On Mon, 23 Jun 2008 21:46:27 +1000 Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote: > On Monday 23 June 2008 21:25, Hidehiro Kawai wrote: > > A transient I/O error can corrupt inode data. Here is the scenario: > > > > (1) update inode_A at the block_B > > (2) pdflush writes out new inode_A to the filesystem, but it results > > in write I/O error, at this point, BH_Uptodate flag of the buffer > > for block_B is cleared and BH_Write_EIO is set > > (3) create new inode_C which located at block_B, and > > __ext3_get_inode_loc() tries to read on-disk block_B because the > > buffer is not uptodate > > (4) if it can read on-disk block_B successfully, inode_A is > > overwritten by old data > > > > This patch makes __ext3_get_inode_loc() not read the inode block if > > the buffer has BH_Write_EIO flag. In this case, the buffer should > > have the latest information, so setting the uptodate flag to the > > buffer (this avoids WARN_ON_ONCE() in mark_buffer_dirty().) > > > > According to this change, we would need to test BH_Write_EIO flag for > > the error checking. Currently nobody checks write I/O errors on > > metadata buffers, but it will be done in other patches I'm working on. > > IMO there is a problem with all the buffer head and pagecache error > handling in that uptodate gets cleared on write errors. This is not > only wrong (because the in-memory copy continues to contain the most > uptodate copy), but it will trigger assertions all over the mm and > buffer code AFAIKS. > > I don't know why it was done like this, or if anybody actually tested > any of it, but AFAIKS the best way to fix this is to simply not > clear any uptodate bits upon write errors. There's a plausible-sounding reason for this behaviour which I forgot about three years ago. Maybe Linus remembers? Meanwhile I guess I'll queue the patch, sad though it is. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
