2019-12-06 03:33:27

by Chao Yu

Subject: [PATCH] f2fs: fix to relocate f2fs_balance_fs() in mkwrite()

As Dinosaur Huang reported, there is a potential deadlock in between
GC and mkwrite():

Thread A Thread B
- do_page_mkwrite
- f2fs_vm_page_mkwrite
- lock_page
- f2fs_balance_fs
- mutex_lock(gc_mutex)
- f2fs_gc
- do_garbage_collect
- ra_data_block
- grab_cache_page
- f2fs_balance_fs
- mutex_lock(gc_mutex)

In order to fix this, we just move f2fs_balance_fs() out of page lock's
coverage in f2fs_vm_page_mkwrite().

Reported-by: Dinosaur Huang <[email protected]>
Signed-off-by: Chao Yu <[email protected]>
---
fs/f2fs/file.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index c0560d62dbee..ed3290225506 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -67,6 +67,8 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)

f2fs_bug_on(sbi, f2fs_has_inline_data(inode));

+ f2fs_balance_fs(sbi, true);
+
file_update_time(vmf->vma->vm_file);
down_read(&F2FS_I(inode)->i_mmap_sem);
lock_page(page);
@@ -120,8 +122,6 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
out_sem:
up_read(&F2FS_I(inode)->i_mmap_sem);

- f2fs_balance_fs(sbi, dn.node_changed);
-
sb_end_pagefault(inode->i_sb);
err:
return block_page_mkwrite_return(err);
--
2.18.0.rc1

2019-12-06 04:09:28

by Jaegeuk Kim

Subject: Re: [PATCH] f2fs: fix to relocate f2fs_balance_fs() in mkwrite()

Hi Chao,

I was testing this.

https://github.com/jaegeuk/f2fs/commit/76be33b9f1fce70dd2d3f04f66d0f78b418fe3f5

On 12/06, Chao Yu wrote:
> As Dinosaur Huang reported, there is a potential deadlock in between
> GC and mkwrite():
>
> Thread A Thread B
> - do_page_mkwrite
> - f2fs_vm_page_mkwrite
> - lock_page
> - f2fs_balance_fs
> - mutex_lock(gc_mutex)
> - f2fs_gc
> - do_garbage_collect
> - ra_data_block
> - grab_cache_page
> - f2fs_balance_fs
> - mutex_lock(gc_mutex)
>
> In order to fix this, we just move f2fs_balance_fs() out of page lock's
> coverage in f2fs_vm_page_mkwrite().
>
> Reported-by: Dinosaur Huang <[email protected]>
> Signed-off-by: Chao Yu <[email protected]>
> ---
> fs/f2fs/file.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index c0560d62dbee..ed3290225506 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -67,6 +67,8 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>
> f2fs_bug_on(sbi, f2fs_has_inline_data(inode));
>
> + f2fs_balance_fs(sbi, true);
> +
> file_update_time(vmf->vma->vm_file);
> down_read(&F2FS_I(inode)->i_mmap_sem);
> lock_page(page);
> @@ -120,8 +122,6 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
> out_sem:
> up_read(&F2FS_I(inode)->i_mmap_sem);
>
> - f2fs_balance_fs(sbi, dn.node_changed);
> -
> sb_end_pagefault(inode->i_sb);
> err:
> return block_page_mkwrite_return(err);
> --
> 2.18.0.rc1

2019-12-06 04:33:23

by Chao Yu

Subject: Re: [PATCH] f2fs: fix to relocate f2fs_balance_fs() in mkwrite()

Hi Jaeguek,

On 2019/12/6 12:08, Jaegeuk Kim wrote:
> Hi Chao,
>
> I was testing this.
>
> https://github.com/jaegeuk/f2fs/commit/76be33b9f1fce70dd2d3f04f66d0f78b418fe3f5

The patch looks good.

BTW, do you mind adding below call stack into your patch? I guess it
describes this ABBA deadlock with more details. :)

Thanks,

>
> On 12/06, Chao Yu wrote:
>> As Dinosaur Huang reported, there is a potential deadlock in between
>> GC and mkwrite():
>>
>> Thread A Thread B
>> - do_page_mkwrite
>> - f2fs_vm_page_mkwrite
>> - lock_page
>> - f2fs_balance_fs
>> - mutex_lock(gc_mutex)
>> - f2fs_gc
>> - do_garbage_collect
>> - ra_data_block
>> - grab_cache_page
>> - f2fs_balance_fs
>> - mutex_lock(gc_mutex)
>>
>> In order to fix this, we just move f2fs_balance_fs() out of page lock's
>> coverage in f2fs_vm_page_mkwrite().
>>
>> Reported-by: Dinosaur Huang <[email protected]>
>> Signed-off-by: Chao Yu <[email protected]>
>> ---
>> fs/f2fs/file.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index c0560d62dbee..ed3290225506 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -67,6 +67,8 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>>
>> f2fs_bug_on(sbi, f2fs_has_inline_data(inode));
>>
>> + f2fs_balance_fs(sbi, true);
>> +
>> file_update_time(vmf->vma->vm_file);
>> down_read(&F2FS_I(inode)->i_mmap_sem);
>> lock_page(page);
>> @@ -120,8 +122,6 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>> out_sem:
>> up_read(&F2FS_I(inode)->i_mmap_sem);
>>
>> - f2fs_balance_fs(sbi, dn.node_changed);
>> -
>> sb_end_pagefault(inode->i_sb);
>> err:
>> return block_page_mkwrite_return(err);
>> --
>> 2.18.0.rc1
> .
>