On Thu, Feb 22, 2018 at 12:24:40PM -0700, Liu Bo wrote: > > > > Not even that far, isize is truncated before calling inode_dio_wait() > > > > and a memory barrier is set to ensure the correct order, so dio read > > > > would simply return if it's reading past isize. > > > > > > Please, describe concretely which meory barriers pairs with chich in > > > order to ensure proper visibility. Because I'm of the opinion there are > > > insufficient memoru barriers to ensure setting READDIO_LOCK is properly > > > visible in btrfs_direct_IO. Since the latter has no barriers whatsoever. > > > > smp_mb() is supposed to be paired, so there is one missing, I agree. > > > > So the missing smp_mb() was there (commit > 2e60a51e62185cce48758e596ae7cb2da673b58f), but was removed in some > cleanup I guess. Not a cleanup, and not a single commit: 38851cc19adbfa1def2b47106d8050a80e0a3673 Btrfs: serialize unlocked dio reads with truncate Signed-off-by: Miao Xie <miaox@xxxxxxxxxxxxxx> at this time the i_dio_counter was still used directly and the barrier was moved before the if-else block, technically still in the right before the test_bit. dc59215d4f42084ee13654bafe3e5130b146aeb7 btrfs: remove unnecessary memory barrier in btrfs_direct_IO Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx> ... simply removes the barrier. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
