On Wed, 23 Nov 2011 17:05:33 +0800 Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > On Wed, Nov 23, 2011 at 06:28:05AM +0800, Andrew Morton wrote: > > On Wed, 16 Nov 2011 19:44:21 +0800 > > Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > > > > > Due to the (very low) possibility of data loss by partial writes, IMHO > > > it would safer to test this patch in linux-next until next merge window, > > > > Any such bugs will not be discovered in linux-next testing. > > Yup, I'm afraid. > > > The only way to find these things in a reasonable period of time is to > > go in and find them. For example, intensive fsx-linux testing with > > concurrent heavy memory pressure on various filesystems with various > > block sizes. And of course concurrent signalling. If you're talking > > about O_DIRECT then iirc I hacked support for that into fsx-linux. I > > think. > > How are we going to measure the success/failure? Check if it > eventually resulted in filesystem corruption or whatever? yup. > When received SIGKILL, fsx-linux itself will just die. Well, there are ways of simulating its effect. For example, bale out of the write() every seventh time if current->comm=="fsx-linux". Or set a rearming timer which triggers a baled-out write. You'll work it out ;) > > Anyway, what _are_ the scenarios in which we think data can be lost? > > It's the vision that there may be partial writes on SIGKILL. Before > patch, the write will either succeed as a whole or not started at > all, depending on the timing of write/SIGKILL. This is kind of atomic > operation. However now the write can be half done. > > If the application really cares about atomic behavior, it can do > create-and-rename. However there are always the possibility of broken > applications. > > Maybe this is not that big problem as SIGKILL is considered be to > destructive already. Yeah, I have dim dark memories that there are subtle problems with interrupting write(). Linus might remember. Others might remember too, but we're only talking to fsdevel which nobody reads :( -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
