From mboxrd@z Thu Jan 1 00:00:00 1970 From: greg@kroah.com (Greg KH) Date: Thu, 7 Mar 2019 16:21:47 +0100 Subject: [PATCH for-4.19] staging: erofs: fix mis-acted TAIL merging behavior In-Reply-To: <5b7e1914-f8e5-da3d-4492-17d6afc00fb1@huawei.com> References: <20190301212203.5FE0C2084F@mail.kernel.org> <20190307053404.29108-1-gaoxiang25@huawei.com> <20190307122539.GD21325@kroah.com> <5b7e1914-f8e5-da3d-4492-17d6afc00fb1@huawei.com> Message-ID: <20190307152147.GA24453@kroah.com> On Thu, Mar 07, 2019@09:04:06PM +0800, Gao Xiang wrote: > Hi Greg, > > On 2019/3/7 20:25, Greg KH wrote: > > On Thu, Mar 07, 2019@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: # 4.19+ > >> Signed-off-by: Gao Xiang > >> Reviewed-by: Chao Yu > >> --- > >> 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? Yes, please give me a chance to catch up on stable pending patches to process: $ mdfrm -c ~/mail/stable/ 585 messages in /home/gregkh/mail/stable/ You are in good company :) greg k-h