Re: [PATCH 4.19 5.4 5.10 5.15 6.1 6.6 6.7] nilfs2: fix potential bug in end_buffer_async_write

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Feb 21, 2024 at 06:29:28AM +0900, Ryusuke Konishi wrote:
> commit 5bc09b397cbf1221f8a8aacb1152650c9195b02b upstream.
> 
> According to a syzbot report, end_buffer_async_write(), which handles the
> completion of block device writes, may detect abnormal condition of the
> buffer async_write flag and cause a BUG_ON failure when using nilfs2.
> 
> Nilfs2 itself does not use end_buffer_async_write().  But, the async_write
> flag is now used as a marker by commit 7f42ec394156 ("nilfs2: fix issue
> with race condition of competition between segments for dirty blocks") as
> a means of resolving double list insertion of dirty blocks in
> nilfs_lookup_dirty_data_buffers() and nilfs_lookup_node_buffers() and the
> resulting crash.
> 
> This modification is safe as long as it is used for file data and b-tree
> node blocks where the page caches are independent.  However, it was
> irrelevant and redundant to also introduce async_write for segment summary
> and super root blocks that share buffers with the backing device.  This
> led to the possibility that the BUG_ON check in end_buffer_async_write
> would fail as described above, if independent writebacks of the backing
> device occurred in parallel.
> 
> The use of async_write for segment summary buffers has already been
> removed in a previous change.
> 
> Fix this issue by removing the manipulation of the async_write flag for
> the remaining super root block buffer.
> 
> Link: https://lkml.kernel.org/r/20240203161645.4992-1-konishi.ryusuke@gmail.com
> Fixes: 7f42ec394156 ("nilfs2: fix issue with race condition of competition between segments for dirty blocks")
> Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
> Reported-by: syzbot+5c04210f7c7f897c1e7f@syzkaller.appspotmail.com
> Closes: https://lkml.kernel.org/r/00000000000019a97c05fd42f8c8@google.com
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Now queued up, thanks.

greg k-h