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SubjectRe: [PATCH v2] f2fs: fix to keep isolation of atomic write
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On 2021/1/15 5:53, Jaegeuk Kim wrote:
> On 12/30, Chao Yu wrote:
>> ThreadA ThreadB
>> - f2fs_ioc_start_atomic_write
>> - write
>> - f2fs_ioc_commit_atomic_write
>> - f2fs_commit_inmem_pages
>> - f2fs_drop_inmem_pages
>> - f2fs_drop_inmem_pages
>> - __revoke_inmem_pages
>> - f2fs_vm_page_mkwrite
>> - set_page_dirty
>> - tag ATOMIC_WRITTEN_PAGE and add page
>> to inmem_pages list
>> - clear_inode_flag(FI_ATOMIC_FILE)
>> - f2fs_vm_page_mkwrite
>> - set_page_dirty
>> - f2fs_update_dirty_page
>> - f2fs_trace_pid
>> - tag inmem page private to pid
>
> Hmm, how about removing fs/f2fs/trace.c to make private more complicated
> like this? I think we can get IO traces from tracepoints.

Hmm, actually, there is are issues, one is the trace IO, the other is the
race issue (atomic_start,commit,drop vs mkwrite) which can make isolation
semantics of transaction be broken.

Or can we avoid atomic file racing with file mmap?

- atomic_start - file_mmap
- inode_lock
- if (FI_ATOMIC_FILE) return
- inode_lock
- if (FI_MMAP_FILE) return

Thanks,

>
>> - truncate
>> - f2fs_invalidate_page
>> - set page->mapping to NULL
>> then it will cause panic once we
>> access page->mapping
>>
>> The root cause is we missed to keep isolation of atomic write in the case
>> of commit_atomic_write vs mkwrite, let commit_atomic_write helds i_mmap_sem
>> lock to avoid this issue.
>>
>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>> ---
>> v2:
>> - use i_mmap_sem to avoid mkwrite racing with below flows:
>> * f2fs_ioc_start_atomic_write
>> * f2fs_drop_inmem_pages
>> * f2fs_commit_inmem_pages
>>
>> fs/f2fs/file.c | 3 +++
>> fs/f2fs/segment.c | 7 +++++++
>> 2 files changed, 10 insertions(+)
>>
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index 4e6d4b9120a8..a48ec650d691 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -2050,6 +2050,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>> goto out;
>>
>> down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>> + down_write(&F2FS_I(inode)->i_mmap_sem);
>>
>> /*
>> * Should wait end_io to count F2FS_WB_CP_DATA correctly by
>> @@ -2060,6 +2061,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>> inode->i_ino, get_dirty_pages(inode));
>> ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
>> if (ret) {
>> + up_write(&F2FS_I(inode)->i_mmap_sem);
>> up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>> goto out;
>> }
>> @@ -2073,6 +2075,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>> /* add inode in inmem_list first and set atomic_file */
>> set_inode_flag(inode, FI_ATOMIC_FILE);
>> clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
>> + up_write(&F2FS_I(inode)->i_mmap_sem);
>> up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>
>> f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index d8570b0359f5..dab870d9faf6 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -327,6 +327,8 @@ void f2fs_drop_inmem_pages(struct inode *inode)
>> struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>> struct f2fs_inode_info *fi = F2FS_I(inode);
>>
>> + down_write(&F2FS_I(inode)->i_mmap_sem);
>> +
>> while (!list_empty(&fi->inmem_pages)) {
>> mutex_lock(&fi->inmem_lock);
>> __revoke_inmem_pages(inode, &fi->inmem_pages,
>> @@ -344,6 +346,8 @@ void f2fs_drop_inmem_pages(struct inode *inode)
>> sbi->atomic_files--;
>> }
>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>> +
>> + up_write(&F2FS_I(inode)->i_mmap_sem);
>> }
>>
>> void f2fs_drop_inmem_page(struct inode *inode, struct page *page)
>> @@ -467,6 +471,7 @@ int f2fs_commit_inmem_pages(struct inode *inode)
>> f2fs_balance_fs(sbi, true);
>>
>> down_write(&fi->i_gc_rwsem[WRITE]);
>> + down_write(&F2FS_I(inode)->i_mmap_sem);
>>
>> f2fs_lock_op(sbi);
>> set_inode_flag(inode, FI_ATOMIC_COMMIT);
>> @@ -478,6 +483,8 @@ int f2fs_commit_inmem_pages(struct inode *inode)
>> clear_inode_flag(inode, FI_ATOMIC_COMMIT);
>>
>> f2fs_unlock_op(sbi);
>> +
>> + up_write(&F2FS_I(inode)->i_mmap_sem);
>> up_write(&fi->i_gc_rwsem[WRITE]);
>>
>> return err;
>> --
>> 2.29.2
> .
>

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