Re: [PATCH v3] f2fs: fix to keep isolation of atomic write

Jaegeuk Kim
2021-04-13T17:46:12Z

On 04/13, Chao Yu wrote:
> On 2021/4/13 11:27, Jaegeuk Kim wrote:
> > On 04/12, Chao Yu wrote:
> > > As Yi Chen reported, there is a potential race case described as below:
> > >
> > > Thread A Thread B
> > > - f2fs_ioc_start_atomic_write
> > > - mkwrite
> > > - set_page_dirty
> > > - f2fs_set_page_private(page, 0)
> > > - set_inode_flag(FI_ATOMIC_FILE)
> > > - mkwrite same page
> > > - set_page_dirty
> > > - f2fs_register_inmem_page
> > > - f2fs_set_page_private(ATOMIC_WRITTEN_PAGE)
> > > failed due to PagePrivate flag has been set
> > > - list_add_tail
> > > - truncate_inode_pages
> > > - f2fs_invalidate_page
> > > - clear page private but w/o remove it from
> > > inmem_list
> > > - set page->mapping to NULL
> > > - f2fs_ioc_commit_atomic_write
> > > - __f2fs_commit_inmem_pages
> > > - __revoke_inmem_pages
> > > - f2fs_put_page panic as page->mapping is NULL
> > >
> > > The root cause is we missed to keep isolation of atomic write in the case
> > > of start_atomic_write vs mkwrite, let start_atomic_write helds i_mmap_sem
> > > lock to avoid this issue.
> >
> > My only concern is performance regression. Could you please verify the numbers?
>
> Do you have specific test script?
>
> IIRC, the scenario you mean is multi-threads write/mmap the same db, right?

I suggest to run sqlite transaction/check operations in android devices in parallel.

>
> Thanks,
>
> >
> > >
> > > Reported-by: Yi Chen <chenyi77@huawei.com>
> > > Signed-off-by: Chao Yu <yuchao0@huawei.com>
> > > ---
> > > v3:
> > > - rebase to last dev branch
> > > - update commit message because this patch fixes a different racing issue
> > > of atomic write
> > > fs/f2fs/file.c | 3 +++
> > > fs/f2fs/segment.c | 6 ++++++
> > > 2 files changed, 9 insertions(+)
> > >
> > > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > > index d697c8900fa7..6284b2f4a60b 100644
> > > --- a/fs/f2fs/file.c
> > > +++ b/fs/f2fs/file.c
> > > @@ -2054,6 +2054,7 @@ 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
> > > @@ -2064,6 +2065,7 @@ 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;
> > > }
> > > @@ -2077,6 +2079,7 @@ 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 0cb1ca88d4aa..78c8342f52fd 100644
> > > --- a/fs/f2fs/segment.c
> > > +++ b/fs/f2fs/segment.c
> > > @@ -325,6 +325,7 @@ void f2fs_drop_inmem_pages(struct inode *inode)
> > > struct f2fs_inode_info *fi = F2FS_I(inode);
> > > do {
> > > + down_write(&F2FS_I(inode)->i_mmap_sem);
> > > mutex_lock(&fi->inmem_lock);
> > > if (list_empty(&fi->inmem_pages)) {
> > > fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> > > @@ -339,11 +340,13 @@ void f2fs_drop_inmem_pages(struct inode *inode)
> > > spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> > > mutex_unlock(&fi->inmem_lock);
> > > + up_write(&F2FS_I(inode)->i_mmap_sem);
> > > break;
> > > }
> > > __revoke_inmem_pages(inode, &fi->inmem_pages,
> > > true, false, true);
> > > mutex_unlock(&fi->inmem_lock);
> > > + up_write(&F2FS_I(inode)->i_mmap_sem);
> > > } while (1);
> > > }
> > > @@ -468,6 +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);
> > > @@ -479,6 +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
> > .
> >