Re: [f2fs-dev] [PATCH V2] f2fs: Avoid double lock for cp_rwsem during checkpoint

Re: [f2fs-dev] [PATCH V2] f2fs: Avoid double lock for cp_rwsem during checkpoint

[Markus Elfring]

> … This results in deadlock as
> iput() tries to hold cp_rwsem, which is already held at the
> beginning by checkpoint->block_operations().

Will another imperative wording become helpful besides the provided information
for this change description?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?id=6a8b55ed4056ea5559ebe4f6a4b247f627870d4c#n151

Would you like to add the tag “Fixes” because of adjustments
for the data synchronisation?

Regards,
Markus


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Re: [f2fs-dev] [PATCH V2] f2fs: Avoid double lock for cp_rwsem during checkpoint

[Sayali Lokhande]

Hi Markus

On 4/27/2020 4:08 PM, Markus Elfring wrote:
>> … This results in deadlock as
>> iput() tries to hold cp_rwsem, which is already held at the
>> beginning by checkpoint->block_operations().
> Will another imperative wording become helpful besides the provided information
> for this change description?
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?id=6a8b55ed4056ea5559ebe4f6a4b247f627870d4c#n151
>
> Would you like to add the tag “Fixes” because of adjustments
> for the data synchronisation?

I couldn't find any past commit which suits to be added under "Fixes" 
here. Let me know if you have any other comment.

>
> Regards,
> Markus


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Re: [f2fs-dev] [PATCH V2] f2fs: Avoid double lock for cp_rwsem during checkpoint

[Dan Carpenter]

On Wed, Apr 29, 2020 at 10:28:36AM +0530, Sayali Lokhande wrote:
> Hi Markus
> 
> On 4/27/2020 4:08 PM, Markus Elfring wrote:
> > > … This results in deadlock as
> > > iput() tries to hold cp_rwsem, which is already held at the
> > > beginning by checkpoint->block_operations().
> > Will another imperative wording become helpful besides the provided information
> > for this change description?
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?id=6a8b55ed4056ea5559ebe4f6a4b247f627870d4c#n151
> > 
> > Would you like to add the tag “Fixes” because of adjustments
> > for the data synchronisation?
> 
> I couldn't find any past commit which suits to be added under "Fixes" here.
> Let me know if you have any other comment.

This looks really old.  Maybe commit 399368372ed9 ("f2fs: introduce a
new global lock scheme")?

regards,
dan carpenter



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Re: [f2fs-dev] [PATCH V2] f2fs: Avoid double lock for cp_rwsem during checkpoint

[Sayali Lokhande]

On 4/29/2020 6:14 PM, Dan Carpenter wrote:
> On Wed, Apr 29, 2020 at 10:28:36AM +0530, Sayali Lokhande wrote:
>> Hi Markus
>>
>> On 4/27/2020 4:08 PM, Markus Elfring wrote:
>>>> … This results in deadlock as
>>>> iput() tries to hold cp_rwsem, which is already held at the
>>>> beginning by checkpoint->block_operations().
>>> Will another imperative wording become helpful besides the provided information
>>> for this change description?
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?id=6a8b55ed4056ea5559ebe4f6a4b247f627870d4c#n151
>>>
>>> Would you like to add the tag “Fixes” because of adjustments
>>> for the data synchronisation?
>> I couldn't find any past commit which suits to be added under "Fixes" here.
>> Let me know if you have any other comment.
> This looks really old.  Maybe commit 399368372ed9 ("f2fs: introduce a
> new global lock scheme")?
Yes. Let me update it in Fixes tag in V3 and post it. Thanks for 
pointing it.
>
> regards,
> dan carpenter
>


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[f2fs-dev] [PATCH V2] f2fs: Avoid double lock for cp_rwsem during checkpoint

[Sayali Lokhande]

There could be a scenario where f2fs_sync_node_pages gets
called during checkpoint, which in turn tries to flush
inline data and calls iput(). This results in deadlock as
iput() tries to hold cp_rwsem, which is already held at the
beginning by checkpoint->block_operations().

Call stack :

Thread A		Thread B
f2fs_write_checkpoint()
- block_operations(sbi)
 - f2fs_lock_all(sbi);
  - down_write(&sbi->cp_rwsem);

                        - open()
                         - igrab()
                        - write() write inline data
                        - unlink()
- f2fs_sync_node_pages()
 - if (is_inline_node(page))
  - flush_inline_data()
   - ilookup()
     page = f2fs_pagecache_get_page()
     if (!page)
      goto iput_out;
     iput_out:

    - iput()
       iput(inode);
       - f2fs_evict_inode()
        - f2fs_truncate_blocks()
         - f2fs_lock_op()
           - down_read(&sbi->cp_rwsem);

Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>
---
 fs/f2fs/checkpoint.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 5ba649e..97b6378 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1219,21 +1219,19 @@ static int block_operations(struct f2fs_sb_info *sbi)
 		goto retry_flush_quotas;
 	}
 
-retry_flush_nodes:
 	down_write(&sbi->node_write);
 
 	if (get_pages(sbi, F2FS_DIRTY_NODES)) {
 		up_write(&sbi->node_write);
+		up_write(&sbi->node_change);
+		f2fs_unlock_all(sbi);
 		atomic_inc(&sbi->wb_sync_req[NODE]);
 		err = f2fs_sync_node_pages(sbi, &wbc, false, FS_CP_NODE_IO);
 		atomic_dec(&sbi->wb_sync_req[NODE]);
-		if (err) {
-			up_write(&sbi->node_change);
-			f2fs_unlock_all(sbi);
+		if (err)
 			goto out;
-		}
 		cond_resched();
-		goto retry_flush_nodes;
+		goto retry_flush_quotas;
 	}
 
 	/*
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project


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Re: [f2fs-dev] [PATCH V2] f2fs: Avoid double lock for cp_rwsem during checkpoint

[Chao Yu]

On 2020/4/27 14:00, Sayali Lokhande wrote:
> There could be a scenario where f2fs_sync_node_pages gets
> called during checkpoint, which in turn tries to flush
> inline data and calls iput(). This results in deadlock as
> iput() tries to hold cp_rwsem, which is already held at the
> beginning by checkpoint->block_operations().
> 
> Call stack :
> 
> Thread A		Thread B
> f2fs_write_checkpoint()
> - block_operations(sbi)
>  - f2fs_lock_all(sbi);
>   - down_write(&sbi->cp_rwsem);
> 
>                         - open()
>                          - igrab()
>                         - write() write inline data
>                         - unlink()
> - f2fs_sync_node_pages()
>  - if (is_inline_node(page))
>   - flush_inline_data()
>    - ilookup()
>      page = f2fs_pagecache_get_page()
>      if (!page)
>       goto iput_out;
>      iput_out:
> 
>     - iput()
        ^^^^
			 - close()
			 - iput()

>        iput(inode);
>        - f2fs_evict_inode()
>         - f2fs_truncate_blocks()
>          - f2fs_lock_op()
>            - down_read(&sbi->cp_rwsem);
> 
> Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>

Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks,


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