| Message ID | 20210116071533.105780-8-wqu@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | btrfs: add read-only support for subpage sector size | expand |
On 1/16/21 2:15 AM, Qu Wenruo wrote: > Even for regular btrfs, there are locations where we allocate dummy > extent buffers for temporary usage. > > Like tree_mod_log_rewind() and get_old_root(). > > Those dummy extent buffers will be handled by the same eb accessors, and > if they don't have page::private subpage eb accessors can fail. > > To address such problems, make __alloc_dummy_extent_buffer() to attach > page private for dummy extent buffers too. > > Signed-off-by: Qu Wenruo <wqu@suse.com> We already know these eb's are fake because they have UNMAPPED set, just adjust your subpage helpers to be no-op if UNMAPPED is set. Thanks, Josef
On 2021/1/20 下午10:48, Josef Bacik wrote: > On 1/16/21 2:15 AM, Qu Wenruo wrote: >> Even for regular btrfs, there are locations where we allocate dummy >> extent buffers for temporary usage. >> >> Like tree_mod_log_rewind() and get_old_root(). >> >> Those dummy extent buffers will be handled by the same eb accessors, and >> if they don't have page::private subpage eb accessors can fail. >> >> To address such problems, make __alloc_dummy_extent_buffer() to attach >> page private for dummy extent buffers too. >> >> Signed-off-by: Qu Wenruo <wqu@suse.com> > > We already know these eb's are fake because they have UNMAPPED set, just > adjust your subpage helpers to be no-op if UNMAPPED is set. Thanks, But then the helper behavior would be a mess. Some accessors, like read/write_extent_buffer() will still do subpage specific offset calcuation, even it has UNMAPPED bit. Thus I still prefer to do the same operations, reducing the branches in accessors. Thanks, Qu > > Josef
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index fb800f237099..7f94f00936d7 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -5204,9 +5204,14 @@ struct extent_buffer *__alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info, num_pages = num_extent_pages(eb); for (i = 0; i < num_pages; i++) { + int ret; + eb->pages[i] = alloc_page(GFP_NOFS); if (!eb->pages[i]) goto err; + ret = attach_extent_buffer_page(eb, eb->pages[i], NULL); + if (ret < 0) + goto err; } set_extent_buffer_uptodate(eb); btrfs_set_header_nritems(eb, 0); @@ -5214,8 +5219,10 @@ struct extent_buffer *__alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info, return eb; err: - for (; i > 0; i--) + for (; i > 0; i--) { + detach_extent_buffer_page(eb, eb->pages[i - 1]); __free_page(eb->pages[i - 1]); + } __free_extent_buffer(eb); return NULL; }
Even for regular btrfs, there are locations where we allocate dummy extent buffers for temporary usage. Like tree_mod_log_rewind() and get_old_root(). Those dummy extent buffers will be handled by the same eb accessors, and if they don't have page::private subpage eb accessors can fail. To address such problems, make __alloc_dummy_extent_buffer() to attach page private for dummy extent buffers too. Signed-off-by: Qu Wenruo <wqu@suse.com> --- fs/btrfs/extent_io.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)