On Thu, Mar 07, 2019 at 01:34:04PM +0800, Gao Xiang wrote:
> commit a112152f6f3a2a88caa6f414d540bd49e406af60 upstream.
>
> EROFS has an optimized path called TAIL merging, which is designed
> to merge multiple reads and the corresponding decompressions into
> one if these requests read continuous pages almost at the same time.
>
> In general, it behaves as follows:
> ________________________________________________________________
> ... | TAIL . HEAD | PAGE | PAGE | TAIL . HEAD | ...
> _____|_combined page A_|________|________|_combined page B_|____
> 1 ] -> [ 2 ] -> [ 3
> If the above three reads are requested in the order 1-2-3, it will
> generate a large work chain rather than 3 individual work chains
> to reduce scheduling overhead and boost up sequential read.
>
> However, if Read 2 is processed slightly earlier than Read 1,
> currently it still generates 2 individual work chains (chain 1, 2)
> but it does in-place decompression for combined page A, moreover,
> if chain 2 decompresses ahead of chain 1, it will be a race and
> lead to corrupted decompressed page. This patch fixes it.
>
> Fixes: 3883a79abd02 ("staging: erofs: introduce VLE decompression support")
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.19+
> Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
> Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
> ---
> drivers/staging/erofs/unzip_vle.c | 69 +++++++++++++++++++++++++--------------
> 1 file changed, 44 insertions(+), 25 deletions(-)
>
thanks for the backport, now applied.
greg k-h
