
>>> freeze_bdev+0xc4/0xcc
>>> f2fs_ioctl+0xc0c/0x1ce0
>>> f2fs_compat_ioctl+0x98/0x1f0
>>>
>>> Fix this by not holding write access during this ioctl.
>>
>> I think we can just remove lock coverage for F2FS_GOING_DOWN_FULLSYNC path, for
>> other path, we need to keep as it is.
>>
> 
> Thanks, I thought about it too but then I checked that XFS shutdown ioctl is
> not taking any lock for this ioctl. Hence, I followed the same in F2FS.
> Do you know why XFS is not taking any lock? 

I don't know. :(

> Is it really needed in shutdown ioctl?

IMO, yes, we should keep freeze and remount be aware of the shutdown operation.

Thanks,

> 
> --
> Sent by a consultant of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
> 
> 

Re: [PATCH] f2fs: Fix deadlock in shutdown ioctl

[Sahitya Tummala]

On Wed, May 16, 2018 at 02:48:42PM +0800, Chao Yu wrote:
> > 
> > Thanks, I thought about it too but then I checked that XFS shutdown ioctl is
> > not taking any lock for this ioctl. Hence, I followed the same in F2FS.
> > Do you know why XFS is not taking any lock? 
> 
> I don't know. :(

No problem :)

> 
> > Is it really needed in shutdown ioctl?
> 
> IMO, yes, we should keep freeze and remount be aware of the shutdown operation.

Thanks for your inputs. I will send the updated patch set.

--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.