On Fri, 15 Aug 2008 18:09:58 -0400 Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Fri, Aug 15, 2008 at 02:08:50PM +1000, Lachlan McIlroy wrote: > > With the help from some tracing I found that we try to map extents beyond > > eof when doing a direct I/O read. It appears that the way to inform the > > generic direct I/O path (ie do_direct_IO()) that we have breached eof is > > to return an unmapped buffer from xfs_get_blocks_direct(). This will cause > > do_direct_IO() to jump to the hole handling code where is will check for > > eof and then abort. > > > > This problem was found because a direct I/O read was trying to map beyond > > eof and was encountering delayed allocations. The delayed allocations beyond > > eof are speculative allocations and they didn't get converted when the direct > > I/O flushed the file because there was only enough space in the current AG > > to convert and write out the dirty pages within eof. Note that > > xfs_iomap_write_allocate() wont necessarily convert all the delayed allocation > > passed to it - it will return after allocating the first extent - so if the > > delayed allocation extends beyond eof then it will stay that way. > > > > This change will detect a direct I/O read beyond eof: > > The change looks good to me, but I really think the direct I/O could > should never send down requests like this down to the filesystems. akpm > and -fsdevel Cc'ed. Oh gee, I forget, and so many people have done drivebys on that code... We _could_ add additional i_size checking into direct-io.c but bear in mind that it would be best-effort unreliable stuff. The code will still be tripped up by concurrent extends and concurrent truncates. So we'll still end up calling the fs for blocks outside i_size, only less commonly. I think. -- 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
