Hi Greg,
On 2019/3/7 20:25, Greg KH wrote:
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@vger.kernel.org # 4.19+ Signed-off-by: Gao Xiang gaoxiang25@huawei.com Reviewed-by: Chao Yu yuchao0@huawei.com
drivers/staging/erofs/unzip_vle.c | 69 +++++++++++++++++++++++++-------------- 1 file changed, 44 insertions(+), 25 deletions(-)
thanks for the backport, now applied.
Yes, it seems that Sasha's bot cannot cherry-pick it directly, therefore I made this patch for 4.19 by hand...
BTW, there is another patch called "staging: erofs: compressed_pages should not be accessed again after freed" in the same condition... And I also send 4.19 and 4.20 version to stable mailing list, could you also kindly check them out?
Thanks, Gao Xiang
greg k-h