On Fri, Jan 29, 2016 at 04:34:30PM -0700, Ross Zwisler wrote: > On Fri, Jan 29, 2016 at 11:28:15AM -0700, Ross Zwisler wrote: > > On Thu, Jan 28, 2016 at 01:38:58PM -0800, Christoph Hellwig wrote: > > > On Thu, Jan 28, 2016 at 12:35:04PM -0700, Ross Zwisler wrote: > > > > There are a number of places in dax.c that look up the struct block_device > > > > associated with an inode. Previously this was done by just using > > > > inode->i_sb->s_bdev. This is correct for inodes that exist within the > > > > filesystems supported by DAX (ext2, ext4 & XFS), but when running DAX > > > > against raw block devices this value is NULL. This causes NULL pointer > > > > dereferences when these block_device pointers are used. > > > > > > It's also wrong for an XFS file system with a RT device.. > > > > > > > +#define DAX_BDEV(inode) (S_ISBLK(inode->i_mode) ? I_BDEV(inode) \ > > > > + : inode->i_sb->s_bdev) > > > > > > .. but this isn't going to fix it. You must use a bdev returned by > > > get_blocks or a similar file system method. > > > > I guess I need to go off and understand if we can have DAX mappings on such a > > device. If we can, we may have a problem - we can get the block_device from > > get_block() in I/O path and the various fault paths, but we don't have access > > to get_block() when flushing via dax_writeback_mapping_range(). We avoid > > needing it the normal case by storing the sector results from get_block() in > > the radix tree. > > > > /me is off to play with RT devices... > > Well, RT devices are completely broken as far as I can see. I've reported the > breakage to the XFS list. Anything I do that triggers a RT block allocation > in XFS causes a lockdep splat + a kernel BUG - I've tried regular pwrite(), Set CONFIG_XFS_DEBUG=n (assert failure that can be ignored causing the bug, and lockdep simply has an annotation problem) and it should work. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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
