This is needed for long term kernel 2.6.35.14. Please let me know for any changes/suggestions. Thanks & Regards, Amit Sahrawat xfs: serialise unaligned direct IOs This patch published in 2.6.38 kernel(Original reference http://oss.sgi.com/archives/xfs/2011-01/msg00013.html), but can not be applied to 2.6.35 kernel directly, because of the absence of required function, its reimplmented to resolve xfstest test 240 fail. When two concurrent unaligned, non-overlapping direct IOs are issued to the same block, the direct Io layer will race to zero the block. The result is that one of the concurrent IOs will overwrite data written by the other IO with zeros. This is demonstrated by the xfsqa test 240. To avoid this problem, serialise all unaligned direct IOs to an inode with a big hammer. We need a big hammer approach as we need to serialise AIO as well, so we can't just block writes on locks. Hence, the big hammer is calling xfs_ioend_wait() while holding out other unaligned direct IOs from starting. We don't bother trying to serialised aligned vs unaligned IOs as they are overlapping IO and the result of concurrent overlapping IOs is undefined - the result of either IO is a valid result so we let them race. Hence we only penalise unaligned IO, which already has a major overhead compared to aligned IO so this isn't a major problem. diff -Nurp linux-Orig/fs/xfs/linux-2.6/xfs_file.c linux-Updated/fs/xfs/linux-2.6/xfs_file.c --- linux-Orig/fs/xfs/linux-2.6/xfs_file.c 2011-10-28 12:10:52.000000000 +0530 +++ linux-Updated/fs/xfs/linux-2.6/xfs_file.c 2011-10-29 12:34:45.000000000 +0530 @@ -587,6 +587,7 @@ xfs_file_aio_write( xfs_fsize_t isize, new_size; int iolock; size_t ocount = 0, count; + int unaligned_io = 0; int need_i_mutex; XFS_STATS_INC(xs_write_calls); @@ -641,7 +642,10 @@ start: return XFS_ERROR(-EINVAL); } - if (!need_i_mutex && (mapping->nrpages || pos > ip->i_size)) { + if ((pos & mp->m_blockmask) || ((pos + count) & mp->m_blockmask)) + unaligned_io = 1; + + if (!need_i_mutex && ( unaligned_io || mapping->nrpages || pos > ip->i_size)) { xfs_iunlock(ip, XFS_ILOCK_EXCL|iolock); iolock = XFS_IOLOCK_EXCL; need_i_mutex = 1; @@ -700,11 +704,15 @@ start: } if (need_i_mutex) { - /* demote the lock now the cached pages are gone */ - xfs_ilock_demote(ip, XFS_IOLOCK_EXCL); + if (unaligned_io) + xfs_ioend_wait(ip); + /* demote the lock now the cached pages are gone if we can */ + else { + xfs_ilock_demote(ip, XFS_IOLOCK_EXCL); + iolock = XFS_IOLOCK_SHARED; + } mutex_unlock(&inode->i_mutex); - iolock = XFS_IOLOCK_SHARED; need_i_mutex = 0; } _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
