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    SubjectRe: [PATCH v2] f2fs: fix to keep isolation of atomic write
    On 01/15, Chao Yu wrote:
    > 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?

    No, we can't. We may need to find other way to check the race. :)

    >
    > - 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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